The Design and Build of Biodigester Toilet

SCHOOL OF MECHANICAL ENGINEERING

Project 1587:

The Design and Build of a Biodigester Toilet

James Bass

Nishanth Cheruvu

Natasha Rayan

Charlie Savory

Kieren Sheehan

Supervisors: Dr Cristian Birzer and Dr Paul Medwell

24 October 2014

Word count: 29,797

Executive Summary

Preventable diseases caused by unsafe sanitation practices, and respiratory issues created by burning

solid fuels for cooking, heating, and lighting kill millions of people in developing communities every

year. Providing improved sanitation facilities, and replacing solid fuels (such as wood and dung) with

clean burning modern fuels can improve quality of life for billions of people around the globe, and save

millions of lives each year. A biodigester toilet is a single solution to both of these major issues; it

provides an integrated waste management facility that will convert human excreta into clean burning

biogas, which can be used for cooking, heating, and lighting.

Research was conducted to obtain the background knowledge required to design a biodigester system

that would be capable of successfully producing biogas, while also providing an alternative to unsafe

sanitation practices. A dual tank digester design was chosen, to provide a clarification tank as a

precursor to effluent post-treatment. A thorough risk assessment was performed before construction

and testing of a prototype was conducted. Sponsorship from Barrow and Bench Mitre 10 Malvern,

Caroma and Lynair Logistics enabled the project team to source parts within the project budget, and

construct the prototype. Testing was undertaken at Urrbrae Agricultural High School to determine

whether the system was capable of effectively isolating waste and producing biogas.

The prototype effectively separated feedstock from human contact, and harnessed the anaerobic di-

gestion process to produce biogas. As methane is the primary constituent of biogas, its concentration

was measured throughout the testing period. Results showed an increase in methane concentration,

however the testing period was concluded before flammable biogas was produced. All data indicated

that the anaerobic digestion process was progressing as expected, and it is likely that flammable biogas

would have been produced, given a longer testing period.

i

Acknowledgements

The team would like to thank the following individuals and organisations for their contributions.

Project Supervisors

Dr. Cristian Birzer and Dr. Paul Medwell

Sponsors

Barrow and Bench Mitre 10 Malvern

The University of Adelaide School of Mechanical Engineering

Lynair Logistics

Caroma

Special Thanks

The staff of Urrbrae Agricultural High School

The staff of Barrow and Bench Mitre 10 Malvern

Rob Patterson

Michael Hatch

ii

Statement

This work contains no material which has been accepted for the award of any other degree or diploma

in any university or other tertiary institution and, to the best of our knowledge and belief, contains

no material previously published or written by another person, except where due reference has been

made in the text.

The project team consents to this copy of their report, when deposited in the University Library, being

available for loan and photocopying.

iii

Contents

Executive Summary i

Acknowledgements ii

Signed Statement iii

Nomenclature x

1 Introduction 1

1.1 Report Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Background 3

2.1 Sanitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Solid Fuels and Household Air Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 The Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.4 Project Aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 Technical Background 13

3.1 Human Waste Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Single Appropriate Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.3 Anaerobic Digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4 Biodigester Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.5 Existing Biodigester Toilets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4 Scope, Objectives and Timeline 31

4.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.2 Core Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.3 Extension Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.4 Project Timeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5 Design Formation 34

iv

5.1 Standards and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5.2 Overall Design Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.3 Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.4 Essential Design Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.5 Conceptual Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

6 Final Design 54

6.1 Final System Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6.2 Number of End Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6.3 Materials Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

6.4 Waste Collection System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

6.5 Gas Collection System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

7 Risk Assessment 71

7.1 Likelihood Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

7.2 Consequence Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

7.3 Risk Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

7.4 Heirarchies of Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

7.5 Risk Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

8 Prototype Construction and Cost 76

8.1 Part Sourcing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

8.2 Construction and Tooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

8.3 Personal Protective Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

8.4 Costing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

9 Testing and Operation Procedures 82

9.1 System Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

9.2 Prototype Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

9.3 Feedstock Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

9.4 System Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

9.5 Continuous Process Digester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

9.6 Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

9.7 Biogas Collection and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

9.8 Safe Operating Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

10 Results and Discussion 89

10.1 Gas Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

10.2 Methane Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

10.3 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

10.4 Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

10.5 Portability Demonstration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

10.6 Completion of Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

11 Future Work 98

11.1 Extension Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

11.2 Design Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12 Conclusion 100

Appendix A Project Timeline 109

Appendix B CAD Drawings 114

Appendix C Australian Standards for Polyethylene Pipes 126

Appendix D Australian Standard Gas System Design Factors 130

Appendix E Stirrer CAD Drawings 132

Appendix F Risk Assessment 148

Appendix G Project Cost Matrix 153

Appendix H Sponsorship Prospectus 155

Appendix I Project Hours Spent by Individual Team Members 158

Appendix J SupelTM Sampling Bag Data Sheet 165

Appendix K Picarro Gas Analyser Data Sheet 168

Appendix L Testing Numerical Results 171

List of Figures

2.1 The proportion of the population using improved sanitation (WHO and UNICEF, 2012) 4

2.2 Pit latrine with squatting slab (Furniss, 2011) . . . . . . . . . . . . . . . . . . . . . . 6

2.3 A Chinese shared pit latrine without a platform, slab or seat (Rivard, 2005) . . . . . . 6

2.4 Hanging toilet in Port Haitien, Haiti (Stauffer, 2014) . . . . . . . . . . . . . . . . . . . 7

2.5 Indication of household solid fuel use globally (Chartsbin (2007) using data from WHO

(2007)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 Effect of solids retention time and temperature on volatile solids reduction in a labora-

tory scale anaerobic digester (Wang et al., 2007) . . . . . . . . . . . . . . . . . . . . . 19

3.2 Fixed dome biodigester (Weir, n.d.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.3 Floating drum biodigester (Thai Biogas Energy Company, 2008) . . . . . . . . . . . . 23

3.4 Plastic tube plug flow biodigester. Adapted from Energypedia (2014) . . . . . . . . . . 23

3.5 Dismountable FRP biodigester model (Cheng et al., 2014) . . . . . . . . . . . . . . . . 25

3.6 Biodigester created from existing water tanks in Cambodia (Engineers Without Borders,

2011) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.7 ARTI bioidigester: A prefabricated plastic product based on the existing floating drum

design (Zu, 2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.8 EWB Challenge biodigesting toilet (Ashley et al., 2011) . . . . . . . . . . . . . . . . . 27

3.9 Prototype design with flexible membrane gas collection (Coffee et al., 2009) . . . . . . 29

3.10 Prototype design with gasometer gas collection (Coffee et al., 2009) . . . . . . . . . . . 29

5.1 Concept Design 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.2 Concept Design 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.3 Concept Design 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

5.4 Concept Design 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.5 Final concept design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6.1 Drawing of inlet assembly (dimensions in mm) . . . . . . . . . . . . . . . . . . . . . . 58

6.2 Final attached lid for second tank in the system . . . . . . . . . . . . . . . . . . . . . . 59

vii

6.3 First tank attached gas connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6.4 Gas connection valve on second tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6.5 A typical bioball shape (Foster and Smith, 2014) . . . . . . . . . . . . . . . . . . . . . 61

6.6 Attached tank flange with neoprene seal . . . . . . . . . . . . . . . . . . . . . . . . . . 62

6.7 Attached ball valve and barb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

6.8 Attached ball valve, barb, and suction hose . . . . . . . . . . . . . . . . . . . . . . . . 63

6.9 Overall connection between two tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

6.10 Outlet tap attached to existing 25 mm diameter threaded hole . . . . . . . . . . . . . 64

6.11 Connection between gas collection membrane and pipe network . . . . . . . . . . . . . 65

6.12 1m3 biogas collection membrane used in the final design . . . . . . . . . . . . . . . . . 67

6.13 Scrap material used for insulation layer . . . . . . . . . . . . . . . . . . . . . . . . . . 68

6.14 Black plastic layer for heat absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

6.15 Final Stirrer Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

9.1 Tedlar bag filled with gas sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

10.1 Change in methane concentration over testing period . . . . . . . . . . . . . . . . . . . 90

10.2 Change in methane concentration for different substrates (Sulistyo et al., 2012) . . . . 91

10.3 Change in system pH over testing period . . . . . . . . . . . . . . . . . . . . . . . . . . 92

10.4 Temperature measurements compared to BOM readings . . . . . . . . . . . . . . . . . 94

A.1 Project Gantt Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

A.2 Project Gantt Chart continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

A.3 Project Gantt Chart continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

B.1 Overall CAD model of prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

E.1 Overall CAD model of stirrer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

List of Tables

3.1 Chemical constituents of biogas (Favre et al., 2009) . . . . . . . . . . . . . . . . . . . . 17

3.2 Biogas production for different animal feedstocks (Junfeng et al., 2005) . . . . . . . . . 18

3.3 C/N ratio of some organic materials (Karki and Dixit, 1984) . . . . . . . . . . . . . . 20

5.1 Relevant Australian Standards (Davidson et al., 2013) . . . . . . . . . . . . . . . . . . 35

5.2 Relevant recommendations for biogas installations relating to a small scale biodigester

toilet (Davidson et al., 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.3 Concept Design 1 design criteria analysis . . . . . . . . . . . . . . . . . . . . . . . . . 42




5.7 Evaluation matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5.8 Design feature summary table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

5.9 Final concept design design criteria analysis . . . . . . . . . . . . . . . . . . . . . . . . 53

6.1 Properties of PE100 pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

7.1 Consequence scale - risks to project success (The University of Adelaide, 2012) . . . . 72

7.2 Consequence scale - safety risks (The University of Adelaide, 2012) . . . . . . . . . . . 73

7.3 Risk matrix (The University of Adelaide, 2012) . . . . . . . . . . . . . . . . . . . . . . 73

7.4 Risk management required (The University of Adelaide, 2012) . . . . . . . . . . . . . . 74

8.1 Sponsorship summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

8.2 Prototype cost summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

8.3 Recycled component alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

A.1 Project Review Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

A.2 Major Milestones, Review Gates and Due Dates . . . . . . . . . . . . . . . . . . . . . . 110

ix

Nomenclature

AUD Australian Dollar(s)

BOM Bureau of Meteorology

textitC Design factor

CoP Code of Practice

C/N Carbon to nitrogen ratio

CAD Computer Aided Design

Dm min Minimum mean outside diameter

FRP Fiber Reinforced Plastic

GACC Global Alliance for Clean Cookstoves

L Litre

LPG Liquefied Petroleum Gas

m Metre

MAOP Maximum Allowable Operating Pressure

MDGs Millennium Development Goals

mm Millimetre

MRS Maximum Required Strength

NGO Non-governmental Organisation

PPE Personal Protective Equipment

ppm Parts per million

PE Polyethylene

PVC Polyvinyl Chloride

x

RT Retention time

SDR Standard Dimension Ratio

SOP Safe Operating Procedure

Tmin Minimum wall thickness

UAHS Urrbrae Agricultural High School

UNICEF The United Nations Children’s Fund

USD United States Dollar(s)

UV Ultra-Violet

VS Volatile Solids

WHO World Health Organisation

Chapter 1

Introduction

Currently, 2.6 billion people worldwide lack access to adequate sanitation facilities, while 3 billion

people are put at risk from harmful air pollution because they rely on burning solid fuels for cooking,

heating and lighting. Over 4.6 million deaths are caused every year from a wide range of health issues

related to poor sanitation and household air pollution (WHO, 2014; WHO and UNICEF, 2014c). When

considering the global distribution of these problems, it is clear that they are present in similar regions

all over the world; primarily the rural areas of developing countries. Some of the most marginalised

people in the world are subject to diseases associated with exposure to human faeces, along with

serious respiratory health issues (including lung cancer) caused by household air pollution. While not

tolerated in more developed nations, crippling poverty means billions of people living in developing

countries are subject to these conditions every day. Developing a single, cheap solution that will

provide improved means of sanitation while reducing reliance on solid fuels has the potential to save

the lives of millions, and improve the lives of billions, every year.

The design and build of a biodigester toilet is a humanitarian project aimed at providing improved

sanitation facilities, and reducing air pollution for the billions of people affected by these issues.

For this project, a toilet is integrated with a biodigester - a device that stores and ‘digests’ organic

material while also producing biogas, a mixture of primarily methane (CH4) and carbon dioxide (CO2).

Designing a biodigester to accommodate a toilet enables it to become an integrated waste management

system, and provides a means of safe human waste disposal. The biogas produced from the digestion

of human waste can be used as a cleaner burning alternative to solid fuels for cooking, heating, and

lighting. Thus, both issues of unsafe sanitation and household air pollution may be addressed through

implementation of a functional biodigester toilet.

While the concept and use of the biodigester is widespread and well documented, there remain inade-

quacies in the literature pertaining to a system designed solely for use with human waste. Combined

biodigester and toilet systems have been designed and tested in the past, however experimental results

1

CHAPTER 1. INTRODUCTION 2

from these existing systems indicate that neither design, nor execution, were suitable for the system

to have practical applications. Several explanations as to why the systems were ineffective have been

suggested in the literature, but not subsequently implemented into an improved design. An improved

design will better address the health, sanitation, and energy challenges prevalent in many develop-

ing regions. Furthermore, as biodigester systems produce useful secondary products from primary

waste, there is scope for application in developed countries. Research and development into improved

biodigester toilet designs for developed countries could alleviate concerns of growing waste volume,

energy shortages, and climate change. The integration of biodigester toilets into modern waste man-

agement and energy consumption practices could promote greater self-sufficiency, and environmental

sustainability.

1.1 Report Structure

A detailed outline of the global distribution of poor sanitation practices and the use of solid fuels

for cooking, heating, and lighting is presented within the Background chapter of this report. Also

included in this chapter is an outline of the major health problems related to these practices. The

problems outlined in this chapter helped guide the development of the project aim.

After the project aim is identified, the Technical Background chapter presents research into existing

technologies that provide a means of achieving the overall project aim. Of particular focus is methods

of human waste management as well as waste collection systems.

The Scope, Objectives, and Timeline chapter outlines detailed objectives for the project, specifically

relating to the design, build and subsequent testing of a biodigester toilet. A timeline of the project

is also presented in this chapter.

The information presented in the initial chapters is then used in the Design Formation chapter to

develop several concept designs of biodigester toilets. These designs are evaluated against a list of

design criteria. Based on the analysis of the concept designs, a final design is further developed in the

Final Design chapter.

The Risk Assessment, Prototype Construction and Cost, and Testing and Operation chapters outline

the various stages in the production of a prototype biodigester toilet, based on the final design. A risk

assessment was required to ensure construction and testing could be performed safely.

Preliminary testing results, and a discussion of their significance, are presented in the Results and

Discussion chapter. The extent to which the prototype was able to achieve all core project objectives is

assessed in this chapter. Based on these preliminary testing results and the overall effectiveness of the

prototype, possible design modifications and additions are discussed in the Future Work chapter.

Chapter 2

Background

Household air pollution produced by burning solid fuels, and inadequate sanitation are two major

issues facing the developing world. Both problems cause specific health, social, and environmental

issues. Significant improvements have been made in both these areas over the last fourteen years since

the conception of the millennium development goals in 2000 (WHO, 2012) with scope for substantial

progress in the future. Presented in this chapter is a discussion of these problems, along with informa-

tion about biodigesters, biogas, and the contribution they make to alleviating inadequate sanitation,

and household air pollution.

2.1 Sanitation

Currently 2.6 billion people worldwide do not have access to adequate sanitation facilities, resulting

in the contraction of diseases that are responsible for more than two million deaths every year (WHO

and UNICEF, 2014c). Additionally, there are a number of non-fatal diseases associated with poor

sanitation that significantly reduce quality of life. These issues associated with inadequate sanitation

are primarily present in developing communities. Therefore, the development of sanitation systems

that are readily available in affected regions will help improve the quality of life of billions of people

and save a significant number of lives every year.

2.1.1 Location of Current Practices

The distribution of global access to improved sanitation facilities is shown in Figure 2.1. The definition

of an improved sanitation facility is presented in Section 2.1.3. It can be seen that Africa and the

Indian Subcontinent are the worst affected, where most of the countries have less than 50% access.

China, South-East Asia, and Latin America are also affected, though not to the same extent.

3

CHAPTER 2. BACKGROUND 4

Figure 2.1: The proportion of the population using improved sanitation (WHO and UNICEF, 2012)

The global divide of access to improved sanitation is also disproportionately split between the rural

and urban regions. Currently 79% of people living in urban areas have access to improved sanitation

facilities. Conversely, only 47% of people living in rural areas enjoy the same access. Therefore 1.8

billion people worldwide are unable to use improved sanitation facilities, primarily due to the cost of

sanitation facilities in these areas (WHO and UNICEF, 2012). Open defecation occurs primarily in

rural areas; worldwide, 950 million rural residents are forced to practice open defecation compared to

100 million people living in urban locations (WHO and UNICEF, 2012). Open defecation is mainly

concentrated in India, whose population makes up over 60% of the total world population practicing

this type of unimproved sanitation (WHO and UNICEF, 2012).

2.1.2 Health Issues

There are a number of diseases and associated conditions that can arise from the practice of unimproved

sanitation and subsequent contact with human excreta. These include diarrhoea, cholera, fluorosis,

guinea worm disease, hepatitis A, schistosomiasis, trachoma, and typhoid (UNICEF, 2014). Diarrhoea,

schistosomiasis, trachoma, and typhoid are commonly considered the most damaging and widespread

conditions (UNICEF, 2014).


Diarrhoea

A condition causing the loss of water and electrolytes in a person, leading to dehydration and

sometimes death. With four billion cases occurring annually and 1.8 million deaths (1.6 million

being children under five years old), it is the main health problem associated with poor sanitation

practices (UNICEF, 2014).

Schistomsomiasis

A disease caused by parasitic worms that penetrate the skin of people who come into contact with

contaminated water. It affects 200 million people every year, with 20 million suffering serious

consequences and approximately 200,000 dying annually (Fenwick, 2012; UNICEF, 2014). It is

estimated that adequate sanitation could reduce infection rates by 77% (UNICEF, 2014).

Typhoid

A bacterial infection that can result in headaches and nausea. It affects 12 million people

annually, and is contracted by consuming contaminated food or water (UNICEF, 2014).

Trachoma

An infectious bacterial disease which causes a roughening of the inner surface of the eyelid leading

to pain and possible blindness. Approximately six million people are currently blind because of

this disease. It is estimated that adequate sanitation could reduce infection rates by up to 25%

(UNICEF, 2014).

2.1.3 Definitions and Practices

The WHO classifies sanitation facilities in two broad terms; improved sanitation and unimproved

sanitation facilities. Improved sanitation facilities “...hygienically separate human excreta from human

contact.” (WHO and UNICEF, 2014a). Common toilets that meet this criteria include the western

style flush toilet, flush and pour systems into a pit-latrine (shown in Figure 2.2), and septic tanks.


Figure 2.2: Pit latrine with squatting slab (Furniss, 2011)

Unimproved sanitation facilities and practices typically do not separate human excreta from human

contact. Latrines without a squatting slab, platform or seat, and hanging toilets that dispose of waste

directly into a river or similar body of water are typical examples of unimproved facilities. They are

pictured in Figures 2.3 and 2.4, respectivley. Shared sanitation facilities are also classified as unim-

proved sanitation. Shared sanitation facilites are “...sanitation facilities of an otherwise acceptable

type that are shared between two or more households.” (WHO and UNICEF, 2014b)

Figure 2.3: A Chinese shared pit latrine without a platform, slab or seat (Rivard, 2005)


Figure 2.4: Hanging toilet in Port Haitien, Haiti (Stauffer, 2014)

2.2 Solid Fuels and Household Air Pollution

Burning solid fuels, or ‘biomass’, for cooking, heating, and lighting creates significant household air

pollution, and is a serious global issue. Approximately three billion people worldwide rely on burning

solid fuels such as wood, charcoal, dung, and crop residues for their cooking, heating, and lighting

requirements (WHO, 2014). The majority of these people live in developing countries in Africa and

Asia (Rehfuess et al., 2011) where access to improved fuels is restricted by economic, and social

factors. Burning solid fuels releases harmful emissions such as carbon monoxide (CO), carbon dioxide

(CO2), oxides of nitrogen (NOX), and particulate matter into the surrounding atmosphere. When this

is performed indoors it can cause significant household air pollution, especially in poorly ventilated

buildings; this causes serious health effects that result in the deaths of 4.3 million people annually

(WHO, 2014). There are also negative environmental and social effects associated with biomass

burning. These include contributions to global greenhouse gas emissions, and gender inequalities.

The eight United Nations Millennium Development Goals (discussed further in Section 2.3.1) are

goals that when achieved, will significantly improve the lives of the worlds most vulnerable people.

Reducing household air pollution produced from solid fuels will make a direct contribution to achieving

MDGs 1,3,4,5 and 7 (WHO, 2014).

2.2.1 Locations of Solid Fuel Usage

The global distribution of solid fuel use is shown in Figure 2.5. It can be seen that the problem is

concentrated in developing countries in Africa and Asia. Over 86% of the population in most African

countries, and especially those in the Sub-Saharan Africa region, use solid fuels (GACC, 2014). In

most parts of Asia the average rate is lower at approximately 52-66% (GACC, 2014), but still highly


significant. The death rate in each country logically follows the proportion of solid fuel use of the

population. In Sub-Saharan Africa, between 400-600 people per million die due to solid fuel usage

while in Asia, this is between 200-300 people per million (Ezzati et al., 2005).

Figure 2.5: Indication of household solid fuel use globally (Chartsbin (2007) using data from WHO

(2007))

2.2.2 Health Implications

There are a large number of health issues that arise from smoke inhalation and household air pollu-

tion. Some of the most common issues are pneumonia, chronic obstructive pulmonary disease, and

lung cancer, which represent 12%, 22% and 6% of the total 4.3 million annual deaths associated with

household air pollution, respectively (WHO, 2014). Acute lower respiratory infections including pneu-

monia are especially vicious, having the greatest effect on young children. Over half of the pneumonia

related deaths worldwide in children under five years of age are caused by household air pollution

produced during the combustion of solid fuels (WHO, 2014).

Other issues that seriously affect quality of life, but are not necessarily fatal, include cataract contrac-

tion (which can result in blindness), asthma, and burns (WHO, 2014). While it is difficult to compare

these issues to the fatal conditions, the negative effect they have on the ability of people to function in

life, and of developing countries to improve their situation, cannot be underestimated. Overall, it can

be seen that the problems resulting from solid fuel use, which causes harmful household air pollution,

are some of the most serious global health issues today.


2.2.3 Environmental Implications

As well as the health related problems discussed in Section 2.2.2, there are a number of significant

environmental issues brought about by the burning of solid fuels. These include contributions to the

greenhouse effect, and deforestation.

The inefficient performance of most cook stoves in the developing world contributes to the greenhouse

effect. In these devices, most fuels undergo a significant degree of incomplete combustion resulting

in the emission of black carbon (soot) into the atmosphere. Soot is one of the largest contributors

to climate change, following CO2 and methane (CH4) (Bond and Sun, 2005). It is estimated that

household solid fuel burning accounts for 18% of these emissions globally (Bond and Sun, 2005).

2.2.4 Social Implications

Women and children are often given the task of gathering fuel for cooking, lighting, and heating

(Parikh, 2011; WHO, 2014). This activity can take a significant period of time, and limits the time

available for schooling, income generation, and other opportunities for economic development (WHO,

2014). The fact that these tasks are often limited to daylight hours only exacerbates the problem.

According to the World Health Organization (2014), women and children also face serious risk of

injury and violence while gathering fuel.

As women are often responsible for household cooking, they are more exposed to air pollution created

in cooking and heating practices (WHO, 2014). Along with women being disproportionately affected

by the use of solid fuels, more than 50% of worldwide deaths among children under five years old can

be directly attributed to household air pollution created by solid fuel use (WHO, 2014).

2.2.5 Modern Fuels and Clean Cookstoves

The main alternatives to biomass burning are modern fuels and clean cookstoves. The term ‘modern

fuels’ encompasses liquefied petroleum gas (LPG), kerosene, ethanol, biodiesel, and biogas. Modern

fuels are superior to solid fuels as they produce fewer harmful emissions (Rehfuess et al., 2011). This

largely eliminates most of the health, environmental, and social issues associated with solid fuel use.

Clean cookstoves are an intermediate measure that still burn biomass, but achieve similar advantages

as using modern fuels.

The main obstacles to modern fuel uptake are affordability, and availability (Foell et al., 2011). For

this reason uptake is significantly higher in wealthier urban areas, where the availability of fuels is

higher due to the centralised location. In rural areas the clean cookstove is often a more attractive

alternative than modern fuels, due to the lower costs and widespread biomass availability (Foell et al.,


2011). Modern fuel uptake is also affected by cultural preferences. In many cases, even when modern

fuels are readily available and affordable, existing practices will be maintained exclusively, or a mix of

the two options applied (Masera et al., 2000). The motivations behind this are varied, including the

preference for smoke as a mosquito repellent, and cultural practices such as using flat pans for cooking

traditional tortillas in Mexico (Masera et al., 2000). Biogas is one modern fuel that has a history of

widespread uptake in developing countries.

By 2007, 26.5 and four million domestic biogas generators (or ‘biodigesters’) were present in China

and India, respectively (Surendra et al., 2013). The Netherlands Development Organisation (SNV),

has also installed over 500,000 domestic biodigesters across Asia and Africa (Surendra et al., 2013).

Biodigester programs have been set up by governments in many developing countries to promote biogas

production (Buysmanc and Mol, 2013). In these cases, a local biodigester market was created through

initial financial and technical training. High construction costs have prevented these markets from

becoming entirely self-sustainable, and currently most people are still partly reliant on government

assistance to purchase a biodigester (Buysmanc and Mol, 2013). While this reliance on government

assistance is obviously a weakness in the programs, they have been highly successful in terms of the

quality and scale of biodigester dissemination (Buysmanc and Mol, 2013). Clearly, biogas is a modern

fuel that has a history of uptake in developing countries, and as such is considered an excellent potential

replacement for solid fuels.

2.3 The Connection

Based on the information presented in Figures 2.1 and 2.5, it is clear that the countries with the

highest population proportions using unimproved sanitation facilities also have high incidences of

solid fuel use. These countries are some of the most poverty stricken in the world (Socioeconomic

Data and Applications Center, 2005). Therefore, people living in these areas are likely subjected to a

combination of the serious health issues presented by poor sanitation practices, respiratory problems

created by household air pollution, and minimal means to improve their situation due to the poverty

distribution within their country.

As the problems outlined in Sections 2.1 and 2.2 are primarily concentrated in the same poverty

stricken areas, it makes sense to develop a single, cheap solution to both major issues. This way, a

single method can be used to minimise the impact of problems arising from both unsafe sanitation

practices, and solid fuel use. Defining one solution would also prove easier to implement and integrate

into the regions where it is most required. Having a single solution to both these issues will also make

significant inroads into progress towards the Millennium Development Goals.


2.3.1 Sanitation, Solid Fuels and the Millennium Development Goals

The eight United Nations Millennium Development Goals (MDGs) were created in 2000 to quanti-

tatively measure and target the progress of developing nations. Almost all of these goals relate in

some way to improving sanitation and modern fuel usage in the developing world. All the Millenium

Development Goals, with the exception of Goal 2 and Goal 8, are especially relevant.

The United Nations Millennium Development Goals (United Nations, 2014)

1. To eradicate extreme poverty and hunger

The use of modern fuels eliminates the need to collect traditional solid fuels which can often be

a highly time consuming process. Saving time allows the pursuit of income generating activities,

and education.

2. To achieve universal primary education

3. To promote gender equality and empower women

Solid fuel usage was shown to disproportionately affect women; reducing the use of solid fuels

will significantly act to address this inequality.

4. To reduce child mortality

Household air pollution from solid fuel usage disproportionately affects children to a significant

degree, as shown in Section 2.2.2. Modern fuels produce less household air pollution, and

therefore help to address this goal. In addition, improving sanitation practices will reduce the

incidences of children contracting diseases from unsuitable sanitation facilities.

5. To improve maternal health

The use of modern fuels will reduce the exposure of women to household air pollution. According

to WHO (2014), reducing household air pollution will help to achieve this MDG.

6. To combat HIV/AIDS, malaria and other diseases

Providing improved sanitation facilities will significantly reduce the devastating diseases associ-

ated with poor sanitation, while use of clean burning modern fuels will help reduce incidences

of health problems related to household air pollution.


7. To ensure environmental sustainability

There are a number of environmental issues associated with the use of solid fuels, explored

in Section 2.2.3. Reducing household air pollution will negate many of these environmental

problems. Providing improved sanitation facilities will also reduce incidences of open defecation,

making for cleaner water bodies.

8. To develop a global partnership for development

2.4 Project Aim

Based on the information presented in this chapter, it is clear that poor sanitation and solid fuel use

are two independent problems causing serious negative effects for billions of people worldwide. Both

problems are typically concentrated in the same developing countries, and often affect the same people.

It is clear that developing a single solution to both of these problems will have a positive impact on

billions of lives worldwide, and has the potential to prevent up to 4.3 million deaths each year. This

leads to the overall aim of the project:

To develop a single appropriate technology that may be implemented in developing communities in

order to alleviate the dangers associated with unsafe sanitation practices and the household burning

of solid fuels.

Chapter 3

Technical Background

3.1 Human Waste Management

It is necessary to consider various waste management techniques in order to develop an appropriate

technology that will help alleviate the dangers associated with unsafe sanitation practices. The term

‘waste management’ comprises practices relating to the treatment and subsequent recycling or disposal

of human waste.

3.1.1 Harmful Pathogens and Health Implications

A pathogen is a broad term for any infectious virus, bacteria, parasite or fungi that may cause disease

to the host organism. They are present in human and animal excreta, contaminated food, industrial

facilities, along with other sources (Wang et al., 2007). Pathogens from human excreta enter the

human body through a number of pathways including direct transmission from inadequate sanitation

facilities, contaminated water sources and contaminated crop fields (WHO and UNICEF, 2012).

Feachem et al. (1980) explains how there is a large range of bacterial pathogens that can grow and

reproduce in excreta under different environmental conditions. Common bacteria include salmonellae,

shigella, vibrios, pathogenic E. coli, Yersinia and campylobacter (Feachem et al., 1980). Bacteria can

remain active for long periods. They become dormant in low temperatures but are likely to become

inactivated under high temperatures. Diarrhoea or gastroenteritis are common symptom of bacterial

infection.

Destruction of these pathogens is a key priority for waste management systems. Human exposure to

harmful pathogens at any stage during the waste management process could result in severe health

implications. Most pathogens in excreta can be minimised by employing one or more various treatment

methods.

13

CHAPTER 3. TECHNICAL BACKGROUND 14

3.1.2 Wastewater Treatment Methods

Wastewater management is a collection of processes that remove the contaminants from wastewater

and sewage. The objective of wastewater management is to convert potentially harmful sewage waste

into a safe product which can be returned to the environment.

3.1.2.1 Sedimentation

As described by Wang et al. (2007), sedimentation is a process involving the separation of dense

suspended particles in a mixture from a lower density fluid, and is often the first phase in a water

treatment process. In sedimentation tanks, solids accumulate at the bottom of the tank to form a

sludge. This process is usually followed by a secondary decantation procedure to separate the sludge

from the fluid.

3.1.2.2 Aerobic Treatment

Aerobic treatment is a process during which biodegradable matter is broken down in the presence of

oxygen, and is commonly referred to as aerobic digestion. Organic matter is oxidised and decomposed

by micro-organisms which feed on the organic material. The basic procedure consists of aerating the

waste in order to oxidise the solids, then allowing the sludge to begin sedimentation. Once settled,

water is decanted, and digested solids are removed or pumped back into the system. During the

oxidation process, organic mass is broken down into carbon dioxide (CO2) and water (H2O), nitrates,

sulphates and energy in the form of heat (Wang et al., 2007).

Odours are minimised during storage and sludge quantities are reduced by removing volatile solids

during aerobic digestion. Aerobic treatment processes are used by many wastewater treatment facilities

due to shorter retention times. One drawback of aerobic digestion is the external energy requirement.

Energy is required to pump recycled bacteria from the settled solids back into the system, along with

providing a continuous oxygen supply to the system (Wang et al., 2007).

3.1.2.3 Anaerobic Treatment

Anaerobic treatment utilises the anaerobic digestion process which breaks down biodegradable matter

in the absence of oxygen (Lettinga, 1995). The process is known to occur naturally in some soils

and lakes where oxygen is restricted, and can also be induced by enclosing organic matter within

a gas-tight vessel to eliminate the supply of oxygen. This gas-tight vessel is commonly referred to

as a ‘biodigester’. Under suitable conditions, the organic material is digested by naturally occurring

anaerobic bacteria which significantly reduces pathogen content of the material (Mata-Alvarez et al.,


2000). In addition to reducing pathogen content, anaerobic digestion produces a flammable gas by-

product, commonly known as biogas (Caruana and Olsen, 2012). The production of biogas offers

a unique advantage of anaerobic treatment over other treatment methods; biogas can be used for

cooking, heating and lighting, as well as electricity generation.

The main drawback of anaerobic digestion is the temperamental nature of the anaerobic bacteria.

They are highly sensitive to fluctuating environmental conditions, and if they are not retained within

the system, organic compounds will not be effectively broken down. This will result in ineffective

pathogen treatment and a low biogas yield (Smith et al., 2005).

3.1.2.4 Decomposition

Decomposition, or composting of organic materials is another method of treating potentially harmful

waste products whilst producing a useful by-product. Bacteria and organisms decompose organic

matter into compost. In regards to human waste composting, the end product has minimal odour,

levels of pathogens which are safe for human handling, and may be applied to gardens and crops as a

nutritional soil conditioner and fertiliser (Wang et al., 2007).

Composting is advantageous in locations with a lack of landfill availability for waste disposal, as the

composted product takes up much less space than the primary organic material. As the end product

is a nutritional fertiliser, it can also be used in local agriculture operations. As the composting system

is low cost and effective, it may be appropriate to implement subsequent to anaerobic digestion so

that any exploitable energy by-products are extracted first (Jenkins, 2005).

3.1.3 Toilets

Fundamentally, a toilet is a sanitation facility designed to separate human waste from human contact

by transporting excreta to a location where it is less exposed. Traditionally, wastes were removed from

the human interface using dry systems which collected excreta in a large container or trench. These

systems are still commonly used in rural regions and in a majority of the developing world (Jenkins,

2005). Modern toilets in developed countries are wet systems which use a flush mechanism to remove

the wastes from human exposure, and transport it to a treatment facility.

The standard flushing toilet is not regarded as self-sustainable from a waste management perspective.

In most cases, flushing toilets simply transport waste from the human body to a sewer or septic tank,

the contents of which are eventually transported to a wastewater management facility for further

treatment. Once the water is treated, often with antibacterial chemicals, it is released back into the

environment. The solid matter is occasionally recycled into fertiliser but often discarded in landfills. In


some cases the flushing toilet is linked to a self-contained waste treatment unit or septic system which

allows for waste management on site (Jenkins, 2005). Self-contained waste management systems have

potential for environmental sustainability and also lower costs as the waste management processes can

be conducted at or near the toilet site and do not necessarily require as much infrastructure, water,

or treatment methods.

3.2 Single Appropriate Technology

As introduced in Section 2.4, the overall aim of the project is “To develop a single appropriate technol-

ogy that may be implemented in developing communities in order to alleviate the dangers associated

with unsafe sanitation practices and the household burning of solid fuels.”. Improving sanitation prac-

tices using a single technical solution requires the integration of a waste management method with a

toilet. This way, waste is separated from human contact at the source using the toilet, and is treated

by the integrated waste management system. Of the waste management systems considered in Sec-

tion 3.1, anaerobic digestion is the only method that will reduce dependence on solid fuels and the

subsequent prevalence of harmful household air pollution, via the production of clean burning biogas.

Designing a combined biodigester toilet thus establishes a self-contained waste management facility

which generates a clean burning modern fuel, and achieves the overall aim of the project.

3.3 Anaerobic Digestion

A biodigester here will be defined as a vessel in which anaerobic digestion takes place. The literature

relevant to the design and operation of a biodigester can be split into two major sections; the anaerobic

digestion process and existing biodigester technology.

Anaerobic digestion is a complex microbial process involving 4 chemical stages:

1. Hydrolysis: The chemical reduction of complex organic molecules (feedstock) into simple monomers

such as amino acids, fatty acids and simple sugars (Wang et al., 2007).

2. Acidogenesis: The bacterial breakdown of the simple monomers into volatile fatty acids (Wang

et al., 2007).

3. Acetogenesis: The bacterial conversion of volatile fatty acids into acetic acids. Carbon dioxide

and hydrogen sulphide are also produced in this stage (Wang et al., 2007).

4. Methanogenesis: The bacterial conversion of acetates into methane and carbon dioxide, the

primary constituents of biogas (Wang et al., 2007). It is also during this stage that the waste

stabilisation occurs, reducing odours and pathogenic concentration (Lettinga, 1995).


Oxygen toxicity occurs when oxygen molecules form free radicals in a cellular environment. These free

radicals are highly reactive and hence toxic to all cells. Unlike aerobic bacteria, anaerobic bacteria do

not possess the enzymes required to defend themselves against these free radicals (Parkin and Owen,

1986). It is therefore necessary for oxygen to be excluded from all stages of anaerobic digestion for

the processes to be performed correctly.

3.3.1 Feedstock

Feedstock for anaerobic digestion is the primary organic material which is broken down by the anaer-

obic bacteria. A number of factors such as the temperature, hydraulic retention time, pH, carbon

nitrogen (C/N) ratio and volatile solids (VS) content of the feedstock affect the rate of anaerobic

digestion. Manure from livestock such as cattle and pigs is commonly used as a feedstock. Systems

operating with these feedstocks are referred to as wet digesters as they require additional water to be

added. Dry digestion systems that do not require water also exist; these use plant based feedstock

such a coffee husks, maize, vegetables and purpose grown crops (Favre et al., 2009).

3.3.2 Anaerobic Digestion Products

The constituents of biogas produced by anaerobic digestion are outlined in Table 3.1. It can be seen

that methane and carbon dioxide are the primary constituents, contributing to approximately 95% of

the mixture. It is this high concentration of flammable methane which makes biogas useful as a fuel

source.

Table 3.1: Chemical constituents of biogas (Favre et al., 2009)

Gas Component Concentration Range Mean Value

Methane (CH4) 45-75% 60%

Carbon Dioxide (CO2) 25-55% 35%

Water Vapour (H2O) 0-10% 3-10%

Nitrogen (N2) 0.01-5% 1%

Oxygen (O2) 0.01-2% 0.3%

Hydrogen (H2) 0-1% <1%

Ammonia (NH3) 0.01-2.5mg/m3 0.7%

Hydrogen Sulphide (H2O) 10-10000mg/m3 <500mg/m3

The solid digested waste, known as effluent, is another useful by-product. Anaerobic digestion removes

a significant amount of pathogens from the primary feedstock leaving a product rich in nutrients (Mata-


Alvarez et al., 2000; Wang et al., 2007). The use of the biodigester effluent as a plant fertiliser has

resulted in substantial improvements to basic farming practices in many communities (Junfeng et al.,

2005).

3.3.3 Technical Factors

The rate at which anaerobic digestion is performed is dependent on a number of technical factors.

It is these factors which therefore determine the rate of biogas production and the extent to which

pathogen content is reduced, making them important considerations for the design and operation of

a biodigester.

Volatile Solids:

Volatile solids (VS) are the organic compounds which are reduced by the anaerobic digestion process,

the VS content can be considered the ‘digestible’ proportion of the feedstock (Wang et al., 2007). VS

reduction is often used as a measure of the extent to which anaerobic digestion has occurred. At a

constant temperature and pH, the biogas potential of a feedstock is primarily a function of its VS

content. Table 3.2 provides the VS% and biogas production potential of different waste feedstocks. It

should noted that this biogas potential is significantly influenced by animal diet; hence, actual values

of biogas production can vary significantly (Amon et al., 2007).

Table 3.2: Biogas production for different animal feedstocks (Junfeng et al., 2005)

Feedstock VS%Biogas Yield

(L/kg)

Daily Production

(kg/day)

Daily Biogas

Production (L/day)

Human 25 30 0.6 18

Cow 18 25 12 300

Chicken 20 100 0.1 10

Pig 20 25 2 50

As shown in Table 3.2, the average human will produce 18 L of biogas per day. It is estimated that

a single person in a developing nation requires between 150 to 300 L of biogas daily (Deublein and

Steinhauser, 2010). It is obvious that a population cannot be completely self-sustainable from the

energy provided by human waste, however it can make up a significant proportion of a populations

total energy demand.


Temperature:

For waste treatment purposes anaerobic digestion is typically performed in one of two temperature

ranges; mesophilic, between 30◦C and 38◦C, or thermophilic, between 49◦C and 57◦C. Each range

contains a different species of anaerobic bacteria that is responsible for the methanogenesis conver-

sion; mesophiles are present in the mesophilic range and thermofiles in the thermophilic range. Figure

3.1 shows that with decreasing temperature the time required to reach the maximum volatile solids

reduction is increased, indicating that lower temperatures result in a slower rate of anaerobic diges-

tion. Outside their respective temperature ranges, mesophile and thermophile activity reduces and

eventually ceases as the bacteria perish. It has been found that mesophiles are able to survive in

temperatures as low as 15◦C however the rate of digestion at these temperatures is negligible (Wang

et al., 2007).

Figure 3.1: Effect of solids retention time and temperature on volatile solids reduction in a laboratory

scale anaerobic digester (Wang et al., 2007)

Both mesophilic and thermophilic digestion extract roughly the same amount of biogas from feedstock,

however thermophilic reactions are faster due to a higher energy input (Vindis et al., 2009). Both

reaction types are also very sensitive to rapid temperature changes, suggesting a need for insulation

to dampen the effect of fluctuating temperatures (Chae et al., 2008).


Retention Time:

The retention time (RT) is the length of time the organic material remains within the system. The

required RT is directly related to the temperature inside the biodigester. Advanced multistage biodi-

gester designs achieve required retention times for maximum VS reduction as low as five days by using

the high temperature thermophilic process. Single stage mesophilic biodigesters such as those typically

used in the developing countries require a retention time between 30 and 60 days (Suryawanshi et al.,

2013).

pH:

pH affects the methanogenesis stage of anaerobic decomposition, which is most productive between

pH 6.8 to 7.5 (Environmental Protection Agency, 2012). Activities below a pH of 6 and above a pH

of 8 will hinder and potentially cease the digestion process (Karki and Dixit, 1984). During the initial

set up of an anaerobic reaction, when the acetogenesis stage is approaching completion, the acetic

acid produced can create conditions as low as pH 5.5 (Wang et al., 2007). This initial acidic period

is balanced after methanogenesis is complete and ammonia is produced, increasing pH (Wang et al.,

2007).

C/N Ratio:

If the ratio of carbon to nitrogen (C/N) in the feedstock is too high (> 60), nitrogen will be consumed

rapidly during the acidogenesis and acetogenesis stages, and will not be available to react with the

remaining carbon as required in methanogenesis (Parkin and Owen, 1986). If the ratio is too low (<

2), excess nitrogen will lead to a high concentration of ammonia thus increasing the pH which can

then inhibit methanogenesis (Parkin and Owen, 1986). The ideal C/N for the production of biogas

is 25, though ratios between 5 and 40 are acceptable (Parkin and Owen, 1986). Table 3.3 shows that

C/N ratios of cow and pig manure are close to the optimal value of 25. Humans and chickens have

lower C/N ratios that are still within the acceptable range.

Table 3.3: C/N ratio of some organic materials (Karki and Dixit, 1984)

Feedstock C/N Ratio

Human 8

Cow 25

Pig 18

Chicken 8


3.4 Biodigester Designs

An extensive range of biodigester designs currently exist, each for its own specific application. These

include large-scale processing plants for all types of biomass, medium-scale designs for farms or restau-

rants and small single-stage designs predominant in developing countries. The primary focus of this

review is the single-stage designs, as their simplicity and relatively low cost make them applicable in

developing regions of the world.

Small-scale designs vary in a number of different ways according to shape, size, complexity and ma-

terials. Nonetheless, it is possible to categorise most designs into one of three models; fixed dome,

floating drum or plug flow. Additionally, designs can be classified by their construction techniques;

prefabricated or permanent structure. On-site permanent biodigesters have historically been the most

reliable and widely implemented, however recent improvements in prefabricated technologies are seeing

the emergence of these as a viable alternative.

3.4.1 Fixed Dome

The fixed dome biodigester (Figure 3.2) is the most simple and reliable of the three major designs. It

originated the 1950s and is now common throughout China and Africa (Amigun and Stafford, 2011).

It usually consists of a cylindrical structure for waste storage with a dome-shaped gas collection area

situated above. A displacement pit is included to collect digested slurry. The design relies on pressure

created by the collection of biogas to force the slurry out of the digester and into the displacement

pit.

Figure 3.2: Fixed dome biodigester (Weir, n.d.)

Fixed dome digesters have an expected lifespan of 20 years as there are no moving parts or corrosion

prone surfaces, leaving few potential sources of failure (SNV, 2007). Cement and brick are the most

common construction materials, used for their durability and suitable thermal properties. Fixed

dome digesters are often buried underground, providing additional insulation and reducing spatial

requirements.


Amigun and von Blottniz (2010) note that the average cost of a fixed dome digester constructed in

South Africa is 860 USD, which is significantly cheaper than 1420 USD required for a floating drum

digester in the same location. Similarly in India the price for a 3m3 fixed dome system was 450 USD

cheaper than a floating drum digester of the same size (Singh and Sooch, 2002).

Construction is difficult and labour intensive, usually taking three people at least two days and requir-

ing the supervision of a qualified technician (Rwanda Utilities Regulatory Agency, 2012). Gas leakage

is also an issue as it is difficult to create a completely gas-tight environment from cement and brick.

Also, as the rate of biogas production from anaerobic digestion is not constant, the fixed volume for

gas collection provides a variable pressure output, complicating combustion applications.

3.4.2 Floating Drum

Floating drum biodigesters (Figure 3.3) are common in India, where over 4 million models are currently

in operation (Kaniyamparambil, 2011). The design consists of an underground chamber, similar to

that of the fixed dome digester, with a metal drum above. This drum moves up and down in a guiding

jacket depending on the volume of biogas held in the system.

As the volume of the gas collection system is able to adapt to the variable gas production a relatively

constant gas pressure can be achieved from this system which is desirable from a combustion perspec-

tive. The volume of gas held within the system can also easily be determined by the height at which

the drum is raised.

A floating drum biodigester is more expensive compared to fixed dome and plug flow digesters, pre-

dominantly due to the cost of the large metal drum. Regular maintenance adds additional costs and

labour that are not required for fixed dome or plug flow digesters. Rust must be removed from the

drum as well as regular painting to prevent corrosion. Dried slurry must be regularly removed from

the metal drum surface to ensure the drum can move freely. Even when these maintenance procedures

are adhered to, the average lifespan of a floating drum digester in tropical regions approximately five

years (SNV, 2007).


Figure 3.3: Floating drum biodigester (Thai Biogas Energy Company, 2008)

3.4.3 Plug Flow

Plug flow biodigesters (Figure 3.4) are plastic membranes, typically polyethylene, with length to width

ratios of approximately five (Mart’i-Herrero and Cipriano, 2012). Manure is transferred lengthwise

along the digester with no mixing between different heights or widths. In this way the ejected effluent

is guaranteed to be the most digested waste.

Figure 3.4: Plastic tube plug flow biodigester. Adapted from Energypedia (2014)

The advantage of plug flow digesters is that they are portable and inexpensive. The plastic membrane

is usually placed in a trench during operation and can be easily emptied and transported if required.

Xuan et al. (1997) estimates the costs of a 4 m3 plug flow digester to be 50 USD in Vietnam, which

is on average six to seven times cheaper than other local fixed and floating drum alternatives.

Polyethylene is weak and can be punctured easily by a number of means including a stray animals

(Mart’i-Herrero and Cipriano, 2012). Additionally, as top half of a plug flow digester is located


above ground, it is poorly insulated and susceptible to temperature fluctuations. Kanwar and Guleri

(1994) analysed the performance of a fixed dome and plug flow type biodigestser of the same capacity,

concluding that the daily average biogas production of the plug flow digester was 33% less than the

fixed dome.

3.4.4 Prefabricated Technologies Versus Permanent Structures

Permanent brick and concrete biodigester structures have been the most commonly implemented

biodigester systems since the inception of the technology, however portable, prefabricated designs are

emerging to offer solutions to the lack of related with traditional permanent designs. The motivation

behind these prefabricated biodigesters is to produce “...technically reliable, highly adaptable, easily

transportable, and reasonably priced” products (Cheng et al., 2014).

Specific situations where traditional biodigester technologies are inappropriate:

• Locations with high ground water levels, such as coastal areas where constructing on-site con-

crete, stone or brick digesters is difficult.

• Remote areas, such as mountain regions, where providing and transporting conventional con-

struction materials is difficult.

• Sites with inadequate conventional construction materials and a specialized labour force.

• Residential areas that are rebuilt as a result of land reform measures, thus affecting the perma-

nent site locations of conventional digesters.

These issues prompted the Chinese National Development and Reform Commission to release a report

on biodigester designs which concluded that “...traditional brick and concrete-based digesters do not

meet the requirements for commercialization and large-scale implementation, whereas prefabricated

biogas digesters are promising technologies for dissemination” (El-Mashad and Zhang, 2010). Cur-

rent prefabricated designs can be divided into two categories; bag digesters and composite material

digesters. Bag digesters are predominantly variations of the typical polyethylene plug flow digesters.

These biodigesters are more suited to rural areas where there is less chance of damage and greater

spatial availability (Cheng et al., 2014).

A common type of composite material digester is the fiber-reinforced plastic model (FRP). This model

is based on the fixed dome digester but its lightweight construction makes it portable and durable

with a high rate of productivity (Jiang et al., 2010). Currently the costs of these designs is high,

however with market growth and economies of scale this is expected to decrease substantially (Cheng

et al., 2014). A dismountable FRP is shown in Figure 3.5.


Figure 3.5: Dismountable FRP biodigester model (Cheng et al., 2014)

Another example of composite material digester is the modified water tank design (Figure 3.6). These

designs use existing water tanks to reduce costs yet still provide the portability and reliability of FRP

designs (Jiang et al., 2010).

Figure 3.6: Biodigester created from existing water tanks in Cambodia (Engineers Without Borders,

2011)

The ARTI model (Figure 3.7), created by an NGO in Maharashtra, India, is a composite material

digester based on the traditional floating drum digester. It uses cut-down high-density polyethylene

tanks for the digester and drum. The design costs only approximately 200 USD, significantly cheaper

than current steel and brick models, though currently the design can only be constructed on a very

small scale (ARTI, 2014).


Figure 3.7: ARTI bioidigester: A prefabricated plastic product based on the existing floating drum

design (Zu, 2005)

After review of the different biodigester models, it is obvious that prefabricated systems offer more

opportunities for implementation in the developing world over permanent fixed dome and floating

drum designs. They do not require large areas of land or holes to be created, and can simply be

transported to a particular location, and relocated when required. These advantages also extend to a

biodigester toilet system; a portable design would enable widespread implementation without the need

for large land areas or specialist construction techniques. The system could be constructed offsite by

an NGO or similar party, and provided to a community with little cost on available space.

3.5 Existing Biodigester Toilets

Currently, several successful combined biodigester toilet systems exist, although they are almost ex-

clusively permanent structure designs which share many of the disadvantages of traditonal permanent

biodigester technology. One such design was developed during an Engineers Without Borders (EWB)

challenge. A group of undergraduate students from the University of Adelaide designed and built a

portable biodigester toilet system, however it proved to be unsuccessful. It is clear there exists a lack

of successful, inexpensive and portable designs that incorporate both a toilet and biodigester with the

goal of providing a solution to unsafe sanitation and producing usable biogas.

3.5.1 Engineers Without Boarders Challenge (2011)

In 2011, a group of undergraduate engineering students supported by EWB were presented with a

series of health, energy and environmental issues that faced the village of Devikulam in India. It was

essential that their proposed solution to these issues be cheap, simple, safe, and have a positive impact

on the lives of the people of Devikulam. The team decided that a biodigester toilet system would


be a suitable solution to a lack of clean cooking sources and health issues related to open defecation

(Ashley et al., 2011).

The group’s final design (Figure 3.8) utilised two large (5.5 m x 1.8 m x 1.5 m) concrete and brick

tanks, emptied biannually. A slab with toilet facilities was placed over the top of these tanks, providing

a convenient location for waste disposal. The design also included an animal waste trough, so farm

manure could be disposed of in the same system. A large flexible membrane was used to collect the

biogas produced and the tanks were buried in the ground to provide insulation.

Figure 3.8: EWB Challenge biodigesting toilet (Ashley et al., 2011)

This design provides an excellent method of utilising both human and animal waste to produce biogas,

and addresses the issue of unsafe sanitation and its associated health problems by providing a toilet

facility. However, as the system is a permanent structure built from concrete and brick, it is still

restricted by the disadvantages of traditional biodigester technology, namely portability and space

requirements. While it addresses the needs of a single village it is not suitable as a global solution as

it cannot be easily manufactured and distributed throughout the developing world.

3.5.2 Adelaide University Honours Project 777 (2009)

In 2009, under the supervision of Dr. Steven Grainger and Dr. Colin Kestell, a group of Mechanical

Engineering students from The University of Adelaide designed and constructed a biodigester toilet

system. The overarching goal of the project was to effectively sanitise “human waste so that its effluent

is safe for reuse, producing a form of fuel that can be used to cook meals and aid in the daily lives of


users and must cost nothing to run.” (Coffee et al., 2009). The project team worked in conjunction

with two students from The University of Douala, Cameroon, and the system was designed to be

implemented specifically in this region.

The criteria guiding the design of the prototype were (Coffee et al., 2009);

• The system must fit in a highly populated environment

• The system must effectively treat human waste to reduce the spread of waterborne diseases

• There must not be any stagnant water that provides malaria carrying mosquitoes to breed

• A sustainable fuel that can be used for heating and cooking must be produced

• The system must not require electrical input for operation

• The system must be simple to operate

• The system must be inexpensive

The final design utilised two polyethylene water tanks, a series of plumbing and gas fittings and a

marine toilet. The two polyethylene water tanks served as the main anaerobic digestion chamber,

while the marine toilet utilised a manual pump to input waste into the system. The marine toilet

pump also allowed the toilet to be situated at ground level.

The biodigester used crushed bricks to increase the surface area available for anaerobic bacteria to

cultivate (Coffee et al., 2009; Stephenson, 1987). Two tanks were used to act as a baffle system,

increasing the retention time of the system (Coffee et al., 2009). The tanks could also be isolated, so

that the entire system was portable. To collect any biogas produced, both flexible membranes (Figure

3.9) and a floating drum style gasometer (Figure 3.10) were employed, both of which experienced

complications.


Figure 3.9: Prototype design with flexible membrane gas collection (Coffee et al., 2009)

Figure 3.10: Prototype design with gasometer gas collection (Coffee et al., 2009)

There were several issues with the design and testing procedure, which resulted in little biogas being

collected (Coffee et al., 2009):

• Biogas production was insignificant

• Conditions were too cold for anaerobic digestion (< 10◦C)

• Retention time was too short

• Hand pump for toilet was susceptible to clogging

• Flexible gas collection membrane continually leaked at seals and pipe connections


• Gasometer collection method created back pressure issues, driving biogas back into the system

Based on these issues the following improvements were suggested (Coffee et al., 2009):

• Insulating the system to control the internal temperature and promote anaerobic digestion

• Enlarging the system to increase retention time

• Use a solar water purification system for post-processing of effluent

• Investigate pre-processing of waste to prevent the pumps susceptibility to blockage

• Use purpose built tanks to prevent gas leaks

Honours Project 777 provided an excellent basis for the development of new biodigester toilet designs

by creating a portable and inexpensive design. However, significant improvements are required to

overcome the complications with the effectiveness of the design.

With consideration to the overall project aim, the best single solution to poor sanitation practices and

household air pollution is a combined biodigester toilet system. It provides a method of separating

excreta from human contact at the source, and produces clean burning biogas which can replace

solid fuels. The anaerobic treatment process significantly reduces the pathogens present within the

waste, and creates a safe product that can be used as a fertiliser. Different biodigester designs were

evaluated in Section 3.4, and it was concluded that prefabricated, portable biodigesters offer a number

of advantages over traditional, permanent structures. A review of existing biodigester toilet designs

revealed that although they do exist, many are not portable and require large, permanent structures.

The portable systems that do exist have not been effective, and significant improvements to their

design can be made. Based on the current state of technology, there is a clear need for the design and

construction of a portable biodigester toilet system.

Chapter 4

Scope, Objectives and Timeline

4.1 Scope

Through successful design, construction, and implementation, a biodigester utilising human waste as

a feedstock provides a stand-alone waste management facility that does not require a municipal waste

system. A biodigester toilet also provides a means of producing biogas for cooking, heating, and

lighting. Providing a waste management facility, and a means of producing biogas in one system will

improve the quality of life for millions of people in the developing world. Billions of people living in

wealthy countries enjoy the use of improved sanitation facilities and clean burning cooking gas, and a

biodigester toilet will enable citizens of developing nations to enjoy the same standard of living.

The scope of the project encompasses the design, build, and preliminary testing of a prototype biodi-

gester toilet system. Beyond these achievements, future work may involve developments to the design

or material selection for economic mass production, and implementation into developing communities.

This would be done in conjunction with the development of education programs detailing the correct

operation of a biodigester toilet, to maximise system effectiveness, and guarantee the safety of those

using the system.

4.2 Core Objectives

Objectives were formulated within the scope of the project and defined in a measurable manner for

assessment of project success. The objectives and measurements of success are listed below.

1. Design and build a portable toilet that meets the definition of a Shared Sanitation Facility,

as outlined by the WHO/UNICEF Joint Monitoring Program (JMP) for Water Supply and

Sanitation.

31

CHAPTER 4. SCOPE, OBJECTIVES AND TIMELINE 32

Measurement: If the system ensures hygienic separation of human excreta from human contact,

and is shared by the equivalent of two or more households (WHO and UNICEF, 2013), then this

goal will be achieved.

2. Include a functioning biodigester component in the design that is capable of harnessing the

human waste collected in order to produce biogas.

Measurement: The success of this goal will be based on the biogas production rate (litres of

biogas per kilogram of feedstock). A minimum numerical target of 10L per kg of feedstock was

set after reviewing literature on typical biogas production rates.

3. Integrate the toilet with the biodigester to create a portable biodigester toilet unit.

Measurement: The system will be designed to accommodate a toilet attached to the inlet

pipe. The system will also be disassembled, moved, and reassembled during the testing phase

to demonstrate portability.

4. Ensure the design is acceptable for implementation and use in Australia by adhering relevant

Australian standards.

Measurement: A detailed analysis of the design in regard to the relevant Australian standards

on sanitation and gas production and storage will be performed. Other relevant and insightful

standards will also be identified.

5. Demonstrate a viable use for the gas generated by the biodigester.

Measurement: The goal will be met if the application of biogas is successfully demonstrated

by the use of typical equipment such as a cook stove or lamp.

4.3 Extension Goals

1. Design and build a suitable cubicle to house the toilet.

Measurement: If a cubicle is designed and constructed to a suitable standard, determined by

qualitative analysis, then the goal will be met.

2. Research and design possible methods of effective post-treatment for both liquid and solid com-

ponents in order to ensure the effluent exiting the system poses no health or environmental

risks.

Measurement: Qualitative analysis of the effluent to detect pathogens and other harmful

components will be performed in order to ensure that it is of an acceptable quality.

CHAPTER 4. SCOPE, OBJECTIVES AND TIMELINE 33

4.4 Project Timeline

The timeline for the design and build of a biodigester was defined using a Gantt chart (see Appendix

A). This Gantt chart listed all major milestones and their due dates, as well as a strict timeline to be

followed by the team in order to achieve these milestones. Review gates were listed in a table (Table

A.1 in Appendix A). These review gates were designed to ensure that the team stayed up to date

with all requirements. Major milestones and their completion dates were also listed. These are shown

in Table A.2 of Appendx A.

Chapter 5

Design Formation

The design formation phase of the project involved identifying the requirements of the system for it

to provide the maximum benefit to the end user while meeting the core project objectives outlined in

Section 4.2. A list of design criteria was produced to assess the effectiveness of a design at meeting these

objectives. Several conceptual designs were proposed and evaluated against these design criteria.

5.1 Standards and Recommendations

To ensure the design was safe, effective and robust, it had to comply with relevant Australian standards.

Designing the system to Australian standards also ensured that it could be ethically implemented in

communities lacking in strict safety guidelines. Recommendations from a consultation report produced

for the Australian Pork Association provided a Code of Practice (CoP) for on-farm biogas production,

and use on piggeries (Davidson et al., 2013). These were followed for the project to ensure that all

relevent standards were met, and there were no major safety issues with the design. The CoP was

specifically written for biogas installations implemented in large-scale piggeries, therefore most of the

recommendations were irrelevant. A description of the standards relevant to a small scale biodigester

toilet are presented in Table 5.1. Additionally, the recommendations provided by the Australian Pork

Association CoP that could apply to the design and build of a small scale biodigester are shown in

Table 5.2.

34

CHAPTER 5. DESIGN FORMATION 35

Table 5.1: Relevant Australian Standards (Davidson et al., 2013)

Standard Description

AS 2885 (2008)

Applies to steel pipelines, and associated piping and components that

are used to transmit single and multi-phase hydrocarbon fluids, such as

natural and manufactured gas, liquefied petroleum gas, natural

gasoline, crude oil, natural gas liquids, and liquid petroleum products.

AS 4041 (2006)

Sets out minimum requirements for the materials, design, fabrication,

testing, inspection, reports, and pre-commissioning of piping subject to

internal pressure or external pressure or both. Specific requirements

are given for piping constructed of carbon, carbon-manganese, low

alloy and high alloy steels, ductile and cast iron, copper, aluminium,

nickel, titanium, and alloys of these materials.

AS 4130 (2009)

Specifies requirements for polyethylene pipes for the conveyance of

fluids under pressure. Such fluids include, but are not restricted to:

water, wastewater, slurries, compressed air, and fuel gas. Fuel gas

includes natural gas, liquefied petroleum gas (LPG) in the vapour

phase, and LPG/air mixtures.

AS/NZS 3814

(2010)

Provides minimum requirements for the design, construction, and safe

operation of Type B appliances that use town gas, natural gas,

simulated natural gas, liquefied petroleum gas, tempered liquefied

petroleum gas, or any combination of these gases either together, or

with other fuels.

AS 1375 (1985)

Sets out the safety principles relating to the design, installation, and

operation of industrial appliances that involve the combustion of gas,

or oil, or other fuel in air suspension, or the generation of combustible

vapours in such appliances. It is clear that both open and enclosed

flares are industrial appliances that involve the combustion of gas, so

AS 1375 is applicable to both.

AS 5601.1 (2010)

This standard contains the mandatory requirements, and means of

compliance for the design, installation, and commissioning of gas

installations that are associated with the use or intended use of fuel

gases such as natural gas, LP Gas, biogas, or manufactures gas.


Table 5.2: Relevant recommendations for biogas installations relating to a small scale biodigester toilet

(Davidson et al., 2013)

Relevant Area Recommendation

Materials selection,

digester design

Low levels of hydrogen sulphide present in biogas can corrode

some materials. All plastics are suitable for contact with manure,

however Polyvinyl Chloride (PVC) piping must be UV resistant.

Copper, and steel (with the exception of stainless steel) should

never be used.

SafetyDigesters must be fitted with a hydraulic pressure relief, and

vent stack or equivalent component.

SafetyWaste storage structures must be tightly sealed to avoid

exposure to effluent.

Safety, pipeline design

A shutoff valve must be included in front of any component that

utilizes the biogas (eg. Generators) in a gas line. This valve must

shut automatically when the component ceases operation.

Environmental

protection

Biogas installation must seek maximum recovery of methane

within the feedstock to prevent uncontrolled release to the

atmosphere.

Safety Biogas appliances must have the Gas Safety Certification Mark.

Environmental

protection

Biogas installation must have an emergency flare system. This

will prevent venting of biogas into the atmosphere. The flare

must be capable of handling the entire volume of biogas

contained within the digester.

Materials selection,

pipeline design, gas

storage

All plastics apart from PVC and Polypropylene (PP) can be

used for biogas storage and conveyance. PVC can be used if it is

UV resistant. PP can be used if no fat is present in effluent.

Copper, brass, butyl rubber, and steel (with the exception of

stainless steel) should never be used.

Safety, pipeline designBiogas pipelines should be operated at pressures less than 100

kilopascals (kPa) for transfer distanced of less than 4000m.

SafetyAll piping components subject to pressure above atmospheric

pressure must have a pressure relief valve.

Pipeline designPipelines transferring biogas must have a constant minimum

slope of 2%, and must have provisions for condensate removal.


SafetyNo open flames should be within six metres of plant, and

appropriate warning signs should be in place.

Safety, gas storage

Pressure free membrane bags fitted with condensate removal and

over-pressure release valves, located in the open, attached to the

ground and protected from damage with a suitable restraining

system are acceptable.

5.2 Overall Design Specification

The project objectives outlined in Section 4.2 determined the requirements necessary for the design to

meet. The toilet was to meet the WHO definition of a shared sanitation facility, as outlined in Section

2.1. Therefore, the system had to adequately separate faeces from human contact, and be designed for

shared use (WHO 2013). The system also had to incorporate a biodigester component that produced

biogas for use as an alternative to solid fuels, and be capable of safely storing this gas.

The biodigester and sanitation facility were required to be a single portable system that could be

easily transported, adressing the inherant problem with traditional fixed dome and floating drum

biodigesters which are typically permanent brick structures installed below ground level. A portable

system is particularly suitable for refugee camps (where construction materials are often in short supply

(Fenner et al., 2007)), building sites (which are typically only temporary sites), high-density urban

areas in developing countries without access to proper sanitation, and where large-scale infrastructure

redevelopment commonly occurs (Mara and Alabaster, 2008).

Post treatment of the feedstock was an important extension objective of the project. This encompassed

recycling any water remaining from digestion, and ensuring effluent exiting the system posed no health

or environmental risks. The anaerobic digestion process is typically sufficient to completely remove

most harmful pathogens from faecal matter (Masse et al., 2011). However, post treatment is necessary

to safely dispose of waste with a higher degree of certainty, especially in areas where disposal occurs

in waterways used for drinking sources.

5.3 Design Criteria

Design Criteria were employed to evaluate initial concept solutions and were fundamental in guiding

the design process for selection of the final design. The criteria were chosen and weighted to best

represent the needs and environmental conditions of the end user. To cover a wide range of possible

end users, it was assumed that the design would be implemented in developing communities. For


these regions, an appropriate technology approach was developed to accommodate a limited technical

understanding and resources available in these areas. There are a number of examples, such as in

Chinhoyi, Zimbabwe (Chinyama, 2013) and Dar es Salaam, Tanzania (Tumwine et al., 2002) where

large, traditional sewage systems were installed with help from external agencies. These facilities

could not be properly constructed and maintained by the local population, and were subsequently

abandoned. Thus, an appropriate technology approach was employed to avoid similar issues.

Focus on an appropriate humanitarian engineering approach to technology in developing countries has

gained prominence in recent years. Murphy et al. (2009) described it as technology that:

• Meets the essential basic needs of the end user

• Is sound and flexible

• Meets local capabilities through materials and resources

Following these ideologies ensured that end user’s dependence on external intervention would be

reduced, thus achieving a more sustainable solution. The following design criteria were chosen in

accordance with these principals:

Function

The ability of the biodigester toilet to effectively separate human waste from human contact

while producing meaningful amounts of biogas.

Cost

Cost must be minimised in order for it to be affordable for implementation in developing com-

munities.

Constructability

Materials required for the design should be sourced locally where possible. Construction must

also be possible with basic skills and without excessive labour.

Acceptability

The design must be easy and intuitive to use. It must also accommodate the existing cultural

practices of the end users.

Reliability

A reliable design enables the end user to be less dependent on external intervention for mainte-

nance, and more committed to ensuring long term use.

Portability

A portable biodigester toilet enables the system can be constructed off-site, or relocated if

required.


In order to quantify the extent to which a design met these criterion, a numerical score for each

criterion was given. An initial score of zero was assigned; if the design contained a feature giving a

major advantage or disadvantage to the criterion two points were added or subtracted respectively.

Similarly one point was added or subtracted for a minor advantage or disadvantage respectively. Each

criterion was considered equally weighted, and the individual criterion scores were added to produce

a final score for each design.

5.4 Essential Design Features

Before concept designs were generated, a number of design features were identified as being essential

to ensuring an effective design. These features were common to each concept design.

Growing Medium

Crushed bricks or similar materials increase the surface area on which anaerobic bacteria can

cultivate, creating a higher density of bacteria, in turn accelarating the anaerobic digestion

process (Stephenson, 1987). It is not essential that the growing medium be crushed bricks to

achieve this result, rather, any material that would sink to the bottom of the digester to create

a larger surface area would suffice. Crushed bricks were specified in this case as they are a low

cost material that is widely available.

Outlets

Outlets were to be included on the digester to release feedstock once it had undergone the diges-

tion process. These outlets were to be large enough to allow both solid and liquid components

to exit the system.

Inflatable Membrane

An inflatable membrane was to be used for gas collection. This is a simple and versatile collection

system that can easily be incorporated into any design. It is also portable, greatly simplifying

the process of extracting gas samples for analysis. Considering practical applications of the

gas, portability is desirable as the gas will likely be more useful at a location separate to the

biodigester toilet. A disadvantage of inflatable membranes is that they are easily damaged and

require additional protection to reduce the risk of leaks.

Biodigester Type

As discussed in Section 3.4.3, plug flow digesters are inferior to fixed dome and floating drum

models in terms of biogas production and thus were immediately eliminated from design consid-

eration. Poor insulating properties result in a requirement of external heat addition to maintain

conditions favourable for anaerobic digestion. The fragile nature of a polyethylene bag system


also contributed to this decision, as the design is intended for rural, developing communities,

where free roaming livestock is common, and the risk of puncture is likely. These factors indi-

cate that the plug flow biodigester model is not suitable at achieving the project aim as poor

biogas production will not reduce dependence on solid fuels. Thus, fixed dome or floating drum

digesters are the remaining suitable types to be considered.

5.5 Conceptual Designs

After a set of design criteria and essential design features were identified (Sections 5.3 and 5.4), four

concept designs were created. These concepts varied in regards to the location of waste input and

toilet, the number of digestion vessels, and the implementation of either fixed or floating drum sub-

systems.

5.5.1 Concept Design 1

Figure 5.1: Concept Design 1

The first concept design (Figure 5.1) utilises a single tank to digest the waste in a fixed dome. When

compared to a dual tank system, a single tank reduces both cost and construction complexity as fewer

parts and less space is required. It features an inlet pipe that starts at the top of the tank and continues

to the base. This bottom feeding system allows the new waste to flow directly to the anaerobes on


the growing medium at the base of the tank, while the older semi-digested waste is pushed upwards.

Bringing the fresh waste in contact with the bacteria present on the growing medium allows for more

effective gas production (Stephenson, 1987). Additionally the bottom feeding pipe, if always below

the liquid level, will prevent gas flowing back up the inlet. The additional length of pipe increases the

risk of blockages.

The toilet is located at the base of the digestion tank, which is desirable in terms of accessibility,

but will require a pumping mechanism to transport the feedstock to the inlet pipe at the top of the

digestion tank. This complicates construction, maintenance, and adds to costs. The evaluation of this

design in regards to the design criteria is shown in Table 5.3.


Table 5.3: Concept Design 1 design criteria analysis

Criteria Concept Design 1

Function (-1)• Single tank does not allow settling of solid and liquid components for

water recycling (-2).

• Biogas output from a fixed dome is of variable pressure, causing difficul-

ties with combustion (-2).

• Bottom feeding inlet pipe reduces gas back-flow issues (+2).

• Bottom feeding inlet accelerates gas production (+1).

Cost (0)• Single tank reduces number of parts required and costs (+1).

• Requires pumping mechanism (-1).

Constructability

(+1)• Single tank requires fewer parts reducing construction time (+2).

• Pump complicates construction (-1).

Acceptability (0)• Pump requires maintenance and power (-2).

• Single tank requires less space (+1).

• Toilet at ground level is desirable (+1).

Reliability (+1)• Fewer tank connections reduce potential leaks (+1).

Portability (-2)• Single large tank more difficult to transport than two smaller tanks of

the same combined size (-2).

Total (-1)




The second concept design (Figure 5.2) is a two tank system. The use of two tanks increases the

portability of the design, as it is easier to transport two small tanks as opposed to a single large tank

of the same volume. The second tank also allows for the settling of solid and liquid components of

the feedstock to subsequently be treated by a water filtration system. The filtered water can then be

recycled for use in flushing the toilet or safely released into the environment.

The toilet is located at ground level with the inlet pipe entering at the base of the digestion tank. This

method has the advantages of directly feeding the waste into the anaerobes on the growing medium,

and preventing gas flowing back out of the toilet. It also minimises the increased risk of blockages that

existed in Design Concept 1 by reducing the length of inlet pipe. As the feedstock inside the digestion

tank will be above the water level of the toilet, feedstock backflow issues will need to be overcome.

The process involved with this second conceptual design is as follows:

1. The inlet pipe takes the feedstock to the bottom of the first tank.

2. Gas collects at the top of this tank and flows into the collection system.

3. After half the total retention time of the system has passed, the valve connecting the two systems

is opened, and the effluent is allowed to flow into the second tank.

4. The waste is stored in the second tank for the same duration that it is stored in the first,

completing the total retention time of the system. The second tank is also used as a settling

tank for the liquid to then be collected in the filtration system.

5. While the original effluent is being treated in the second tank, the first tank is refilled through


daily use. The first tank will fill once the second tank digestion has completed the designed

retention time.

6. Once the retention time is reached, the sedimentation tank is emptied. The connecting valve

between the two tanks is then opened to allow waste to flow into the now empty second tank

and the cycle continues.



Function (+1)• Second tank allows for implementation of settling and filtration system

(+2).



• Filtration system allows water to be recycled (+2).

• Inlet pipe may cause backflow issues (-2).

Cost (-3)• Two tanks require additional fittings (-1).

• Filtration system is expensive (-2).

Constructability

(-2)• Filtration system is diffucult to construct (-1).

• Additional connections for dual tanks increase construction time (-1).

Acceptability

(+1)• Filter requires frequent maintenance (-2).

• Reduced water input (+2).

• Toilet at ground level is desirable for user (+1).

Reliability (-1)• Extra connections increases likelihood of gas and liquid leaks (-1).

Portability (+2)• Two small tanks more portable than one large tank (+2).

Total (-2)




The third conceptual design is a dual tank system, however it differs from Concept Design 2 as the

second tank is a floating drum design used as a secondary digestion tank and gas storage vessel. The

major advantage of the floating drum tank over the fixed drum is constant gas pressure which is ben-

eficial for gas burning applications. The floating drum increases the complexity of both construction

and maintenance, as the drum is required to rise and fall freely with varying gas production. Gas

backflow issues can also arise with a floating drum collection system as identified in Section 3.5.2 due

to the weight of the floating drum, which has the potential to push the gas back into the first tank.

The secondary tank in this design still allows for the settling and potential recycling of the liquid

component of the feedstock.

In this design, the toilet and inlet are located at the top of the first digestion tank. This may introduce

some acceptability issues as users would prefer the toilet be at ground level, however it does provide

the major advantage of gravity feeding waste into the system which removes the need for any pumping

mechanism. A support framework would be required to support both the user and toilet on top of the

digestion tank, adding to costs. The process involved with this conceptual design is as follows:

1. Feedstock enters the first tank through the inlet tube.

2. Biogas is generated and collected in the first tank.

3. When the feedstock reaches a certain height in the tank, it is released into the second tank.

4. Gas is passed onto the second tank through a pipe connecting the tops of both the tanks.


5. The second tank is a floating drum design that accepts feedstock through the outlet pipe of the

first tank.

6. Biogas is generated in the same method as the first tank. As the level of gas in the tank increases,

the floating drum rises until it reaches the maximum level.

7. At this point, the gas in both the tanks is assumed to be filled to capacity. A gas pipe with a

valve is present at the top of the second tank to release the gas for practical use.

8. The feedstock in the second tank can be released through an outlet pipe, and the effluent can

be used as a fertiliser following the same concept as a composter.




Function (+5)• Second tank allows for potential implementation of settling and filtration

system (+2).

• Floating drum provides constant gas pressure for constant gas combus-

tion (+1).

• Feedstock can be gravity fed into system (+2).

Cost (-3)• Dual tanks require additional connecting parts (-1).

• Floating drum is more expensive than fixed dome (-1).

• Infrastructure required for mounting toilet (-1).

Constructability

(-2)• Construction is complicated by floating drum (-1).

• Requires additional infrastructure to support toilet (-1).

Acceptability (-1)• Complicated maintenance of floating drum (-1).

• Toilet is difficult to access at the top of the digestion tank (-1).

• Constant gas pressure simplifies gas combustion (+1).

Reliability (-3)• Extra connections increase likelihood of leaks (-1).

• Greater risk of failure in floating drum compared to fixed dome (-1).

• Floating drum introduces potential gas backflow issues (-1).

Portability (+2)• Two small tanks easier to move than one large tank (+2).

Total (-2)




Concept Design 4 is a dual tank, fixed dome system, with the addition of a stirrer to the first digestion

tank. The stirrer breaks up the layer of scum that forms on the surface of the feedstock inside the

tank. This scum layer forms a physical barrier between the gas production at the base of the tank and

the gas collection at the top of the tank. By rotating the stirring arm this layer is disturbed, enabling

the free flow of gas within the system. Construction and installation of the stirrer would require some

technical skill and knowledge, and also increase costs.

The toilet on this design is located at ground level with an inlet pipe entering at the top of the first

digestion tank. This inlet method requires a pumping mechanism, but simplifies construction as no

pipe needs to be installed inside the digestion tank. As the inlet pipe does not extend below the liquid

level, gas flowing back through the toilet is a possible hazard associated with this design.




Function (+2)• Second tank allows for settling and potential implementation of filtration

system (+2).



• Inlet pipe may cause gas backflow issues (-1).

• Stirrer increases biogas yield (+2).


• Stirrer is expensive (-2).

• Pumping mechanism required (-2).

Constructability

(-2)• Stirrer is diffucult to construct and install (-2).

• Additional connections for dual tanks increase construction time (-1).

• Simplified construction of inlet pipe (+1).

Acceptability

(+1)• Increased biogas yield for practical applications (+2).

• Toilet at ground level is desirable for user (+1).

• Pump requires maintenance and power (-2).


Portability (+2)• Two small tanks more transportable than one large tank (+2).

Total (-3)

5.5.5 Concept Selection

A summary of the evaluation of the concept designs can be found in the evaluation matrix (Table 5.7).

Considering this table alone indicates that Concept Design 1 is the most appropriate although still

a poor performer in functionality, portability, and acceptability. Furthermore, there was no standout

candidate that addressed all criteria.


Table 5.7: Evaluation matrix

Criteria CD* 1 CD 2 CD 3 CD 4

Function -1 +1 +5 +2

Cost 0 -3 -3 -5

Constructability +1 -2 -2 -2

Acceptability 0 +1 -1 +1

Reliability +1 -1 -3 -1

Portability -2 +2 +2 +2

Total -1 -2 -2 -3

*CD: Concept Design

As no individual concept design addressed all criteria effectively, the design features that varied be-

tween concept designs were analysed independently to develop an optimal system configuration. A

summary of the positive and negative design aspects can be found in Table 5.8. This table was used

to determine the optimal aspects of each concept design, and develop a hybrid final design based on

these positive features.


Table 5.8: Design feature summary table

Design Feature Options Positive Negative Score

Waste inputTop

Less blockage (+2)

Less parts (+1)

Simple construction (+1)

Gas backflow (-2) +2

BottomAnaerobe contact (+1)

No gas backflow (+2)Blockages (-2) +1

Toilet locationTop of tank Gravity fed waste (+2)

Accessibility (-1)

Infrastructure (-2)-1

Ground level Easily accessible (+1)Pump (-2)

Power input (-2)-3

Digestion tanksOne

Simpler construction (+1)

Reduced cost (+1)

Less space (+1)

Less sources of leaks (+1)

Less portable (-2)

No settling tank (-2)0

TwoIncreased portability (+2)

Settling tank (+2)

Construction (-1)

Increased cost (-1)

Leak issues (-1)

+1

Biodigester modelFixed dome

Simple construction (+1)

Less maintenance (+1)Variable gas pressure (-2) 0

Floating drum Constant gas pressure (+1)

Gas backflow issues (-1)

Construction (-1)

Maintenance (-1)

-2

Stirrer - Increased biogas yield (+2)Expensive (-2)

Construction (-2)-2

Water filter - Reduces water use (+2)

Expensive (-2)

Construction (-1)

Maintenance (-2)

-3

Based on Table 5.8 the following decisions were made:

• The toilet will be located at the top of the digestion tank to eliminate the need for a pumping

mechanism.

• Waste will be fed to the bottom of the tank from an inlet at the top of the tank to ensure fresh

feedstock is in direct contact with the anaerobes, and to eliminate gas backflow issues.


• Two tanks mounted on pallets will be used to increase the portability of the system, as well as

providing the option for water recycling through the use of a settling tank.

• Fixed dome digestion tanks will be used to simplify construction and maintenance, and eliminate

gas backflow issues associated with fixed dome digesters.

• A water filtration system and stirrer will not be included in the final design due to the increased

difficulty in construction, costs, and maintenance incurred if included.

These decisions were used to produce the Final Concept Design (Figure 5.5).

Figure 5.5: Final concept design

The final concept design was subsequently evaluated using the same method performed on the original

concept designs (Table 5.9). This design received a higher overall rating compared to the original

concept designs and formed the basic layout of the final design.


Table 5.9: Final concept design design criteria analysis

Criteria Final Concept Design

Function (+5)• Second tank allows for settling and potential implementation of filtration

system (+2).



• Bottom feeding inlet pipe reduces gas back-flow issues (+2).

• Bottom feeding inlet accelerates gas production (+1).

• Feedstock can be gravity fed into system (+2).


• Infrastructure required for toilet (-1).

Constructability

(-2)• Additional connections for dual tanks increase construction time (-1).

• Requires additional infrastructure to support toilet (-1).

Acceptability (-1)• Toilet is difficult to access at the top of the digestion tank (-1).


Portability (+2)• Two small tanks more transportable than one large tank (+2).

Total (+1)

Chapter 6

Final Design

After the preliminary layout was completed in the design formation phase (discussed in Chapter 5),

available resources for the final design were considered. Necessary components were identified based

on the resources and budget available including appropriately sized tanks, pipe fittings, and a gas

collection system. Based on the tank sizes available for the digester, the number of people able to

use the system was determined. An analysis was performed to identify the correct materials to use,

in order to prevent corrosion and degradation from the feedstock and biogas. Analysis on available

piping material was performed according to AS/NZS 4130 and AS/NZS 4645 to calculate the maximum

allowable operating pressure (MAOP) of the gas network, and a safe operating procedure (SOP) was

developed to ensure the system would never exceed this pressure. A stirring mechanism was also

designed and constructed using basic metal fabrication techniques, and made out of easily sourced

materials.

6.1 Final System Sizing

After receiving sponsorship from Barrow and Bench Mitre 10 Malvern two Maxiplas 1000L round

polyethylene rainwater tanks became available at a significantly reduced cost. In the interest of begin-

ning the construction and testing phase of the project as soon as possible, these tanks were purchased

as soon as they became available. With these fundamental components sourced, specifications were

calculated in regards to the end user.

6.2 Number of End Users

After the tanks were identified, the number of people able to use the system was determined in order

to verify that the design could be considered a WHO Shared Sanitation Facility, as outlined in Section

54

CHAPTER 6. FINAL DESIGN 55

4.2. Variables considered include:

• The number of people who will use the biodigester daily

• The average amount of waste produced daily by humans

• The ideal retention time for the waste in order to generate the most biogas

• The number of tanks available

• The volume of the tanks available

It was found that that an average person produces approximately 500 kgs of urine and 50 kgs of faeces

every year (Heinonen-Tanski and van Wijk-Sijbesma, 2004). From this yearly output, the weight of

urine and faeces produced by humans in a day was calculated. Note, as a biodigester toilet can be

implemented in a number of different regions, these numbers are subject to change depending on local

diet and conditions.

Average Fecal Matter Produced Per Day =50 kg

365.25day= 0.137

kg

day(6.2.1)

Average Urine Produced Per Day =500kg

365.25day= 1.37

kg

day(6.2.2)

Human urine has a specific gravity of between 1.002 and 1.035 (Ferreira, 2005); using the average of

these values, the density of the human urine could be calculated.

ρurine = Specific Gravity× 1000kg

m3 (6.2.3)

= 1.02× 1000kg

m3

= 1020kg

m3

The total daily liquid input to the system is the sum of flushing liquid from the toilet and human

urine. It was assumed that each person delivers their total daily waste in a single use of the toilet. A

common half-flush toilet uses approximately three litres of water per flush (Department of Industry,

2014). For the following calculations, the number of daily users of the toilet will be represented as

U.

Total Liquid Waste = (3L×U) +

(U× 1.37kg× 1m3

1020kg× 1000L

m3

)(6.2.4)

= 4.34×U (Litres)


The average density of human faeces is approximately 1000 kg/m3 (Ferreira, 2005). Therefore, the

total daily volumetric input to the system could be calculated from the sum of the solid and liquid

components in the feedstock.

Total Daily Input = (4.34×U) +

(0.137kg×U× 1m3

1000kg× 1000L

m3

)(6.2.5)

= 4.48×U (Litres)

It is now possible to determine the volume of the digestion tanks required to achieve the minimum

retention time of 30 days for steady state gas production (Suryawanshi et al., 2013). This volume is

determined as a function of the number of users of the toilet.

Volume of Digestion Tanks = 30days× Total Daily Input (Litres) (6.2.6)

= 30× (4.48×U) Litres

= (134.4×U) Litres

As discussed in Section 6.1, a total system volume of 2000L was acquired (two 1000L tanks). Using

Equation 6.2.6, the number of people able to use the system whilst achieving the minimum retention

time of 30 days could be calculated.

2000 = 134.4×U (6.2.7)

=⇒ U =2000

134.4

=⇒ U = 14.88

Therefore, 14 people are able to use the system. Current census data from India and China indicates

that the average number of permanent residents per household in rural areas is 5.4 and 3.88, respec-

tively (National Bureau of Statistics of China, 2013; The Registrar General & Census Commissioner,

2011). As a group of 14 people can be considered larger than an average household, the system can

be defined as a WHO Shared Sanitation Facility (WHO and UNICEF, 2014b).

6.3 Materials Selection

Based on the CoP for biogas production and use in piggeries produced for Australian Pork by Davidson

et al. (2013), tank structures can be constructed from all plastics, most stainless steels, clay, and


concrete. This information is presented in Table 5.2. The tanks offered by Barrow and Bench Mitre

10 Malvern were polyethylene. Using polyethylene tanks ensured that any modifications required

would be easier to perform than on a stainless steel tank. Stainless steel tanks are also significantly

more expensive than equivalent polyethylene water tanks. For any pipes carrying feedstock, UV

stabilised polyvinyl chloride (PVC) was chosen, again based on the information presented in Table 5.2.

The added advantages of using PVC piping are the standardisation of fitting sizes, low cost, and wide

availability; thus addressing the design criteria of ease of assembly and maintenance outlined in Section

5.3. For all pipes conveying biogas, polyethylene was chosen as the appropriate material, based on the

information presented in Table 5.2. The fittings chosen to connect the biogas pipeline were constructed

from a UV stabilised polypropylene copolymer. A UV resistant PVC biogas collection membrane,

purchased from Shenzhen Puxin Technology Co. Ltd, was chosen to capture any biogas produced.

Shenzhen Puxin is a Chinese manufacturer and trading company, specialising in medium and large

sized biogas systems and accessories. Based on Table 5.2, UV resistant PVC was a suitable material

for biogas storage. Neoprene rubber was used to create any seals required, due to its satisfactory

resistance to CH4 and CO2 (MykinInc, 2014).

6.4 Waste Collection System

After the two 1000L polyethylene tanks were purchased, final system dimensions and components

were determined. During the preliminary design stage, final sizing of the system was impossible as

no decision had been made on the exact tanks that were going to be used. Components of the waste

collection system that had to be finalised included the waste inlet, tank lids, connection between the

two tanks, and effluent outlets. The decisions pertaining to these components were made based on

the concept design selection in Section 5.5.5. The final design process was simply an extension of the

work undertaken in the design formation phase, where the two-tank system mounted on pallets was

selected. Final drawings of the system and dimensions are presented in Appendix B.

6.4.1 Inlet Design

To prevent gas flowing out of the first tank through the feedstock inlet, the inlet pipe was extended

1200 mm downwards into the first tank, so that its opening was always below the liquid level. This

liquid seal prevented gas flowing up through the inlet pipe, and back out of the system; important

when considering the end user of the biodigester toilet. When implemented, flammable gas flowing

back through the inlet and out of the toilet would create a serious safety issue. Figure 6.1 shows the

inlet pipe assembly. A drawing of the inlet assembly installed in the first tank can be seen in Appendix

B.


Figure 6.1: Drawing of inlet assembly (dimensions in mm)

6.4.2 Toilet Choice and Location

100 mm diameter sewerage grade PVC pipe was added to the top of the first tank, and was part

of the overall inlet assembly. This pipe enabled the connection of a toilet bowl to the top of the

first tank. By having the toilet mounted above the system, water could simply be poured into the

bowl to flush waste into the first tank. Using gravity to drop the waste into the tank, removed the

need for a pumping mechanism. The location of the toilet bowl then allowed for two potential design

modifications. Either a frame with stairs could be built to allow access to the toilet, or the tanks

could be buried in holes within the ground, thus placing the toilet at ground level. Burying the tanks

would provide added insulation to the system, making implementation in colder climates possible, but

would hinder the portability.

6.4.3 Lid Design

At the time of purchase, both tanks contained large holes at the top. Lids were designed and con-

structed to make the system as airtight as possible. In similar systems, the tanks would need to be

checked for holes and leaks prior to operation to ensure the digestion process occurs in the absence


of oxygen. The first tank contained a 365 mm diameter hole, and the second tank contained a 180

mm diameter hole. Two sections of 6 mm thick neoprene rubber were compressed over the holes

using 7 mm exterior grade plywood, stainless steel screws, and exterior grade silicon sealant. On the

second tank, an off-cut of polyethylene was used as an extra layer of compression. Holes were cut

in the rubber, plywood, and plastic, and 25 mm diameter tank flanges and compression fittings were

attached to provide connection to the gas pipe network. The assembled lid for the second tank in the

system can be seen in Figure 6.2. The attached gas fittings for the first and second tanks are shown

in Figures 6.3 and 6.4, respectively. Detailed drawings for the lids and gas connections can be found

in Appendix B.

Figure 6.2: Final attached lid for second tank in the system


Figure 6.3: First tank attached gas connection

Figure 6.4: Gas connection valve on second tank

6.4.4 Increasing Digestion Surface Area

To provide an increased surface area for the anaerobic digestion process to occur, plastic bioballs,

similar to those used in aquariums, were placed in the bottom of the first tank. These bioballs acted


as a growing medium for the anaerobic bacteria. Although the concept designs outlined in Chapter 5

all utilised crushed bricks at the bottom of the digester to increase the surface area, bioballs were used

in the final design to prevent blockage of the outlet taps. The two tanks acquired from Barrow and

Bench Mitre 10 Malvern, contained 25 mm diameter threaded holes just above their bases. Because

the hole was already threaded, taps were simply installed into the tanks, as discussed in Section

6.4.6. Because of this outlet diameter, crushed bricks had the potential to block the hole. However,

crushed bricks could still be used if these holes were larger; an important consideration to make when

implementing this system in a developing community without access to aquarium supplies. Figure 6.5

is an example of a typical bioball. The increased surface area provided bacteria a location to grow

and produce a ‘biofilm’. Feeding the feedstock to the bottom of the tank brings it into direct contact

with this biofilm, making the anaerobic digestion process more effective (Stephenson, 1987).

Figure 6.5: A typical bioball shape (Foster and Smith, 2014)

6.4.5 Tank Connection Design

As discussed in Section 5.5.5, it was decided that the two tanks would be connected to allow feed-

stock transfer, increase portability, and provide a means of solids settling for potential effluent post-

treatment. Locating the transfer point 860 mm above the base of the tanks was done for two main

reasons; to ensure mostly liquid was transferred to the second tank to allow for solid settling, and

to prevent the bioballs at the bottom of the first tank from entering the transfer pipe. Reducing

the amount of solid feedstock transferred to the second tank would reduce the time required for sus-

pended solids to settle. Clarification of the effluent via settling in the second tank was a precursor

to post-treatment of the effluent. Although post-treatment of the effluent was outside the scope of

this project, it was still important to design the system so that this could be implemented in future

work.


To prevent blockage by the feedstock, the diameter of the transfer pipe and fittings was 50 mm. PVC

suction hose was used as the transfer pipe, due to its flexibility. When connecting two small tanks

together, there is risk of one being knocked or moved out of place. If a rigid connection is used

between two tanks and any movement occurs, there is significant chance of the transfer pipe cracking,

and effluent spilling from the system. Flexible suction hose allows for some movement and will not

crack. After inspection of the hose, it was deemed that a 500 mm length provided enough flexibility

to allow for some movement of the tanks.

Suitable sized holes were created in the two tank walls using a hole saw and drill, and 50 mm diameter

PE tank flanges were attached, with two layers of neoprene rubber on either side of the tank wall to

provide an extra level of protection from leaks. The flanges were tightened from both sides of the tank

wall, compressing the neoprene rubber and forming a tight seal. The attached flange can be seen in

Figure 6.6.

Figure 6.6: Attached tank flange with neoprene seal

A 50 mm internal diameter ball valve was attached to each tank flange. Having a valve on each tank

allowed both tanks to be isolated, providing the ability to remove the connection between the tanks

and move them individually. Plumbing thread tape was used to create a leak-proof seal at the mating

point of the tank flange and the ball valve.

50 mm internal diameter PE barbs were then attached to the ball valves. Again, thread tape was

used to create a leak-proof seal at the mating points of the ball valves and the barbs. These barbs

provided an attachment point for the 50 mm diameter suction hose. The suction hose was forced onto

the barbs with an interference fit, and stainless steel hose clamps were used to secure the hose to the

barbs. Figure 6.7 shows the connection without the suction hose attached. The connection with the

suction hose attached can be seen in Figure 6.8, and the overall tank connection system can be seen in

Figure 6.9. Subsequent testing outlined in Section 9.2 with clean water confirmed that this connection

had no leaks.


Figure 6.7: Attached ball valve and barb

Figure 6.8: Attached ball valve, barb, and suction hose

Figure 6.9: Overall connection between two tanks

6.4.6 Outlet Design

Both digestion tanks came with a 25 mm female threaded fitting, approximately 100 mm above the

base. A 25 mm tap was connected to each of these fittings, using a 25 mm diameter brass nipple,


and a section of brass threaded rod to extend the tap over the edge of the pallet. Thread tape and

silicon was used to seal the mating point. These taps allowed for the drainage of effluent from both

tanks. Hose fittings were attached to the taps so that the effluent stream could be directed. Figure

6.10 shows the outlet fitting layout.

Figure 6.10: Outlet tap attached to existing 25 mm diameter threaded hole

6.5 Gas Collection System

A simple layout was devised for the gas piping and connection network to ensure it could be maintained

and modified with ease. 20 mm diameter polyethylene pipe was used between the two compression

fittings situated at the tops of each tank. These fittings and their attachment methods were explained

in Section 6.4.3. Gas rated thread tape was used to create a seal at all mating points between the

fittings. Reducing nipples were used to make the 20 mm diameter piping compatible with the 25 mm

fittings.

The gas collection membrane had a 20 mm diameter threaded fitting, that allowed a ball valve and

compression fitting to be attached directly. This connection is shown in Figure 6.11. A length of

pipe was installed between the second tank and the gas collection membrane. The valve connected to

the collection membrane allowed it to be isolated from the system, enabling gas samples to be taken

with ease. Once the valve was shut, the compression fitting could simply be unscrewed, and the pipe

removed from the membrane.


Figure 6.11: Connection between gas collection membrane and pipe network

6.5.1 Pipe Network Pressure Analysis

Calculations were performed according to Australian standards to determine the Maximum Allowable

Operating Pressure (MAOP) of available polyethylene piping material. 20 mm nominal outer diameter

polyethylene pipe was available at Barrow and Bench Mitre 10 Malvern. The dimensions and properties

of this pipe are outlined in Table 6.1. Note, the minimum wall thickness and minimum mean outside

diameter were determined in accordance with tables provided in AS/NZS 4130 (see Appendix C). The

value of maximum required strength (MRS) for PE100 polyethylene pipe was determined from AS

4645.3. These values were required for calculating the MOAP for this particular polyethylene pipe,

using the method outlined in AS/NZS 4645.3.

Table 6.1: Properties of PE100 pipe

Property / Dimension Value

Nominal outer diameter 2 0mm

Long term rupture stress rating PE100

Pipe pressure rating PN12.5

Standard dimension ratio (SDR) 13.6

Maximum required strength (MRS) 10 MPa

Minimum wall thickness (Tmin) 1.6 mm

Minimum mean outside diameter (Dm min) 20.0 mm

Using Table B1 in AS/NZS 4645.3, the design factor (C) was determined for the pipe. This table is

shown in Appendix D. Several operational conditions for the system had to be assumed to correctly


use the table. Based on the information presented in Table 3.1, it was assumed that biogas had a

similar composition to natural gas (majority methane) for the purpose of this analysis. Also, based

on average maximum temperatures for Adelaide throughout September and October (19.1◦C and

21.9◦C respectively) (Bureau of Meteorology, 2014), it was predicted that the maximum operating

temperature within the greenhouse would never exceed 40◦C. Finally, as the prototype was to be

located on the Urrbrae Agricultural High School campus, it was assumed to be operating in a “high

density community use” area. These assumptions allowed the determination of index values f0, f1, f2

and f3 to be used to calculate C. Equation 6.5.1 was used to calculate C, and was sourced from Table

B1 in AS/NZS 4645.3 (Appendix D).

C = Design Factor (6.5.1)

= f0 × f1 × f2 × f3

= 2.0× 1.3× 1.1× 1.2

= 3.43

After the design factor was calculated, the MAOP was calculated according to the equation provided

by AS/NZS 4645.3 for polyethylene mains and service pipes (Equation 6.5.2).

MAOP =2×MRS× Tmin

C× (Dm min − Tmin)(6.5.2)

=2× 10× 1.6

3.43× (20.0− 1.6)

= 0.507MPa

A MAOP of 0.507MPa (approximately five times greater than atmospheric pressure) was deemed to be

a suitable operating pressure for the gas network. The system would be providing biogas for cooking,

heating and lighting daily, meaning that the pressure would constantly be released. After determining

the MAOP of the pipeline was suitable, the only other points of failure within the gas network then

became the fittings between the gas pipes, and the biogas collection membrane.

6.5.2 Pipe Fitting Pressure Analysis

After calculating the MAOP of the pipeline, it was necessary to determine whether fittings available

at Barrow and Bench Mitre 10 Malvern for the biogas pipe network could withstand the pressure

developed within the system. The available fittings were Poly16 Plus Compression Fittings, manu-

factured by Alprene Plastic Products Pty Ltd. Technical data available on the Alprene website listed


the fitting pressure rating as PN16 (Alprene, 2014); meaning that the fittings had a nominal working

pressure of 1.6 MPa. As this nominal working pressure is greater than the MAOP of the pipe network,

these fittings were deemed appropriate for connecting the 20 mm PE pipes.

6.5.3 Biogas Collection Membrane Pressure Analysis

The biogas collection membrane purchased from Shenzhen Puxin Technology Co. Ltd was a 1m3 PVC

membrane, with a single 20 mm diameter threaded fitting. Figure 6.12 shows the actual membrane

used in the prototype.

Figure 6.12: 1m3 biogas collection membrane used in the final design

No information was available on the MAOP of the membrane. From a safety perspective, this is a

signficiant issue; hence it was decided to investigate the worst case scenario for the MAOP of the

membrane to determine a SOP to prevent it bursting. The worst case scenario for the MAOP of

the membrane was determined to be the pressure at which it contains 1m3 of biogas (i.e. its full

volume). The safe operating procedure developed to prevent this MAOP occurring is outlined in

Section 9.8.

6.5.4 Insulation

Insulation was added to the system in order to increase temperature of the system and improve thermal

inertia. While situated in the Urrbrae greenhouse, heat was retained by the surrounding atmosphere

which negated the requirement for additional insulation. However, after the system was moved out-

doors on 30 September, insulation became necessary for the anaerobic digestion process to retain

heat overnight. Cheap, readily available materials were considered for insulation, such as newspaper

or polystyrene layering, and bales of hay which could be stacked around the system. Ultimately, a

suitable scrap material became available and was used instead to save costs, and demonstrate that


discarded matter could be practically re-purposed and easily integrated into the system. The scrap

material consisted of two pieces of reflective silver plastic separated by a thick layer of bubble wrap.

A large piece of the material was wrapped around the first digestion tank, and is shown in Figure

6.13. The tank was then wrapped in a layer of black plastic, originally designed for use as a bin liner,

as visible in Figure 6.14. The layer of black plastic allowed the first tank to absorb more heat during

the day, and was an inexpensive and abundant resource. Alternatively, the system could be painted

black or covered by an equivalent black surface.

Figure 6.13: Scrap material used for insulation layer

Figure 6.14: Black plastic layer for heat absorption

6.5.5 Stirrer

A final feature designed and built for the system was a stirring mechanism for the first digestion tank.

The primary function of this device is to agitate any dry scum on the top surface of the effluent,

which has the potential to disrupt the anaerobic digestion process (Rohjy et al., 2013). It also allows


the mixing off different layers, ensuring all effluent is digested equally (Rohjy et al., 2013). There are

associated disadvantages with the addition of this device such as added cost, maintenance, complexity,

and potential gas leakage. For this reason, the inclusion of a stirrer is highly dependent on whether

the technical skills required to build it are available.

Due to delays in construction, the stirrer was not included in the final design for testing. Sufficient

testing would not have been possible if the schedule had been postponed to install the stirrer. However,

the stirrer was still built to investigate the feasibility of constructing an inexpensive, yet effective

component that could increase the biogas yield.

This design was created in accordance with the design criteria outlined in Chapter 5:

Reliability

The design must be gas proof so as not to leak stored biogas. The design should also be simple,

containing minimal moving parts so as to increase the lifetime of the system.

Ease of use

The stirrer should not require strong exertion from the user.

Constructibility and cost

The complexity and number of parts required must be minimised.

Function

The stirrer must effectively mix effluent and break up scum.

The final stirrer design is shown in Figure 6.15, with detailed drawings included in Appendix E. The

critical component of the stirrer was the bearing, which was required to support the weight of the shaft

and paddles, and allow smooth operation as detailed in the criteria. The final bearing system utilised

two plain bearings held in an aluminium housing, which were situated above a neoprene seal. The

reason for this selection over traditional ball or roller bearings was due to its simplicity, which reduced

the cost, and increased the reliability of the stirrer. The plain bearings selected (SKF sintered bronze

C 4048, and F4048-1) were specifically designed for long life applications. The bearings were held in

the housing with a H11 fit, while the shaft was press fit to the bearings with an M6 fit. The neoprene

seal had a 1 mm interference with the shaft. Steel water pipe was used for the shaft, with a length of

1.8 m to allow for mixing at the bottom of the tank. For the mixing paddles, aluminium sheet was

connected to the shaft using L brackets. The width of each paddle was 300 mm, which was a dimension

restricted by the top tank hole diameter of 365 mm. A height of 300 mm was also selected for the

bottom two paddles to ensure the paddle area was relatively small, and did not provide excessive

stirring resistance. A longer paddle was selected for the top paddle to account for variable effluent

levels inside the tank ensuring that surface could always be disrupted. Finally, the layout was chosen


to limit the uneven distribution of weight of the paddles, and resultant forces on the bearing.

Figure 6.15: Final Stirrer Design

Chapter 7

Risk Assessment

This section outlines the risks that can potentially affect the success of the project, along with the

health and safety of the project stakeholders. Risks were identified and assigned a risk level that was

evaluated using likelihood and consequence scales (Section 7.1 & 7.2). If the risk was identified as

a medium or higher level, it was deemed unacceptable. Measures were implemented to prevent or

reduce the effect of unacceptable risks, and are outlined in the risk register in Appendix F.

7.1 Likelihood Scale

A scale with five categories ranging from Rare to Almost Certain was used to rank the likelihood

of occurrence for the risks associated with this project. Alphabetical labels from A to E were also

assigned to these categories to aid in the risk register process. The exact likelihood of each label is

outlined below.

Almost Certain (A): Highly likely to happen, possibly frequently

Likely (B): Will probably happen, but not a persistent issue

Possible (C): Might happen occasionally

Unlikely (D): Not expected to happen, but is a possibility

Rare (E): Very unlikely this will ever happen

(The Univeristy of Adelaide, 2012)

71

CHAPTER 7. RISK ASSESSMENT 72

7.2 Consequence Scale

The consequence scale was be separated into five levels; Extreme (1), Major (2), Moderate (3), Minor

(2), and Insignificant (1). When considering the risks affecting the success of the project, consequence

definitions found in Table 7.1 were followed. Risks concerning safety were evaluated using the conse-

quence scale adopted by the University of Adelaides Risk Management Committee; a summary of the

relevant consequence definitions from this scale is found in table 7.2.

Table 7.1: Consequence scale - risks to project success (The University of Adelaide, 2012)

Consequence Rating Description of Consequence

Extreme (5)The success of the project is compromised to such an extent

that it cannot be completed.

Major (4)The success of the project is permanently compromised to a

significant degree.

Moderate (3)

A significant setback requiring a large amount of work to

overcome. However, only a small amount of, or no, permanent

damage is done to the final project outcomes.

Minor (2) A setback requiring a moderate amount of effort to overcome.

Insignificant (1) A setback requiring small effort to overcome.


Table 7.2: Consequence scale - safety risks (The University of Adelaide, 2012)

Consequence Rating Description of Consequence

Extreme (5)

Serious injury or death, loss of significant number of key staff

impacting on skills, knowledge & expertise, staff industrial

action, student unrest/protest/violence.

Major (4)

Serious injury, dangerous near miss, loss of some key staff

resulting in skills, knowledge& expertise deficits, threat of

industrial action, threat of student protest/activity.

Moderate (3)

Staff injury, lost time or penalty notice due to unsafe act,

plant or equipment, short term loss of skills, knowledge,

expertise, severe staff morale or increase in workforce absentee

rate, student dissatisfaction.

Minor (2)

Health & safety requirements compromised, lost time or

potential for public liability claim, some loss of staff members

with tolerable loss / deficit in skills, dialogue required with

industrial groups or student body.

Insignificant (1)

Incident with or without minor injury, negligible skills or

knowledge loss, dialogue with industrial groups / students

may be required.

7.3 Risk Matrix

The risk matrix (Table 7.3) was used to determine the rating for an identified risk. Table 7.4 outlines

the actions required for each risk rating when considering risks to safety. Risks to project safety were

dealt with using the preventative measures outlined in the risk register.

Table 7.3: Risk matrix (The University of Adelaide, 2012)

Insignificant

(1)

Minor

(2)

Moderate

(3)

Major

(4)

Extreme

(5)

Almost Certain (A) Medium Medium High Extreme Extreme

Likely (B) Low Medium High High Extreme

Possible (C) Low Medium Medium High High

Unlikely (D) Low Low Medium Medium High

Rare (E) Low Low Low Low Medium


Table 7.4: Risk management required (The University of Adelaide, 2012)

Risk Rating Management Action Required

Extreme Risk Immediate attention & response needed; requires a risk assessment

& management plan prepared by relevant senior managers for Vice-

Chancellor; risk oversight by Council or nominated Standing Committee

or Management Committee.

High Risk Risk to be given appropriate attention & demonstrably managed; re-

ported to Vice-Chancellor or other senior Executives/Management Com-

mittees as necessary.

Medium Risk Assess the risk; determine whether current controls are adequate or if

further action or treatment is needed; monitor & review locally, e.g.

through regular business practices or local area meetings.

Low Risk Manage by routine procedures; report to local managers; monitor &

review locally as necessary.

7.4 Heirarchies of Control

The hierarchies of control method - used to determine the course of action after rejecting a risk - is

outlined below. It should be emphasised that in accordance with this method, risks were eliminated

wherever possible.

Hierarchies of control method (Mihelcic & Zimmerman 2010):

1. Eliminate hazard and risk through system (re)design;

2. Reduce risk by substitution with less hazardous methods and materials;

3. Incorporate safety devices;

4. Provide warning systems;

5. Apply administration controls;

6. Provide personal protective equipment (PPE)


7.5 Risk Register

The risk register was used to provide a detailed analysis and review of the risks to the project. It was

split into two major sections: the risks to project success; and the risks to safety. Only ’Low’ rankings

were accepted for the project. The risk register, and an extensive application of this process, can be

found in Appendix F.

Chapter 8

Prototype Construction and Cost

The construction of the prototype system was completed entirely by the members of the project team.

This was done to demonstrate the versatility of the design and its ease of assembly, as listed in the

design criterion in Section 5.3.

8.1 Part Sourcing

With the exception of the gas collection membrane, all parts used in the construction process were

purchased from local suppliers. All items were of standard sizes which are commonly found in most

hardware stores. This complies with the constructability design criterion, to ensure that the design can

be easily built anywhere with access to basic construction materials and skills. Being able to source

all parts from a hardware store or local alternative will make the construction process simpler and

faster. This enables Non-governmental Organisations (NGOs), who typically undertake humanitarian

projects in developing communities, to focus on construction rather than product sourcing.

The gas collection system is a purpose built inflatable membrane which was imported from China. This

UV-stabilised PVC membrane included a heat sealed inlet that could be easily integrated into the gas

piping network. As this part could not be sourced locally it did not comply with the constructability

requirement. However, an effective gas collection system could not be constructed from materials

found in hardware stores without specialised equipment and techniques, which would also not adhere

to the criteria. Therefore as a compromise, a product that was easily integrated into the purchased

parts, effective in its intended purpose and readily available was imported.

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CHAPTER 8. PROTOTYPE CONSTRUCTION AND COST 77

8.2 Construction and Tooling

The construction process was completed using simple tools including drills, spanners, screw drivers,

saws, clamps, and a caulking gun. This was done in order to demonstrate that the system could be

built using inexpensive, readily available tools and facilities. Ideally, for the system to be distributed by

an NGO in a developing country, it must be easy and simple to construct, as advanced manufacturing

facilities and knowledge may not be available. Building the prototype using only basic tools and

technical knowledge demonstrated the ease with which this system can be produced, and highlights

its suitability for use in developing communities.

Construction was performed over a three week period from 2 June to 21 June 2014. It was estimated

to have taken the five project team members five working days to complete. This extended period can

be attributed to delays in material and tool sourcing. Additionally, ensuring the tank lids were sealed

effectively was a difficult, but essential, process causing further delays. The initial sealing mechanism

proved ineffective as air leaks were found when the tanks were filled to test for liquid leaks. An

additional layer of sealant in the form of plastic sheeting was then added to each lid. Subsequent tests

showed this measure was effective in eliminating all gas leaks from the system.

As this was the construction of the first prototype for this design, the time taken would be significantly

longer than any future constructions. If instructions as well as all materials and tools are provided, it

is estimated that the design will take a group of four people a single day to construct.

The stirrer was partly constructed by The University of Adelaide’s mechanical engineering workshop.

The steel shaft was attached to the bearing with an interference fit, which required specialsed man-

ufacturing skills not held by the project group members. The removable paddles were then simply

attached by the project group to complete the design.

8.3 Personal Protective Equipment

To further mitigate the risk of injury during the construction process, personal protective equipment

(PPE) was worn by all members of the construction team. Steel capped footwear was worn by those

involved in lifting heavy objects. Overalls, gloves, and goggles were used by anyone in direct contact

with faecal matter. Safety goggles were worn by the users of power tools and any person in close vicinity

to this activity. This strict use of personal protective equipment combined, with electrical testing of

any power tools used, can be attributed to the absence of personal injury during the construction

process.


8.4 Costing

In accordance with the design criteria, the cost of the prototype construction was kept to a minimum.

The majority of costs were associated with the purchasing of construction materials. However, there

were also additional costs associated with the testing and operation of the project. These costs were

largely met by the project budget, which consisted of core funding provided by University of Adelaide

as well as additional sponsorship.

8.4.1 Secured Sponsorship

This project was allocated funding from the University of Adelaide’s School of Mechanical Engineering

in the form of 200 AUD per group member. This provided a baseline budget of 1,000 AUD. From an

early stage it was estimated that this budget would not meet the financial needs of the project, thus,

it was necessary to seek sponsorship in the form of financial and material contributions.

Potential sponsors were contacted either by phone or email, and supplied with a sponsorship prospectus

(Appendix H). This document outlined the nature of the project, required contributions, and how

sponsors may benefit from their contribution.

Lynair Logistics, an Australian business specialising in international transportation, distribution, and

logistics, kindly donated 300 AUD towards the project budget. Their contribution brought the project

budget to 1,300 AUD.

Caroma, an Australian owned business specialising in bathroom products, generously donated a toilet

system including cistern and pan. Contributions from Caroma had a retail value of 448 AUD.

Subsidised components and expert hardware advice were provided by Barrow and Bench Mitre 10

Malvern. These contributions resulted in savings of more than 500 AUD.

Michael Hatch, a PhD student from the Univeristy of Adelaide, donated four SupelTM gas sample

bags, which cost 16 AUD each. These bags were used to take samples of the gas produced by the

prototype during testing. Mr Hatch also donated his time and the use of a Picarro gas analyser to

measure the methane concentration of these gas samples.

Sponsor contributions have resulted in savings of more than 1,000 AUD, and increased the project

budget by 300 AUD. Without such generous contributions, the project is estimated to have cost

approximately 2,300 AUD. A summary of all sponsor contributions is shown in Table 8.1.


Table 8.1: Sponsorship summary

Sponsor Contribution Project Savings

Lynair Logistics 300 AUD -

Caroma Toilet Cistern and Seat 212.10 AUD

Toilet Pan 236.30 AUD

Barrow and Bench Mitre 10 Malvern 2x 1200L Tanks 400 AUD

Various Components 150 AUD

Michael Hatch 3x Tedlar Gas Sample Bags 48 AUD

8.4.2 Components and Operation Costs

Major prototype costs can be divided into four subsections; tanks, gas membrane, toilet and fittings.

The full retail and project cost of each subsection is shown in Table 8.2 with detailed summary of

all purchases can be seen in Appendix G. All components were acquired from local stores and online

retailers.

Table 8.2: Prototype cost summary

Subsystem Retail Cost (AUD) Project Cost (AUD)

Tanks 800 400

Gas Membrane 175 175

Gas and Plumbing Fittings 425 258

Toilet 445 0

Total 1845 833

As shown in Table 8.2, discounts received for the project reduced the cost of the prototype by approx-

imately 45%. Although the cost of materials will vary depending on the location of implementation,

discounts similar to those received by this project are possible. Therefore the cost of 833 AUD can be

used as a reasonable estimate for the total cost of the system.

Operation and testing costs contributed approximately 100 AUD to the total cost of the project.

These purchases included the purchase of PPE, buckets, funnels, drums and litmus paper for pH

measurements. These costs may not be required if the system were to be implemented in a developing

nation, and so were not included in the system cost estimate.

The total cost of the stirrer assembly was 102 AUD. Despite earlier estimates that the stirrer would

be an expensive design addition, this demonstrated that it can be constructed for relatively low cost.

Therefore, it can be concluded that if some technical skills and knowledge are available during the


implementation of the system, a stirrer is an effective, low cost solution to increasing biogas yield.

Taking all expenses into account the project reached a total cost of 1324.61 AUD, exceeding the budget

by by 24.61 AUD. These extra expenses were accommodated by the project team.

8.4.3 Recycled Design Alternatives

Additional cost reductions can be achieved by the substitution of components with recycled or scrap

materials, examples of which are provided in Table 8.3. All components for the construction of

the prototype were brand new; however, substantial savings could have been achieved through the

integration of locally available alternative components.

Table 8.3: Recycled component alternatives

Component Recycled Alternatives

TanksA range of different tanks, including septic and water tanks, are

suitable

Neoprene Sealing

Any available rubber is suitable for sealing purposes, though it may

degrade from hydrocarbon exposure and require replacing. This rubber

could be recycled from a range of sources such as floor skirting, or the

inner tube of a bicycle or car tire

Bioballs

Crushed bricks, scrap plastic, or any non-reactive, non-buoyant object

can be used as substitutions for bioballs to increase the surface area

within the digestion tanks

PipingIf UV treated PVC is not available, normal PVC can be used with

shading. Ceramic, steel, or brass pipes are also suitable

Flexible

ConnectionAny flexible, sealed piping can be used

Insulation

Almost any material that covers the digestion tanks is suitable. For

example; hay, polystyrene, bubble wrap, newspaper. Alternatively the

digestion tanks could be buried underground to trap heat.


8.4.4 Labour

Individual hours spent working on the project by each group member were recorded in order to

estimate costs of the project if it had been undertaken by paid professionals. A log of these hours is

shown in Appendix I. Labour costs are calculated based on an hourly rate for an average graduate

mechanical engineer annual salary of 55,000 AUD (Open Universities Australia, 2014). Approximate

labour costs of the project reached 69,725 AUD for 20 weeks of work. This equates to 13,945 AUD

per group member.

Chapter 9

Testing and Operation Procedures

After construction was completed, testing was required to prove that the system could function as

expected. Testing was run from 12 September to 21 October. The results compiled from testing

provided a means of assessing the effectiveness of the design in achieving the project goals outlined

in Chapter 4. It was originally planned that a minimum testing period of three months was required

to collect enough data for robust analysis, however delays in construction significantly reduced this

testing time.

9.1 System Location

Urrbrae Agricultural High School (UAHS) were willing to house the biodigester prototype on their

campus. Originally, the system was placed inside a greenhouse to provide extra warmth during the

colder period of testing. The system was moved outdoors near the UAHS piggery on the 30 September,

after approximately three weeks of testing due to practical and safety considerations. The outcomes

of moving the system outdoor are discussed in Chapter 10. Practical and safety considerations were

the main reasons for moving the system, along with demonstrating its portability.

The doors of the greenhouse were too small to remove the prototype while upright, hence, tilting the

individual tanks to remove them from the greenhouse was required. If the tanks were full, they would

be difficult to tilt and move safely. It was impractical to empty the entire 2000 L of effluent from the

system at the end of the testing period, as the waste had to be disposed of near the UAHS piggery,

approximately 200 m from the greenhouse. Therefore, the system was moved before it was completely

filled with waste, so that it could easily be emptied after the testing period.

Although the system was routinely checked for leaks, there remained the risk of failing to identify

possible points where gas could escape. Thus, another important consideration was public safety. As

82

CHAPTER 9. TESTING AND OPERATION PROCEDURES 83

discussed in Section 10.2, the gas composition was increasing in methane concentration, indicating

that a flammable biogas mixture could begun to develop. If this gas were to leak into the greenhouse,

it could potentially concentrate in the roof cavities and create an explosive atmosphere. Students

and teachers frequently use the greenhouse for class experiments so this risk was deemed unaccept-

able. Moving the system outdoors after the three week period ensured operation in a well ventilated

environment, minimising the risk of fire and explosion.

9.2 Prototype Assessment

Prior to introducing feedstock to the biodigester, all pipes and connections were checked for leaks.

By ensuring both biogas and feedstock leaks were minimised, the risk of fire, explosion and expo-

sure to pathogens was significantly reduced. The system was tested for both liquid and gas leaks

simultaneously using the following procedure:

• All valves were opened, excluding the two outlet valves at the bottom of the tanks.

• The system was then filled with approximately 1000 L of water, and all fittings checked for liquid

leaks.

– Because the valves connecting the two tanks were opened, each tank was approximately

half-full

– As both tanks were completely sealed, the addition of 1000 L of water to the system

displaced 1000 L of air into the gas pipeline and membrane

• Soapy water was lathered over all gas connections to detect any escaping air from the system.

– This would identify any points that would allow leak biogas

• Water was left in the tanks for a period of five days to ensure no leaks would develop over time

9.3 Feedstock Selection

Although the biodigester system was designed to produce biogas using human waste as the feedstock,

it was decided that the prototype would be tested using pig waste instead. Two major factors were

behind this decision; accessibility to feedstock and similarity to human waste.

It was too difficult to source a reliable supply of human waste to use as a feedstock for testing. Along

with the obvious biological hazard presented by handling human waste, it was impractical to collect

human waste and feed it into the system on a regular basis. The system was not completed to a stage


that would allow privacy, therefore waste could not be collected through its implementation as a toilet

on the UAHS grounds.

As the biodigester was located on the UAHS campus, pig waste could easily be collected from the

piggery on the school’s farm and transported to the system within the greenhouse. Based on the

information presented in Table 3.2, pig waste was a suitable substitute for human waste. Per unit

mass, it produces a similar volume of biogas to human waste when compared to other animals. Al-

though chicken waste is also a suitable substitute in terms of biogas production per unit mass, pig

waste was much easier to collect from the UAHS farm. Based on these practical and scientific consid-

erations, it was decided that pig waste sourced from the UAHS piggery would be used as the testing

feedstock.

9.4 System Start-up

During the construction phase, four sealed 76L drums were filled with pig waste from the UAHS

piggery on 28 August. This was done to begin to digestion process independently of the system.

Anaerobic digestion typically takes between 40 to 45 days to occur (Abbasi et al., 2012). To ensure

the project objective of producing a working biodigester was achieved, it was deemed necessary to

begin the digestion process early so that biogas yields could be optimised within the testing timeframe.

Once the system was constructed and the necessary safety tests conducted, the waste from these drums

was added to the system.

There are risks associated with the start-up of a biodigester system, paramount of which are the

dangers of fire or explosion. Methane-air mixtures become explosive with a lower flammability limit

of 5% concentration of methane in air (Glassman and Yetter, 2008). To reduce the risk of explosion,

the gas mixture from the system was vented to the atmosphere after each sample was taken. Samples

were routinely analysed to monitor methane concentration to identify when concentrations began to

approach the lower flammability limit.

9.5 Continuous Process Digester

Based on equations presented in Section 6.2, the amount of feedstock entering a toilet system being

shared by 14 people was calculated:


Waste Volume (L) = 4.48×U (9.5.1)

= 4.48× 14

= 62.72 L

Equation 9.5.1 shows that approximately 63 L of solid and liquid waste will be added daily to the sys-

tem by 14 users. It was impractical for members of the project team to be present at UAHS every day

to load the system with waste, based on university timetable restrictions and school opening hours.

It was therefore decided that 220 L of total feedstock would be added twice per week. This operat-

ing procedure aimed to produce steady state gas production, which was expected after the required

retention time for mesophilic digestion of approximately 30 days (Suryawanshi et al., 2013).

9.6 Operating Conditions

The volume and composition of gas produced via anaerobic digestion is dependent on physical factors

such as temperature, pH and the presence of volatile solids, volatile fatty acids, molecular hydrogen

and ammonia-nitrogen within the system (Labatut and Gooch, 2012). Many of these factors are

difficult to measure and control, especially when considering a system to be implemented in developing

communities with limited access to scientific apparatus. Both temperature and pH are simple to

measure and adjust if required, therefore they were monitored throughout the testing period. For an

outline of results obtained, and a discussion of their significance, refer to Chapter 10.

The temperature inside the digester should be maintained between 35◦C and 45◦C to optimise

mesophilic anaerobic digestion (Labatut and Gooch, 2012). To ensure this mesophillic range, the

temperature of the anaerobic digestion tank at the inlet and base was measured twice weekly. Tem-

peratures outside this range could decrease the rate of gas production, with extreme fluctuations

resulting in the death of anaerobic bacteria.

A system pH of neutral or slightly alkaline (pH 7 to 7.5) presents ideal conditions for healthy anaerobic

bacteria function. The pH of and effluent samples was measured twice weekly to monitor system health.

The system pH was found to follow the typical trend of an anaerobic digestion process, as discussed

in Section 10.3. A discussion of simple methods of adjusting system pH to ensure effective digestion

is presented in Section 10.3.1.

Any gas leaks present in the prototype during testing would reduce biogas yields and increase the risk

of fire. To mitigate this risk, the entire prototype was checked weekly for leaks by applying a water

and detergent solution over the surface of all gas carrying components. If bubbles were spotted on the


surface, the leak could be identified and appropriate repair measures taken. Typical repairs involved

the addition extra silicon sealant over the leak, the application of high-strength weatherproof tape,

and replacement of gas-proof plumbing tape. These repair schemes were developed with consideration

to materials available in countries that would benefit most from the implementation of a biodigester

toilet.

9.7 Biogas Collection and Results

Biogas was collected in a flexible membrane located at ground level beside the digestion tanks. As

outlined in Section 6.5, the membrane was fitted in such a way that it could be isolated from the rest

of the system and gas samples extracted with ease. Methane concentration of the gas captured was

sampled over the entire testing period.

To test concentration, SupelTM Inert gas sampling bags were used to collect biogas samples twice per

week. These sample bags were suitable for testing as they provided a low risk of sample contamination

and other desirable physical properties as outlined in Appendix J. A biogas sample contained within

a bag can be seen in Figure 9.1. Biogas samples were analysed using a Picarro G2201-i Analyzer,

which “precisely measures CO2, H2O and CH4 concentration” (Picarro, 2014). The sampling bags

were flushed with hydrogen gas to enable re-use without contaminating new samples. The gas sam-

ple analysis and a discussion of composition change over the testing period is presented in Section

10.2.

The Picarro G2201-i Analyser is designed to simultaneously measure the concentrations of methane

and carbon dioxide every 5 seconds in a sample of air and record the readings using Picarro software.

A data sheet containing detailed specifications of the analyser can be found in Appendix K. The high

range mode of the analyser accurately measures methane concentrations from 1.8 ppm to 1000 ppm.

The same mode is able to measure carbon dioxide concentrations up to 4000 ppm. The concentrations

of methane and carbon dioxide contained within biogas samples taken from the system greatly exceeded

these values and this created some inaccuracy in results, discussed further in Section 10.2.


Figure 9.1: Tedlar bag filled with gas sample

9.8 Safe Operating Procedure

A safe operating procedure (SOP) was developed for the testing phase of the system. The SOP was a

two-tier procedure, designed to prevent over-pressure situations and also to ensure that those testing

the system were not exposed to harmful pathogens.

9.8.1 Preventing over-pressure situations

It was assumed that as soon as the entire volume of the collection membrane (1 m3) had been filled

with gas, it was at risk of bursting. This was the worse case scenario for the MAOP of the collection

membrane, as discussed in Section 6.5.3. To ensure the membrane would never completley fill with gas,

it was vented every Monday and Thursday during the testing period, coinciding with the collection of

gas samples. This also ensured that each sample would contain gas produced since the previous test,

thereby monitoring the biogas composition change over the testing period.

It is important to note that the MAOP of the biogas collection membrane is a ciritcal factor in

determining the maximum internal gas pressure to be placed on the system. As this MAOP was not

known there was potential for it to be much less than the MAOP of the gas pipeline and fittings

(calculated in Section 6.5.1). Therefore the routine emptying procedure was required.

9.8.2 Handling Feedstock

As outlined in Section 2.1.2, excreta can contain a number of harmful pathogens. Although human

waste was not used in testing, any animal waste is still a potential source of illness if handled incorrectly.


To ensure persons involved with loading pig waste into the system would not come into direct contact

with the excreta, the use of personal protective equipment (PPE) was made mandatory when any

feedstock was being added or removed. This personal protective equipment consisted of:

• Gloves

• Safety glasses

• Disposable overalls

• Face mask

Although the use of PPE is last on the hierarchies of control list (presented in Section 7.4), during

the first three weeks of testing it was the most appropriate for preventing exposure to pathogens in

the feedstock. This was because the system was located inside the UAHS greenhouse, approximately

200 m away from the piggery. This distance made it impossible to pump waste directly from the pig

waste reservoir into the system, so it had to be transported in 76 L drums to the greenhouse and

loaded manually into the system using buckets. As discussed in Section 9.6, the system was moved

closer to the piggery after the first three weeks of testing. This enabled waste to be pumped directly

from the reservoir into the system inlet, and reduced the risk of exposure to pathogens even more.

The use of PPE was still required when filling the system using the pump.

Chapter 10

Results and Discussion

As outlined in Chapter 9, a number of parameters were recorded during testing to provide a better

understanding of how the anaerobic digestion process progressed during operation. Methane compo-

sition, various temperatures, and pH were measured. The recorded data is presented in this chapter,

along with a discussion of the significance of each parameter. Also discussed is the level to which the

project objectives were achieved.

10.1 Gas Analysis

Samples of biogas were collected in SupelTM Inert gas sampling bags which feature a push-lock valve

mechanism. These samples were collected bi-weekly over the five week testing period and measured

using a Picarro G2201-i Analyser. Numerical results obtained from the biogas sample analysis can be

found in Appendix L.

The Picarro 2201-i analyser was a useful tool in assessing methane concentration of the biogas. How-

ever, as the analyser is only designed to measure methane concentrations of up to 1,000ppm, it can

not be relied upon to deliver scientifically accurate results. While performing analysis, the Picarro

2201-i struggled to provide measurements of the methane concentration at the frequency specified

by Picarro, However, the results obtained were found to be consistent with expected methane con-

centration. Thus, these results can be used as an indication of the general trend in the methane

concentration over the testing period but cannot be relied on for numerical accuracy.

Similarly, the anaylser is only designed to measure carbon dioxide concentrations up to 4,000ppm.

Values of carbon dioxide concentration delivered from the Picarro 2201-i were too infrequent and

inconsistent to provide any reliable measurements. The analyser stopped responding when carbon

dioxide measurements exceeded approximately 45,000ppm and thus the measurements obtained are

89

CHAPTER 10. RESULTS AND DISCUSSION 90

not presented here as results. From this analysis it can only be concluded that the concentration

exceeded 45,000ppm in each sample.

10.2 Methane Concentration

Figure 10.1 shows the change in methane concentration over time. It is clear that methane concentra-

tion increased at an increasing rate during the testing period. The drop in concentration shown for

the date of 3 October can be attributed to the disassembly and transportation of the prototype in the

days before this sample was taken. This process required various valves on the tanks to be opened, for

reasons discussed in Section 10.5. Thus, oxygen was re-introduced to the system which both diluted

the next scheduled sample with air, and hindered the digestion process.

0

5000

10000

15000

20000

25000

Met

han

e C

on

cen

trat

ion

(p

pm

)

Date (DD/MM)

Figure 10.1: Change in methane concentration over testing period

The lower flammability limit of methane in air is 50000 ppm (Glassman and Yetter, 2008). Biogas

will not burn until the concentration of methane is above this flammability limit. The last results

analysed showed a methane concentration of 23,349 ppm; a significantly larger value than the initial

reading of 259 ppm, four weeks prior. These results demonstrate that anaerobic digestion occurred

within the system, and the process was effective in producing methane. As will be discussed in Section

10.3, pH measurements indicated that anaerobic digestion had not reached the methanogenesis stage,

in which the majority of methane production occurs. Given more time, the gas is predicted to become

flammable as the anaerobic digestion process progresses.


Comparisons between the methane concentration data collected for the project, and experimental

data obtained by Sulistyo et al. (2012) for the anaerobic digestion of three different substrates (S1, S2

and S3 in Figure 10.2), demonstrate similar trends in methane generation. Note, the three substrates

tested by Sulistyo et al. (2012) were different mixtures of cow manure and plant material. Substrate

1 (S1) had no cow manure in it, S2 was 90% cow manure, and S3 was 36.4% cow manure. While

the feedstocks used by Sulistyo et al. (2012) are different to the pig manure used in this project,

the change in methane concentration between the two experiments follow similar upwards trends.

This is significant, as it confirms that the anaerobic digestion process occurred within the biodigester

toilet.

Figure 10.2: Change in methane concentration for different substrates (Sulistyo et al., 2012)

A flame test was conducted in the final week of testing to investigate the flammability of the gas

produced by the system. Two gas samples were collected in small inflatable membranes. An identical

membrane was filled with air to use as a control sample. All samples were then removed from the

vicinity of the biodigester, and tested by exposure to a small flame. None of the samples ignited,

indicating that the gas produced by the biodigester was not flammable. This practical result reinforces

what was concluded from methane concentration measurements and combustion theory.

10.3 pH

As discussed in Section 3.3.3, pH has a strong correlation with the health of an anaerobic digestion

system. Hence, monitoring feedstock pH throughout the entire testing process was important to ensure

the digestion process was progressing as expected. Tracking pH also enabled the observation of the

four stages of anaerobic digestion, each of which has a characteristic pH range. To monitor pH, litmus

paper testing strips were used. These strips are inexpensive, available from local and online retailers,


and negate the need for complicated testing methods, demonstrating how system pH can be monitored

for a small cost in a developing community.

The pH of the first digestion tank was monitored throughout the testing period and the pH of the

second tank was monitored once effluent was transferred to it. For each test a sample of effluent had

been taken from outlets at the base of each tank which are the only points of access to the feedstock

after it enters the system. These effluent samples were then tested with the litmus paper. This release

of effluent increased the risk of pathogen exposure, making the use of PPE necessary. A graph showing

the change in pH throughout the testing phase is shown in Figure 10.3, with numerical result found

in Appendix L.

4.5

5

5.5

6

6.5

7

7.5

pH

Date (DD/MM)

Digestion Tank Sedimentation Tank

Figure 10.3: Change in system pH over testing period

For the digestion process to begin, feedstock pH must be between 6.8 and 7.5 (Environmental Protec-

tion Agency, 2012). Initially, the pH in the first digestion was neutral (pH = 7) and began to decrease

over time to a value of 6. This result was expected, as the second and third phases of anaerobic

digestion, acidogenesis and acetogenesis, are characterised by the production of fatty acids and acetic

acids, respectively. As discussed in Section 3.3.3, a reduction of system pH to as low as 5.5 can be

expected during acetogenesis.

As fresh waste entered the system at the bottom of the first tank, older waste was pushed upwards.

The transfer point between the two digestion tanks was 860mm from the base of the tanks, ensuring

older waste above this level would be transferred to the second tank. Figure 10.3 shows an increase of

pH level from 5 to 6.5 in the second tank. This was expected, as the second tank contained older waste


that was transitioning into the methanogenesis phase, the final stage of anaerobic digestion. Ammonia

is produced during the methanogenesis phase, causing pH to increase (Wang et al., 2007).

The pH measurements in both tanks followed the trends expected for anaerobic digestion. When

considering these pH measurements in combination with the methane concentration measurements, it

is apparent that the anaerobic digestion process was progressing.

10.3.1 Controlling pH

As system health has a strong dependence on feedstock pH (Karki and Dixit, 1984), it is important

to have the ability to adjust the system pH if required. If the system pH had become unsuitable for

anaerobic digestion at any stage throughout the testing period, it would have been possible to adjust

this using off-the-shelf products designed to adjust the pH of various mixtures.

As the design is intended for use in developing communities, which may not have access a wide variety

of chemicals, it is important to highlight a number of ways to alter pH using readily available materials.

If pH in the system is required to be lowered, a number of simple materials and techniques can be

used to achieve this. Food waste has a tendency to decompose quickly, which will decrease the pH of

the digester (Environmental Protection Agency, 2012). If testing shows an unsuitably high pH, food

waste from kitchens can be added to the digester to lower it. Adding lemons, oranges, and other fruit

containing citric acid is another way method of increasing acidity. Raising system pH is more difficult;

however, sodium bicarbonate (baking soda) is a commonly available product that can be added to

the system to increase alkalinity. It is commonly used to increase the pH of swimming pools, and can

simply be added to the inlet of the biodigester, and flushed with water.

10.4 Temperatures

As anaerobic digestion is highly sensitive to temperature, it was necessary to monitor various tem-

peratures throughout the testing period. Measurements were taken using a long-probed electronic

thermometer during the hours of 9am to 3pm. Temperature measurements were taken for the inlet of

the first digestion tank, for ambient conditions, and for effluent samples sourced from the base of each

digestion tank. In order to assess the effectiveness of the greenhouse and insulation strategies, mea-

sured results were compared with temperature readings from nearby weather stations. Using resources

from the Bureau of Meteorology (BOM), temperature readings from 9am and 3pm were averaged from

weather stations located in Kent Town and the Adelaide Airport, the closest stations to UAHS with

similar altitudes. This comparison is shown in Figure 10.4 with numerical values found in Appendix

L.


12

15

18

21

24

27

30

33

36

39

20/09 22/09 24/09 26/09 28/09 30/09 02/10 04/10 06/10 08/10 10/10 12/10 14/10 16/10 18/10 20/10 22/10

Tem

per

atu

re (

°C)

Date (DD/MM)

Inlet Effluent BOM Average Testing Site Ambient

Figure 10.4: Temperature measurements compared to BOM readings

The system was removed from the greenhouse on 30 September, which can be seen as a drop in all

measured temperatures in Figure 10.4. To combat this fall in temperature, an insulating material was

attached to the first digestion tank on 9 October. The addition of this material corresponded to a

stabilisation of the inlet temperature, and an increase of effluent temperature, suggesting it was an

effective method of insulation.

It can be seen that despite BOM recorded temperatures following a cyclic curve, the inlet and effluent

temperatures display a more steady temperature gradient. This can be attributed to the effectiveness

of the insulation provided initially by the greenhouse and later, the insulating material.

As expected, inlet temperatures were shown to be consistently higher than effluent temperatures,

usually with a margin of up to 5◦C. Inlet temperature recordings appear to follow the same general

trend as the ambient temperature. Ideally, inlet temperatures will be slightly higher than ambient

temperatures to demonstrate the heat being retained in the system for anaerobic digestion. However,

as the majority of readings were taken in the early hours of the morning, it may be reasonably deduced

that the system, due to higher thermal inertia, had been absorbing heat from the surrounding air at

a much slower rate.

Effluent temperature readings show that the system was operating at a lower than optimal temperature

for mesophillic digestion (30 to 38◦C). However, as previously mentioned, anaerobic digestion did occur

but the rate of digestion was likely retarded by low temperatures.


10.5 Portability Demonstration

Portability was demonstrated by relocating the system from the Urrbrae greenhouse to the Urrbrae

piggery. The reasons for relocation of the system are discussed in Section 9.1. As the tanks were

situated on 2 pallets, the use of a forklift and a pallet jack enabled the system to be easily transported.

Placing two ball valves between the tanks enabled them to be isolated, and transported individually.

Biogas collected in the gas membrane was easily separated from the biodigester and moved to a

different location by hand.

The doors of the Urrbrae greenhouse were too small to fit the tanks through upright so they had to

be partially emptied and tilted. If this had not been the case, the protoype could have been moved

with less disruption to the digestion process and, consequently, methane concentration would not have

been affected.

Proving that the design is portable has significance when considering the implementation of the sys-

tem in a developing community. The prototype was constructed from materials easily sourced from

hardware stores, however these resources may not be readily available in every community. Being

portable, the system could be constructed at a location with the available resources by an NGO or

similar organisation, and then transported to where it is required. Being able to isolate each tank

while full of feedstock also makes it possible to relocate the system after it has begun operation.

10.6 Completion of Objectives

A number of project objectives were outlined in Section 4.2. The extent to which these objectives

have been met will be discussed.

1. Design and build a portable toilet that meets the definition of a Shared Sanitation

Facility, as outlined by the WHO/UNICEF Joint Monitoring Program (JMP) for Water

Supply and Sanitation.

The system was checked for liquid leaks using fresh water before feedstock was added during the testing

phase. No leaks were identified from this initial test, and none developed during the entire testing

period. Once the feedstock entered the digester, it was completely separated from human contact.

Thus, the system satisfied the WHO definition of an improved sanitation facility, as it “...hygienically

separates human excreta from human contact” (WHO and UNICEF, 2014a). Calculations presented

in Section 6.2 showed that the final design is capable of effectively digesting the waste of 14 daily users.

The WHO defines shared sanitation facilities as “...sanitation facilities of an otherwise acceptable type,

that are shared between two or more households.” (WHO and UNICEF, 2014b). Current census data


from India and China indicates that the average number of permanent residents per household in

rural areas is 5.4 and 3.88, respectively (National Bureau of Statistics of China, 2013; The Registrar

General & Census Commissioner, 2011). Using these statistics as an estimate for average household

size in the developing world, and noting that the final design is an acceptable facility, the prototype

can be classified as a shared sanitation facility.

2. Include a functioning biodigester component in the design that is capable of harnessing

the human waste collected in order to produce biogas.

The success of this goal was originally based on the biogas production rate by volumetric measurement

(litres of biogas produced per kilogram of feedstock). As there is not a fixed definition for the chemical

composition of biogas, this goal is difficult to quantify using the originally proposed method. As stated

in the discussion in Sections 10.2 and 10.3, methane was being produced within the system, and pH

measurements indicated that the acidogenesis and acetogenesis phases of anaerobic digestion were

taking place. These results indicate that the system was functioning as an anaerobic biodigester.

3. Integrate the toilet with the biodigester to create a portable biodigester toilet

unit.

The system inlet was constructed from 100mm diameter sewerage grade PVC pipe, to allow for the

integration of standard 100mm toilet outlets. While the prototype was located within the UAHS

greenhouse, there was not enough overhead room to mount the toilet on top of the first tank. After

relocating the system outside, it was assessed that the available project budget would not allow for

the construction of a safe supporting structure that could hold the weight of the toilet and user. The

toilet was not physically installed on the prototype, however the design enables the integration of any

toilet with a standard 100mm outlet.

As discussed in Section 10.5, the portability of the design was demonstrated when the prototype

was relocated during the testing period. The methane concentration dropped during this relocation

process due to air entering the system, however this would not usually be the case if the system could

remain upright throughout the moving procedure. It can therefore be concluded that the system is a

portable biodigester toilet.

4. Ensure the design is acceptable for implementation and use in Australia by ensuring

it meets relevant Australian standards.

Australian standards relevant to small-scale biodigesters were identified based on the Code of Practice

for on-farm biogas production and use on piggeries (Davidson et al., 2013). Although a number of

standards were identified, only those relating specifically to the materials and technology used in the

final design were adhered to.


AS 4130 and AS 4645 were used to calculate the MAOP of the gas piping, as these standards specifically

relate to polyethylene piping in pressure applications, and gas networks. Other standards originally

identified as relevant in Table 5.1 did not relate to the final design. These standards concerned the

operation of biogas appliances such as generators and flares, or outlined principles relating to the

conveyance of fuel gases in metal pipelines.

5. Demonstrate a viable use for the gas generated by the biodigester.

Standard gas appliances are not equipped to function effectively with low pressure gas, making quan-

tification of this goal difficult. Specially modified stoves or lamps were not available so a simple flame

test was conducted. Success of the flame test would prove that the gas generated by the system could

be used for cooking, heating or lighting. Unfortunately this test proved the gas was not combustible

by the completion of testing. As discussed in Section 10.2, it is expected that the gas will reach

a flammable, and hence useful composition as the anaerobic digestion process progresses into the

methanogenesis phase. Delays in prototype construction restricted the time available for testing, and

results suggest that the methanogenesis phase was not reached during the testing phase.

Chapter 11

Future Work

The extension objectives outlined in Section 4.3 were not completed due to financial restrictions and

time constraints. These extension objectives form the foundation of future work that may be performed

to improve the design.

11.1 Extension Goals

As the prototype system was only operated in a scientific testing capacity, a suitable cubicle to house

the toilet for privacy was not constructed. This would have also exceeded the project budget, and

delays in prototype construction left little time for the completion of this extension objective. To

enable the implementation of the biodigester toilet in developing communities, the construction of the

cubicle is essential.

Time restrictions prevented extensive research being performed on post-treatment methods for the

liquid and solid effluent from the system. To design a satisfactory system, a significant amount of

time should be devoted to its development. This would ensure the treated liquid and solid effluent

would be safe for use as a fertiliser and would not pose a risk to persons who comes in contact with

it.

11.2 Design Improvements

A more appropriate gas collection system must be developed to simplify the use of biogas by the end

users. The current inflatable membrane system is inexpensive and effective in capturing the biogas,

however it can be easily damaged and would require a protecting structure if implemented in any

practical environment. It is recommended that a floating drum system be employed as an improved

98

CHAPTER 11. FUTURE WORK 99

gas collection system as it is able to provide a constant gas pressure, and can be made from materials

less prone to puncture. Difficulties resulting from gas backflow and high pressures may be present in

this type of system and would need to be overcome.

Currently the gas collection system must be removed from the entire system for the gas to be sampled

for combustibility. To simplify the practical use of the biogas for end users, the gas collection system

must incorporate an output hose as well as the input from the digestion tanks. This output should

incorporate fittings to enable the connection of a range of devices such as gas cook stoves, lights or

heaters to the gas membrane. A flame arrester must also be incorporated to reduce the risk of fire

and explosion.

Chapter 12

Conclusion

Research revealed that health implications resulting from poor sanitation practices, and the indoor

use of solid fuels kill over 4 million people every year. Billions of people are affected by these problems,

often in conjunction with crippling poverty conditions. Based on these problems, and the fact that

they are both primarily concentrated in similar developing regions, a project aim was identified to

address both these issues

After investigating various wastewater treatment technologies, anaerobic digestion was found to be

the ideal solution to treat waste, and provide a clean burning alternative to solid fuels. Integrating

an anaerobic digestion system, or ‘biodigester’ with a toilet, creates a system that separates human

excreta from human contact, whilst providing an alternative energy to solid fuels in the form of

biogas.

The University of Adelaide Honours Project 777 team explored one concept of a biodigester toilet

system in 2009. This was a two tank design that used an inflatable membrane for gas collection. The

advantages of this system were portability, and the ability to clarify effluent through a settling process

in the second tank, in preparation for the post-digestion filtering. There were a number of significant

improvements that could be made to Project 777, which were subsequently integrated in the concept

design phase of the current project. These improvements included removing all gas leaks, eliminating

gas back flow problems, allowing for a longer hydraulic retention time, and operating the system in

more suitable conditions. In this project, the number of people able to use the system was calculated

based on the tanks available, average amounts of excreta produced per user each day, and the retention

time required for anaerobic digestion be effective. Relevant Australian Standards were identified to

ensure the design met all safety, environmental protection, and material selection criteria.

Based on required components and resources, costs were projected within the project budget. One of

the project objectives was to assemble the system entirely from readily available parts, which would

100

CHAPTER 12. CONCLUSION 101

increase the feasibility of the system for a larger demographic of people. Additionally, the integration

of readily available resources, and limitations to design technicality, meant that there was scope for the

design to be shared with users with less technical experience. A sponsorship prospectus was created

and sent to potential sponsors in order to help finance the project. Lynair Logistics provided 300 AUD

in sponsorship, increasing the project budget to 1,300 AUD. Sponsorship was acquired from Barrow

and Bench Mitre 10 Malvern, who supplied two polyethylene water tanks, and additional components

at discounted prices. Caroma made contributions of a toilet bowl and cistern at no cost. Michael

Hatch from the University of Adelaide, provided various contributions to the project and played a key

role in the testing process. The total cost of the project including all current confirmed sponsorship

came to 1,208 AUD, which was partially financed by The University of Adelaide to a value of 1,000

AUD.

The first step in the build and operation of the project was securing a location, which was a sensitive

issue due to the potential risks and hazards relevant to the project. An agreement with Urrbrae

Agricultural High School was established, which was mutually beneficial due to the initialisation of

their own biogas program, running concurrently. The biodigester was situated in a greenhouse to best

simulate the tropical conditions found in the majority of developing regions around the world. Pig

waste was used for the feedstock, as it was easily available from Urrbrae’s farm, and did not pose

the health risks associated with exposure to human waste. The daily amount of feedstock and water

supplied to the system was chosen to be 63 L of solid and liquid waste, based on the average daily

human waste production and flushing water per use. This equated to a total of 220 L of waste added

daily. Operation and testing procedures were performed for 7 weeks and the biogas output collected

twice a week. Biogas samples were collected and analysed, showing a significant transition of carbon

dioxide and methane concentration to an increasingly flammable substance, which has been verified

through flame tests.

The core objectives for this project, as outlined in the Scope, defined the assessment criteria by which

the success of the end product was assessed. The first objective stated that the project would in-

volve the design and construction of a portable toilet that qualifies as a Shared Sanitation Facility

according to the WHO/UNICEF Joint Monitoring Program for Water Supply and Sanitation. This

objective was completed successfully, as the addition of a toilet ensured hygienic separation of human

excreta from human contact for the user. For the second objective to be achieved, a functioning

biodigester component would have to be designed to collect the biogas produced from the harnessed

waste. The successful completion of this objective was achieved through the design and construc-

tion of a biodigester prototype with an effective gas collection system. Testing and analysis of the

captured biogas suggested that an increasing methane concentration level was indicative of the gas

approaching flammability. Objective 3 was successfully completed as the inlet for the biodigester

CHAPTER 12. CONCLUSION 102

prototype allowed for a connection to a standard toilet. Designing the system for ease of assembly

and disassembly, allowed for easy relocation during the testing phase to demonstrate portability. The

fourth objective specified that, for the design to be implemented and used, it had to first abide by any

relevant Australian Standards. This was achieved by following relevant standards during the design

and construction stages of the process. The final core objective was to demonstrate a viable use of

the captured biogas. Although initial flame tests showed that gas was incombustible, it is expected

that the methane concentration will increase due to the progression of anaerobic digestion, and the

gas will likely reach a flammable state, given enough time.

Poor sanitation, and the household burning of solid fuels are issues that adversely affect the lives of

billions of people worldwide. These problems, while independent, are concentrated in similar regions,

and thus affect similar populations. In order to effectively address these problems, the overall aim

of this project was defined with the need: “To develop a single appropriate technology that may

be implemented in developing communities in order to alleviate the dangers associated with unsafe

sanitation practices and the household burning of solid fuels.” Overall, the design and build of a

biodigester toilet is considered to be successful as each core objective has been met. With further

research, and an increased scope for testing and implementation, this project has the potential to

positively affect the lives of billions of people worldwide.

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Appendix A

Project Timeline

Table A.1: Project Review Gates

Review Gate Task completed up to review gateTask to commence

after review gate

Review Gate 1:

Research

All group members have a full

understanding of the workings of a

biodigesters as well as the design

requirements of the system.

Design of system.

Review Gate 2:

Whole System

Design

All engineering drawings have been

completed for each subsystem and the

system assembly.

Construction of the

prototype.

Review Gate 3:

Prototype

Prototype is constructed and has received

the necessary professional approval.Testing of system.

Review Gate 4:

Testing

Sufficient data is collected to provide a

reliable conclusion for the performance of

the design.

Completion of

deliverables.

109

APPENDIX A. PROJECT TIMELINE 110

Table A.2: Major Milestones, Review Gates and Due Dates

Item Due Date

Review Gate 1 03/03

Project Charter 01/04

Progress Report 1 2/05

Review Gate 2 20/05


Preliminary Report 06/06

Project Management Plan 06/06

Review Gate 3 06/06


Seminar Abstract 29/08


Testing completion 19/10

Poster 21/10

Final Report 24/10

Project Completion Report 07/11

APPENDIX

A.PROJECT

TIM

ELIN

E111

Figure A.1: Project Gantt Chart

APPENDIX

A.PROJECT

TIM

ELIN

E112

Figure A.2: Project Gantt Chart continued

APPENDIX

A.PROJECT

TIM

ELIN

E113

Figure A.3: Project Gantt Chart continued

Appendix B

CAD Drawings

A Computer Aided Design (CAD) model of the system was created using Autodesk Inventor. The

overall model is shown in Figure B.1. Note, the gas collection membrane has been omited for clarity.

All drawings were created using Autodesk Inventor, and are presented in the following pages.

Figure B.1: Overall CAD model of prototype

114

Date:

Drawn By:

Part/Assembly:

Projection:

Project:

Sheet:

05-Aug-2014

James Bass

Overall Assembly

Biodigester Toilet

2095.00

2520.00

570.00

1348.00

1 of 2

PARTS LIST

DESCRIPTIONPART NUMBERQTYITEM

First Tank11

Second Tank12

50mm PVC ball valve23

300mm length50mm dia PVC pipe14

25mm dia ball valve26

100mm length25mm dia PE blueline pipe27

25mm dia 90deg bend28

25mm dia PE T-piece19

55mm length25mm dia blueline PE pipe110

1355mm length25mm blueline PE pipe111

Sheet:

Projection:

Project:

Part/Assembly:

Drawn By:

Date:

Iso

05-Aug-2014

James Bass

Overall Assembly

Biodigester Toilet

2 of 2

1

2

11

8

9

8

6

NOTE: Gas collection bladder and framework not shown

Date:

Drawn By:

Part/Assembly:

Projection:

Project:

Sheet:

05-Aug-2014

James Bass

First Tank

1 of 2

Biodigester Toilet

760.00

100.00

1200.00

1950.00

265.00

150.00

490.00

170.00

PARTS LIST


Inlet Assembly13

First Tank Basic14

50mm tank flange19

Outlet Assembly110

First Tank Lid111

Sheet:

Projection:

Project:

Part/Assembly:

Drawn By:

Date:

Iso

9

3

4

05-Aug-2014

Biodigester Toilet

James Bass

First Tank

2 of 2

10

11

Date:

Drawn By:

Part/Assembly:

Projection:

Project:

Sheet:

05-Aug-2014

James Bass

Biodigester Toilet

Second Tank

1 of 2

1900.00

934.00

900.00

760.00

100.00

265.00

PARTS LIST


Second Tank Basic11

50mm tank flange12

Outlet assembly14

Second Tank Lid15

Sheet:

Projection:

Project:

Part/Assembly:

Drawn By:

Date:

Iso

05-Aug-2014 Biodigester Toilet

James Bass

Second Tank

2 of 2

2

1

4

5

PARTS LIST


90mm 90deg PVC bend21

1500mm length90mm dia PVC Pipe13

90mm dia pipe short14

Date:

Drawn By:

Part/Assembly:

Projection:

Project:

Sheet:

1340.00

90.00Ø

90.00Ø

1200.00

150.00

1

1

3

4

05-Aug-2014

James Bass

Inlet Assembly

Biodigester Toilet

1 of 1

Date:

Drawn By:

Part/Assembly:

Projection:

Project:

Sheet:

18-Oct-2014

Biodigester Toilet

James Bass

First Tank Lid

1 of 2

490.00

480.00

490.00

480.007.00

6.00

5.00 16X

125.0090.00

PARTS LIST


7mm ThickExterior Plywood11

25mm Tank Flange12

6mm ThickNeoprene Rubber13

Sheet:

Projection:

Project:

Part/Assembly:

Drawn By:

Date:

Iso

1

3

2

18 Oct 2014

James Bass

Biodigester Toilet

First Tank Lid

2 of 2

Date:

Drawn By:

Part/Assembly:

Projection:

Project:

Sheet:

18 Oct 2014

James Bass

Biodigester Toilet

Second Tank Lid

1 of 2

250.00

190.00

185.00

7.00

6.00

25.00

5.00 8X

5.00 8X

PARTS LIST


PE 185mm dia11

25mm Tank Flange12

7mm ThickPlywood Ring13

6mm ThickNeoprene Seal14

Sheet:

Projection:

Project:

Part/Assembly:

Drawn By:

Date:

Iso

1

3

4

2

18 Oct 2014

Biodigester Toilet

James Bass

Second Tank Lid 2 of 2

Appendix C

Australian Standards for Polyethylene

Pipes

Relevant Standards regarding polyethylene pipes for pressure applications. Taken from AS/NZS 4130:

Polyethylene (PE) Pipes for Pressure Applications (Australian Standards 2009).

126

APPENDIX C. AUSTRALIAN STANDARDS FOR POLYETHYLENE PIPES 127



Appendix D

Australian Standard Gas System

Design Factors

Relevant standards regarding gas distribution design factors. Taken from AS 4645-2005 Gas distribu-

tion network management (Australian Standards 2005).

130

APPENDIX D. AUSTRALIAN STANDARD GAS SYSTEM DESIGN FACTORS 131

Appendix E

Stirrer CAD Drawings

A Computer Aided Design (CAD) model of the stirrer was created using Autodesk Inventor. The

overall model is shown in Figure E.1. All drawings were created using Autodesk Inventor, and are

presented in the following pages.

Figure E.1: Overall CAD model of stirrer

132

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

17/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010101

Lid

THIRD ANGLE PROJECTION

PROJECT

1587 - The Design and Build of a Biodigester

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

10/08/2014

-

Plywood, Sheathing1

UNLESS STATED OTHERWISE

GENERAL TOLERANCE:

LINEAR: ANGULAR:

0.3

1REMOVE BURRS & SHARP EDGES

ALL OVER.

3.2

NOTES.

1. ALL WELDING TO COMPLY WITH AS/NZS 1554.1-2004 - STRUCTURAL STEEL WELDING -

WELDING OF STEEL STRUCTURES.

2. VISUAL INSPECTION OF WELD ONLY.

NOTES.

1. ALL INTERNAL BEND RADII, R?? UNLESS STATED OTHERWISE.

2. TOTAL QUANITITY: 6. (3 RH, 3 LH(SYMETRICALLY OPPOSITE))

NOTE:

1. MAKE FROM: PLYWOOD 7mm. Bunnings.

108 Railway Terrace, Mile End SA 5031.

2. ALTER A SHOWN.

40

9 M8

(

8.98

9.00

)

2×

EQUISPACED @28 PCD

400

400

7.00

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

17/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010102

Shaft


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

10/08/2014

-

Steel, Carbon1


GENERAL TOLERANCE:

LINEAR: ANGULAR:

0.3


ALL OVER.

3.2

NOTES.




NOTES.



NOTES:

1. MAKE FROM: 25 NB - SCH 80 (4.55mm wall) Extra Strong Water Pipe

SA Steel Works. 26 Athol St, Athol Park SA 5012.

2. ALTER AS SHOWN.

33.4( )

24.3( )

31.75 m6

(

31.759

31.775

)

1800

1900

NOTE: Press Fit to Shortlube Bushings

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

19/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010103

Seal


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

10/08/2014

-

Rubber, Silicone1


GENERAL TOLERANCE:

LINEAR: ANGULAR:

0.3


ALL OVER.

3.2

NOTES.




NOTES.



6.00

NOTES:

1. MAKE FROM: 5mm Red Silicone Sheet

Fitch Rubber. 2 George Street, Hindmarsh SA 5007. Part Number: MAT5.0SIL

2. ALTER AS SHOWN

80

31.75

9.00 M8

(

8.98

9.00

)

EQUISPACED @28 PCD

A-A ( 1 : 1 )

A

A

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

17/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010104

Housing


PROJECT

Biodigester Stirrer

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

10/08/2014

-

AL ALLOY, SERIES 5000-6000 1


GENERAL TOLERANCE:

LINEAR: ANGULAR:

0.3


ALL OVER.

3.2

NOTES.




NOTES.



55

9.00 M8

(

8.98

9.00

)

2×

EQUISPACED @28 PCD

76 (stock)

2×45°

38.10 H11

(

38.10

38.26

)

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

17/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010107

Metal Plate(×2)


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

10/08/2014

STEEL, LOW CARBON


GENERAL TOLERANCE:

LINEAR: ANGULAR: REMOVE BURRS & SHARP EDGES

ALL OVER.

NOTES.




NOTES.



7 (Stock)

9.00 M8

(

8.98

9.00

)

8.5

100

50

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

30/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010303

L Joint


PROJECT

Biodigester Stirrer (Project #1587)

SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

1/08/2014

Stainless Steel


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



25

80

88

104×

24

61

8

8.00

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

30/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010304

Bar


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

1/08/2014

Steel


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



310

30

30

14

53

5

5

12.5

15

106×

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

30/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010302

Large Aluminium Paddle


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

1/08/2014

Aluminum 6061


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



425

5

300

30

72

249

281

18

20

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

30/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010301

Small Aluminium Paddle


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

1/08/2014

Aluminum 6061


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



5

300

190

108×

20

20

30

72

249

281

B ( 0.2 : 1 )

C-C ( 0.2 : 1 )

PARTS LIST

QTYDESCRIPTIONPART NUMBERITEM

1Lid1587-0101011

1Shaft1587-0101022

1Seal1587-0101033

1Housing1587-0101044

1Bushing (hidden). Shortlube. Pt

Num: C4048-2

1587-0101055

1Flange Bushing. Shortlube. Pt Num:

C4048-1

1587-0101066

2Metal Plate1587-0101077

6L Bracket1587-0101088

6Bar1587-0101099

1Paddle (large)1587-01011010

2Paddle (small)1587-01011111

B

C

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

3/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

010100

Stirrer Minus Handle


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

1/08/2014


GENERAL TOLERANCE:


ALL OVER.

1

2

3

4

5

6

7

8

9

10

11

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

19/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010201

Handle Arm


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

10/08/2014

STEEL, LOW CARBON


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



5(stock)

400

60

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

3/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010202

Handle Sleeve


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

25/08/2014

STEEL, LOW CARBON


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



41

32

30

30

6 M6

17

NOTE: Threaded hole to fix shaft to handle.

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

19/08/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

1587-010203

Handle Bar


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

10/08/2014

STEEL, LOW CARBON


GENERAL TOLERANCE:


ALL OVER.

NOTES.




NOTES.



30(stock)

120

PARTS LIST

QTYDESCRIPTIONPART NUMBERITEM

1Handle Arm1587-0102011

1Handle Sleeve1587-0102022

1Handle Bar1587-0102033

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

3/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

010200

Handle Assembly


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

31/08/2014

Steel, Carbon


GENERAL TOLERANCE:


ALL OVER.

NOTES.

1. ALL WELDING TO COMPLY WITH AS/NZS 1554.1-2004 -

STRUCTURAL STEEL WELDING -



NOTES.



25

35

30

7

7

B ( 0.25 : 1 )

B

PARTS LIST

QTYPART NUMBERITEM

1Stirrer Sub-Assembly1

1Handle Sub-Assembly2

1

1

2

2

3

3

4

4

5

5

6

6

A A

B B

C C

D D

30/09/2014

DESIGNED

CHECKED

APPROVED

DATE

SHEET

A3

REVISION

1

1 of 1

PART NUMBER

TITLE

100000

Whole Stirrer Assembly


PROJECT


SCALEMASS

DO NOT SCALE

DIMENSIONS IN

MILIMETERS

DRAWING STANDARD

AS1100

MATERIAL QTY

N/A

DRAWN

Charlie Savory

DATE

DATE

DATE

Charlie Savory

1/08/2014


GENERAL TOLERANCE:


ALL OVER.

1

2

Appendix F

Risk Assessment

Risk

Type Specific RiskLikelihood Consequence Risk Level Accept/Reject Prevention/Reduction

Risks To

Project

Success

Cannot Source Feedstock:

Without feedstock prototype

testing is impossible

D 4 Medium RAll team members to contact

potential suppliers immediately

Feedstock Quality: Feedstock

may not contain adequate volatile

solids for the production of biogas

E 2 Low A

148

APPENDIX

F.RISK

ASSESSMENT

149

Anaerobic Digestion Does Not

Occur: Bacteria required for

anaerobic digestion do not form to

useful levels, prohibiting the

production of biogas

D 4 Medium R

Initiate anaerobic digestion process

in smaller external tanks to

guarantee the digestion process is

occurring

Climate: The anaerobic digestion

process may be retarded by

Adelaide’s winter climate

A 3 High R

Install insulation around the

biodigester structure to raise the

internal temperature of the system

Scum Formation: Blockages

occur due to foam and scum

formation, caused by departure of

pH from neutral levels

C 2 Medium R

Macerate feedstock prior to

entering the system, ensure

pipework and fittings are of a

suitable diameter, and prevent

foreign materials from entering the

system by using covers on all inlets

Fire or Explosion: Stored

flammable gas creates a risk of fire

or explosion, causing irreparable

damage

E 5 Medium R

The system will be stored in a well

ventilated area. Warning signs will

be installed to prevent the use of

naked flames and smoking in the

vicinity. The gas storage membrane

will be placed in a location to

prevent unauthorised access

APPENDIX

F.RISK

ASSESSMENT

150

Gas Leaks: Cause a loss of biogas

effecting the results of testingC 2 Medium R

Continuous checking of the system

for leaks using detergent and

water. Correct gas fittings, and

joining methods will also be used

Sludge Leaks: Causes feedstock

to be lost from the system,

retarding gas production

E 2 Low A

Damage to Tanks: Tanks are a

critical and expensive design

components, damage could occur in

transport, construction and testing

D 3 Medium R

Extreme care will be taken during

transportation, construction and

testing. Suitable tools and methods

will be used during construction

after extensive planning

Damage to Plumbing Fixtures:

May be damaged during

construction

E 2 Low A

Part Sourcing: Lead-times and

part availability could cause delays

in construction and testing

C 2 Medium R

Local suppliers used as much as

possible. Parts with long lead-times

will be ordered as soon as possible

Sponsorship: Required

sponsorship is not obtainedD 3 Medium R

A sponsorship prospectus is to be

produced. Potential sponsors will

be continually contacted for the

duration of the project

APPENDIX

F.RISK

ASSESSMENT

151

Google Drive Fails: Google

Drive is used to store and share

project files. If this application

failed files would be lost

E 4 High R

Periodic backups up of the Google

Drive folder will be performed by

all team members

No Available Location for

Testing: Testing will be

impossible without a suitable

location to house the prototype

E 5 High R

Attain necessary approvals and

safety documentation to satisfy

land owners. Continuously contact

potential stakeholders until a

location is found

Team Member Incapacitated:

Illness, injury or unforeseen

circumstances may prevent a team

member from contributing to the

project

D 2 Low A

Risks To

Personal

Safety

Disease Contraction from

Feedstock: Faeces used as

feedstock may contain harmful

pathogens presenting risk of disease

E 4 Medium R

Use of personal protective

equipment, biological waste

handling training will be

undertaken, and a standard

operating procedure will be

developed to minimise user

exposure to feedstock

APPENDIX

F.RISK

ASSESSMENT

152

Fire and Explosion: Flammable

gas is stored within the system

posing a risk of fire and explosion

to local occupants

E 5 High R

The system will be stored in a well

ventilated area. Warning signs will

be installed to prevent the use of

naked flames and smoking in the

vicinity. The gas storage membrane

will be placed in a location to

prevent unauthorised access

Asphyxiation: Biogas contains a

mixture of gases that displace air,

creating a risk of asphyxiation to

local occupants

E 3 Medium RStore system in a well ventilated

area to prevent accumulation of gas

Construction: Lifting heavy

objects and the use of power and

cutting tools during prototype

construction poses a risk of injury.

D 3 Medium R

Ensure all team members wear

PPE, are trained in the use of all

tools, and all power tools are

electrically tested and tagged.

Correct heavy lifting procedures

will be followed. A first aid kit

must always be on site

Appendix G

Project Cost Matrix

153

INVENTORY & BUDGET

Inventory

Item Date Purchased Supplier Quantity Cost Discount Total Cost Savings Type

Aire Toilet Bowl 25-07-2014 Caroma 1 236.30 236.30 0.00 236.30 Toilet

Aire Cistern + Seat 25-07-2014 Caroma 1 212.10 212.10 0.00 212.10 Toilet

Supel Gas Bags 01-09-2014 Mike Hatch 4 16.00 16.00 0.00 64.00 Testing

Litmus Universal Indicator Test Strips x 80 16-09-2014 eBay 1 2.48 2.48 0.00 Testing

Gas Storage Bag 05-08-2014 Puxin 1 175.00 175.00 0.00 System

1200L Water Tank 25-06-2014 Mitre10 2 400.00 200.00 400.00 400.00 System

Plumbing Ball Valve 28-08-2014 Mitre10 1 36.30 36.30 0.00 System

Tank Flange 28-08-2014 Mitre10 2 15.00 30.00 0.00 System

Nipple Hex 25mm 06-08-2014 Mitre10 1 2.25 2.25 0.00 System

Tank Fitting Female 25mm 06-08-2014 Mitre10 1 12.95 12.95 0.00 System

Ball Valve -25mm ART 220PP LH 06-08-2014 Mitre10 1 24.95 24.95 0.00 System

Elbow Poly Met Thread 25x1" ALPRENE 06-08-2014 Mitre10 1 6.95 6.95 0.00 System

Bend DWV PLN M F 100mm x 88DEG 14-08-2014 Mitre10 1 9.50 5.60 3.90 5.60 System

Ball Valve - 15mm ART 220PP LH 14-08-2014 Mitre10 3 12.95 6.72 18.69 20.16 System

Tank Fitting Female 15mm 14-08-2014 Mitre10 2 10.50 5.18 10.64 10.36 System

Tee Metric Female 20mmx3/4" ALPRENE 14-08-2014 Mitre10 1 9.95 5.16 4.79 5.16 System

Nipple Hex Reducing 20x15mm 14-08-2014 Mitre10 4 1.99 1.29 2.80 5.16 System

Connector End F/A 20 X3/4 ALPRENE 14-08-2014 Mitre10 1 5.95 3.45 2.50 3.45 System

Elbow Poly Met Thread 20x20mm ALPRENE 14-08-2014 Mitre10 1 6.50 3.28 3.22 3.28 System

Elbow Poly 20mm ALPRENE 14-08-2014 Mitre10 1 8.95 4.53 4.42 4.53 System

Socket Reducer 100mmx90mm 14-08-2014 Mitre10 1 9.99 5.85 4.14 5.85 System

Pipe 20mm PE100 PN 12 5-25M BLUE STRIPE (0.16m) 14-08-2014 Mitre10 0.16 57.99 34.43 3.77 5.51 System

Suction Hose 50mm Grey Per Metre 14-08-2014 Mitre10 1 16.92 16.92 0.00 System

Director 50mm (Lump End) 1068 14-08-2014 Mitre10 2 7.13 14.27 0.00 System

Pipe PVC SW 90MM P/M 28-08-2014 Mitre10 1.5 3.99 1.63 3.54 2.45 System

Cap Push On DMW 100mm 28-08-2014 Mitre10 1 4.50 2.06 2.44 2.06 System

Bend Stormwater FF 90mm x 90deg 28-08-2014 Mitre10 1 2.25 1.16 1.09 1.16 System

Solvent Cement Type N Blue 125ML 28-08-2014 Mitre10 1 4.99 2.44 2.55 2.44 System

Brush Paint White 25mm 28-08-2014 Mitre10 1 1.25 0.84 0.41 0.84 System

Priming Fluid Red 28-08-2014 Mitre10 1 4.99 2.23 2.76 2.23 System

Silicone Roof Trans 300g BUY RIGHT 28-08-2014 Mitre10 1 4.99 0.88 4.11 0.88 System

Screw L/THRD CS SS 8GX30 PK8 28-08-2014 Mitre10 2 4.25 2.73 3.04 5.46 System

Socket Hex Brass 3/4 81514 01-09-2014 Mitre10 1 2.95 1.30 1.65 1.30 System

Nipple Brass ALL THRD 3/4X6 01-09-2014 Mitre10 2 11.95 6.30 11.30 12.60 System

Plumbing Ball Valve 01-09-2014 Mitre10 1 57.95 21.65 36.30 21.65 System

Bib Cock 20mm LH 01-09-2014 Mitre10 2 23.95 10.82 26.26 21.64 System

Tape Teflon White 12x0.075mmx10m 01-09-2014 Mitre10 1 0.99 0.71 0.28 0.71 System

Tube Vinyl Clear 25mmx25m Coil Neta 30-09-2014 Mitre10 0.5 6.50 0.51 3.00 0.26 System

Neoprene Rubber 1200 x 4.5mm 28-08-2014 Fitch the Rubber Man 1 133.76 133.76 0.00 System

Plywood 6mm 900 x 600 04-09-2014 Mitre10 1 14.99 2.25 12.74 2.25 System

Screws (Pack of 8) 04-09-2014 Mitre10 2 4.25 0.85 6.80 1.70 System

Silicone Rubber 1200 x 6mm 27-08-2014 Fitch the Rubber Man 1 18.00 18.00 0.00 Stirrer

Seamless Pipe Schedule 80 ASTM A106 27-08-2014 Metalcorp 2 15.38 30.76 0.00 Stirrer

Leaf strainer cover 400 or 500mm 27-08-2014 Maxiplas 2 11.00 22.00 0.00 Stirrer

Bushing Sleeve Sintere C4048-2 03-09-2014 CBC Motion 1 18.29 18.29 0.00 Stirrer

Bushing Sleeve Sintere F4048-1 03-09-2014 CBC Motion 1 18.60 18.60 0.00 Stirrer

Ply Wood 03-09-2014 Bunnings Mile End 1 9.43 9.43 0.00 Stirrer

Leaf strainer cover 400 or 500mm 03-09-2014 Maxiplas -1 11.00 -11.00 0.00 Stirrer

Hose with Gun 15mm 30-09-2014 Mitre10 (Domain) 1 5.80 5.80 0.00 Operation

Tape Teflon Yellow Gas 12mmx10m BOSTON 06-08-2014 Mitre10 1 3.95 3.95 0.00 Operation

Tape Teflon Yellow Gas 12mmx10m BOSTON 14-08-2014 Mitre10 1 3.95 2.50 1.45 2.50 Operation

Tape Teflon Pink Gas 12mmx6m BOSTON 01-09-2014 Mitre10 1 3.95 2.35 1.60 2.35 Operation

Tape Teflon Yellow Gas 12mmx10m BOSTON 09-09-2014 Mitre10 1 3.95 0.20 3.75 0.20 Operation

Funnel Black Plastic w/strainer 17cm 30-09-2014 Mitre10 1 5.99 0.60 5.39 0.60 Operation

Tape Teflon White 12x0.075mmx10m 30-09-2014 Mitre10 1 0.99 0.10 0.89 0.10 Operation

Plastic Bucket 10L 11-09-2014 Mitre10 2 1.50 3.00 0.00 Operation

Disposable Gloves 11-09-2014 Mitre10 1 5.99 0.60 5.39 0.60 Operation

Funnel 10" 28-08-2014 Paramount Browns 1 9.95 9.95 0.00 Operation

Bioballs (150) 04-08-2014 Hahndorf Aquarium 1 35.01 35.01 0.00 Operation

Tape Duct Silver 48mm X 30m 09-10-2014 Mitre10 1 4.50 0.34 4.16 0.34 Operation

Glove Handy Disposable Pk24 09-10-2014 Mitre10 1 5.99 0.45 5.54 0.45 Operation

Coke Drum - 76L Paramount Browns 2 6.00 12.00 0.00 Miscellaneous

Coke Drum - 76L 09-09-2014 Paramount Browns 4 7.50 30.00 0.00 Miscellaneous

Coke Drum - 76L 28-08-2014 Paramount Browns 2 7.50 15.00 0.00 Miscellaneous

Fortecon 200um 2m Wide Per Metre 09-09-2014 Mitre10 1 3.50 0.52 2.98 0.52 Miscellaneous

Tape Gaffa HD Gorilla 48mm x 11m 09-09-2014 Mitre10 1 10.50 1.05 9.45 1.05 Miscellaneous

Silicone Roof Trans 300g BUY RIGHT 09-09-2014 Mitre10 1 4.99 4.99 0.00 Miscellaneous

Valve Greenback 13mm 09-09-2014 Mitre10 1 3.99 0.80 3.19 0.80 Miscellaneous

Joiner 13mm 09-09-2014 Mitre10 4 0.40 0.06 1.36 0.24 Miscellaneous

Adaptor Poly Tee 09-09-2014 Mitre10 3 0.65 0.13 1.56 0.39 Miscellaneous

Polytube 13mm Per Metre 09-09-2014 Mitre10 1 0.70 0.14 0.56 0.14 Miscellaneous

Joiner 13mm 09-09-2014 Mitre10 -4 0.40 -1.60 0.00 Miscellaneous

Adaptor Poly Tee 09-09-2014 Mitre10 -1 0.65 -0.65 0.00 Miscellaneous

Tank Fitting Black 15mm 09-09-2014 Mitre10 3 6.95 20.85 0.00 Miscellaneous

Total 95.16 1,324.61 1,071.36

Budget

Type

Allocated Budget Adelaide University 5 200.00 1,000.00

Sponsorship Lynair Logistics 1 300.00 300.00

Total 1,300.00

Remaining -24.61

Appendix H

Sponsorship Prospectus

155

A Biodigester Toilet

For the Developing World

Honours Project Sponsorship Prospectus

The Challenge:

As of 2012, 1.1 billion people still defecate in the open and 2.6 billion people do not have access

to improved sanitation facilities. In many parts of the world, waste from open defecation is likely to be washed into local rivers, which are generally primary sources for drinking, cooking, cleaning

and other household tasks. Bacterial and viral contamination of water supplies in both rural and

urban environments can result in diseases such as diarrhoea, leading to fatal consequences.

Another problem faced by many regions of low income is access to energy sources for cooking,

lighting, and other basic human needs. In 2004, the number of people worldwide relying on biomass resources as their primary fuel for cooking was recorded to be just over 2.5 billion. The

practice of burning biomass in such communities has been documented by the Organisation for Economic Cooperation and Development as one of the most common causes of death and

respiratory health problems. Recent figures show that more than 4 million people die prematurely from illness as a result of the household air pollution created during cooking with

solid fuels.

The Solution:

A biodigester is designed to produce biogas using anaerobic digestion of human and animal

waste. Depending on the efficiency of the system and quality of feedstock, biodigesters have the

potential to produce a reliable supply of biogas gas that is of a suitable quality to fuel gas stoves

and lamps. By incorporating a toilet into the digester design, we aim to alleviate some of the health

and sanitation problems resulting from open defecation as well as the respiratory health

problems stemming from the inhalation of household air pollution produced by burning biomass.

Who are we?

A group of five motivated University of Adelaide students from the School of Mechanical

Engineering who are passionate about improving sanitation in communities exposed to open

defecation. The project team aims to alleviate challenges faced on a daily basis in the developing

world by designing and building a prototype for future implementation. The well organised and

cohesive team is led by project manager James Bass. As a team, students James, Nishanth Cheruvu,

Natasha Rayan, Charlie Savory and Kieran Sheehan will lead design and assembly of the

biodigester toilet.

The School of Mechanical Engineering provides academic support through school staff and access

to workshop facilities. Project supervisor Dr Cristian Birzer has led many successful projects in the past including last year’s award-winning low-emission cook stove for the developing world.

How would this project benefit from sponsor contributions?

Because the final product will have humanitarian applications in lower-income countries, our

objective is to minimise costs of the design by integrating recycled items. Sponsorship of any items

pertaining to the project would be much appreciated. The design will consist of:

Two large cylindrical tanks

Wooden framework

Heavy duty polyethylene bags for gas collection

A flame trap

A functional toilet system

PVC Pipes and

Various fittings.

Subsequent to completion of testing, there will be a supply of hazardous effluent and flammable

methane gas produced as by-products of the digestion process. It is of paramount importance

that these substances are used or discarded in a manner that is safe and does not damage the

natural environment. Support or advice regarding the disposal of such wastes is very welcome.

Finally, any funding towards the project will be put towards sourcing components and services

that aren’t directly obtained through sponsors. Monetary sponsorship is an instrumental

contribution to the success of the project as student project funding through the university is

strictly limited.

What happens once the biodigester toilet is completed?

The prototype will be on display at MechExpo which is a School of Mechanical Engineering final

year project showcasing event. This year marks the 20th annual exhibition and will attract

attention from representatives throughout the engineering industry. Awards will be presented to

standout projects in recognition of student accomplishments. Mechexpo is also a great

educational event for students and teachers because it provides a unique opportunity to

encounter engineering in practice and engage with the engineers of tomorrow. It is very likely

that this event will attract media attention and has been featured in various news programs,

websites and newspapers in the past. The MechExpo will take place on the Wednesday the 29th

and Thursday the 20th of October.

With success of the project, an implementation strategy will be established to promote the biodigester toilet in developing communities. Should the prototype require further

developments, a future project team may choose to continue the project and make amendments.

How will sponsors be promoted?

Promotion of sponsors will be through print media displayed at our stand during MechExpo.

Contributions towards the project will be acknowledged during the Seminar Presentation and in the final report. Standout contributions will benefit from further advertisement in the form of

logos displayed on the finished product and other benefits to be discussed on a case by case basis.

Sponsor representatives are invited to attend both the Seminar and MechExpo. Exact dates of the

seminar presentation are yet to be advised.

Appendix I

Project Hours Spent by Individual

Team Members

158

Month Student Time Cost

January Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

15 1 1 0 5 0 7 175

16 2 0 0 5 0 7 175

17 [1] 1 1 1 1 1 5 125

18 0 0 0 0 0 0 0

19 1 1 0 0 1 3 75

20 0 1 0 0 0 1 25

21 0 1 0 1 2 4 100

22 2 1 0 2 0 5 125

23 2 2 0 0 2 6 150

24 1 1 1 1 1 5 125

25 4 2 0 0 4 10 250

26 0 0 0 0 0 0 0

27 2 0 0 0 0 2 50

28 0 2 0 2 1 5 125

29 0 2 0 2 0 4 100

30 1 1 1 0 3 6 150

31 1 1 1 1 1 5 125

Month Total 18 17 4 20 16 75 1875

Year to Date 18 17 4 20 16 75 1875


February Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 2 0 0 2 0 4 100

2 2 0 0 0 2 4 100

3 0 0 0 2 1 3 75

4 1 3 0 0 1 5 125

5 1 1 1 1 1 5 125

6 1 2 0 0 0 3 75

7 1 1 1 1 1 5 125

8 0 0 0 0 0 0 0

9 0 1 0 0 3 4 100

10 1 1 0 0 0 2 50

11 2 1 0 0 2 5 125

12 2 1 0 2 0 5 125

13 0 3 2 2 1 8 200

14 1 1 1 1 1 5 125

15 0 0 0 0 0 0 0

16 3 0 0 1 1 5 125

17 1 3 0 0 0 4 100

18 0 1 0 2 2 5 125

19 2 1 0 0 1 4 100

20 3 2 0 2 0 7 175

21 2 1 0 2 0 5 125

22 3 0 0 0 3 6 150

23 1 1 0 0 0 2 50

24 1 1 1 1 1 5 125

25 0 3 0 0 0 3 75

26 0 0 0 2 1 3 75

27 1 1 0 1 0 3 75

28 0 1 0 0 0 1 25

Month Total 31 30 6 22 22 111 2775

Year to Date 49 47 10 42 38 186 4650


March Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 1 0 0 0 0 1 25

2 1 1 0 2 0 4 100

3 [2] 3 1 4 1 1 10 250

4 2 1 2 0 2 7 175

5 3 1 1 1 1 7 175

6 1 1 3 0 0 5 125

7 1 1 1 1 1 5 125

8 0 1 0 0 0 1 25

9 0 0 0 3 3 6 150

10 0 0 0 2 0 2 50

11 1 1 1 1 1 5 125

12 2 1 3 0 0 6 150

13 2 1 0 0 0 3 75

14 2 1 2 0 1 6 150

15 2 2 0 0 0 4 100

16 0 0 0 2 2 4 100

17 0 1 1 2 0 4 100

18 0 1 2 0 0 3 75

19 [3] 1 1 1 1 1 5 125

20 0 1 3 0 0 4 100

21 1 1 1 1 1 5 125

22 0 0 0 0 0 0 0

23 0 0 0 0 2 2 50

24 4 2 1 3 3 13 325

25 3 1 1 1 1 7 175

26 1 1 3 1 1 7 175

27 0 0 0 0 0 0 0

28 1 1 1 1 1 5 125

29 0 2 0 0 3 5 125

30 3 2 0 0 0 5 125

31 2 2 2 0 0 6 150

Month Total 37 29 33 23 25 147 3675

Year to Date 86 76 43 65 63 333 8325


April Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 0 4 2 2 3 11 275

2 0 2 1 3 2 8 200

3 2 2 3 2 1 10 250

4 1 1 1 1 1 5 125

5 3 1 4 4 2 14 350

6 2 2 2 2 0 8 200

7 1 2 1 3 1 8 200

8 1 1 0 1 1 4 100

9 2 1 1 1 2 7 175

10 [4] 1 1 1 1 1 5 125

11 1 3 2 1 1 8 200

12 2 3 3 1 2 11 275

13 1 2 1 3 3 10 250

14 2 3 1 1 1 8 200

15 1 1 2 2 4 10 250

16 0 0 0 3 1 4 100

17 0 0 2 4 2 8 200

18 2 1 4 1 1 9 225

19 4 2 1 3 0 10 250

20 0 2 0 0 0 2 50

21 2 1 2 3 3 11 275

22 1 1 2 1 1 6 150

23 0 0 2 0 3 5 125

24 2 0 2 1 0 5 125

25 2 1 2 2 2 9 225

26 3 2 2 4 0 11 275

27 2 1 1 3 1 8 200

28 3 1 1 1 1 7 175

29 2 3 1 1 2 9 225

30 0 2 1 2 2 7 175

Month Total 43 46 48 57 44 238 5950

Year to Date 129 122 91 122 107 571 14275


May Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 0 1 1 1 1 4 100

2 0 2 2 2 2 8 200

3 2 0 3 0 1 6 150

4 1 0 0 1 3 5 125

5 2 0 2 3 0 7 175

6 2 4 4 4 4 18 450

7 1 1 1 1 1 5 125

8 0 0 2 0 1 3 75

9 [5] 0 1 1 1 1 4 100

10 2 2 4 1 2 11 275

11 2 3 1 4 1 11 275

12 0 2 0 3 2 7 175

13 0 1 5 2 3 11 275

14 3 0 1 4 1 9 225

15 3 0 0 1 2 6 150

16 0 2 0 2 3 7 175

17 0 3 2 2 0 7 175

18 2 1 1 3 3 10 250

19 1 0 2 1 2 6 150

20 2 1 4 6 0 13 325

21 1 0 2 8 1 12 300

22 1 1 2 8 1 13 325

23 2 2 2 1 2 9 225

24 1 3 3 2 0 9 225

25 2 4 2 4 3 15 375

26 2 2 6 8 4 22 550

27 3 1 4 2 0 10 250

28 3 2 6 4 2 17 425

29 2 3 2 2 1 10 250

30 2 0 3 3 1 9 225

31 4 2 6 2 2 16 400

Month Total 46 44 74 86 50 300 7500

Year to Date 175 166 165 208 157 871 21775


June Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 2 2 3 2 1 10 250

2 3 0 2 1 3 9 225

3 1 1 1 4 3 10 250

4 1 1 1 4 5 12 300

5 4 4 4 4 4 20 500

6 0 5 5 3 3 16 400

7 0 5 3 3 0 11 275

8 2 1 5 1 0 9 225

9 1 4 2 0 5 12 300

10 1 5 5 5 4 20 500

11 2 3 1 3 0 9 225

12 3 0 1 2 1 7 175

13 4 1 3 4 2 14 350

14 1 5 1 1 4 12 300

15 0 1 1 1 4 7 175

16 1 2 4 2 1 10 250

17 0 5 1 5 4 15 375

18 0 5 1 3 5 14 350

19 2 1 5 4 0 12 300

20 3 5 2 2 3 15 375

21 1 3 2 2 4 12 300

22 3 2 3 5 4 17 425

23 1 1 4 0 4 10 250

24 2 0 5 1 1 9 225

25 3 1 4 4 3 15 375

26 0 2 4 3 5 14 350

27 0 0 2 5 2 9 225

28 1 0 4 0 1 6 150

29 2 0 5 5 2 14 350

30 0 3 0 0 4 7 175

Month Total 44 68 84 79 82 357 8925

Year to Date 219 234 249 287 239 1228 30700


July Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 0 3 0 1 0 4 100

2 4 1 0 3 5 13 325

3 4 0 0 1 3 8 200

4 3 1 0 2 1 7 175

5 2 2 0 0 4 8 200

6 1 2 2 4 3 12 300

7 5 2 0 3 3 13 325

8 3 2 0 3 5 13 325

9 1 2 2 5 4 14 350

10 4 2 1 1 3 11 275

11 5 4 2 4 1 16 400

12 4 3 4 1 0 12 300

13 0 0 3 3 0 6 150

14 4 3 1 1 4 13 325

15 2 0 0 4 4 10 250

16 1 3 1 1 2 8 200

17 3 2 1 2 3 11 275

18 0 4 0 3 3 10 250

19 5 0 0 0 2 7 175

20 1 3 5 1 1 11 275

21 0 5 5 4 5 19 475

22 2 1 1 4 0 8 200

23 4 2 0 0 2 8 200

24 5 1 0 4 3 13 325

25 1 5 0 5 1 12 300

26 0 0 5 3 4 12 300

27 1 5 3 2 4 15 375

28 5 3 5 0 4 17 425

29 2 3 1 3 2 11 275

30 0 4 0 1 4 9 225

31 2 3 1 0 0 6 150

Month Total 74 71 43 69 80 337 8425

Year to Date 293 305 292 356 319 1565 39125


August Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 2 3 5 2 3 15 375

2 2 2 2 3 5 14 350

3 1 4 5 5 1 16 400

4 4 0 4 4 0 12 300

5 0 2 1 4 0 7 175

6 1 0 5 0 5 11 275

7 5 0 3 4 4 16 400

8 2 0 1 0 5 8 200

9 2 5 0 0 3 10 250

10 4 0 3 4 4 15 375

11 1 3 4 4 5 17 425

12 0 1 0 2 0 3 75

13 3 4 0 4 1 12 300

14 5 5 4 2 2 18 450

15 3 2 5 0 3 13 325

16 0 3 3 2 3 11 275

17 4 4 2 4 5 19 475

18 2 5 4 2 3 16 400

19 5 3 2 2 1 13 325

20 3 0 1 2 4 10 250

21 1 5 2 4 4 16 400

22 3 1 4 0 5 13 325

23 3 0 3 3 3 12 300

24 5 0 3 0 5 13 325

25 4 4 1 1 1 11 275

26 1 4 3 1 2 11 275

27 1 1 0 1 0 3 75

28 2 1 1 4 2 10 250

29 2 4 5 5 3 19 475

30 2 4 0 5 2 13 325

31 1 4 1 4 0 10 250

Month Total 74 74 77 78 84 387 9675

Year to Date 367 379 369 434 403 1952 48800


September Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 2 0 0 4 4 10 250

2 1 2 5 2 5 15 375

3 1 3 0 5 1 10 250

4 1 3 0 0 5 9 225

5 5 4 2 0 0 11 275

6 1 5 1 4 0 11 275

7 1 5 3 5 4 18 450

8 3 0 5 1 4 13 325

9 1 4 1 4 1 11 275

10 5 3 0 3 5 16 400

11 2 5 2 2 1 12 300

12 5 3 1 3 2 14 350

13 2 5 3 0 3 13 325

14 1 4 2 3 5 15 375

15 4 4 5 0 0 13 325

16 5 4 2 5 5 21 525

17 2 1 3 2 3 11 275

18 5 1 2 0 2 10 250

19 5 2 5 0 5 17 425

20 3 2 2 1 1 9 225

21 1 2 1 1 5 10 250

22 5 1 4 2 1 13 325

23 4 3 0 4 0 11 275

24 5 3 5 2 1 16 400

25 5 3 2 4 4 18 450

26 5 1 2 3 1 12 300

27 4 2 4 3 0 13 325

28 5 2 3 4 4 18 450

29 3 1 1 4 5 14 350

30 4 1 0 1 2 8 200

Month Total 96 79 66 72 79 392 9800

Year to Date 463 458 435 506 482 2344 58600


October Bass, James Cheruvu, Nishanth Rayan, Natasha Savory, Charlie Sheehan, Kieren (hrs) ($)

1 4 5 2 4 4 19 475

2 5 1 4 1 0 11 275

3 1 5 2 1 4 13 325

4 0 2 5 3 5 15 375

5 4 5 2 5 4 20 500

6 4 4 4 3 0 15 375

7 4 5 3 0 5 17 425

8 5 1 0 4 5 15 375

9 2 4 2 5 1 14 350

10 4 5 1 0 0 10 250

11 0 0 3 0 5 8 200

12 4 1 1 2 0 8 200

13 0 1 5 2 4 12 300

14 4 4 5 0 5 18 450

15 5 3 3 2 5 18 450

16 5 0 3 1 2 11 275

17 5 4 4 5 4 22 550

18 2 1 2 0 2 7 175

19 5 0 2 1 0 8 200

20 3 4 1 4 3 15 375

21 6 5 6 6 6 29 725

22 12 12 12 12 12 60 1500

23 12 12 12 12 12 60 1500

24 4 4 4 4 4 20 500

Month Total 100 88 88 77 92 445 11125

Year to Date 563 546 523 583 574 2789 69725

Appendix J

SupelTM Sampling Bag Data Sheet

165

Appendix K

Picarro Gas Analyser Data Sheet

168

© 2013 PICARRO, INC. · 3105 Patrick Henry Drive Santa Clara, CA 95054 · T 408.962.3900 · E [email protected] · W www.picarro.com

PICARRO G2201-iCRDS Analyzer for Isotopic Carbon in CO2 and CH4 Simultaneous Insights Into Complex Carbon Source/Sink Behavior of Two Species with One Analyzer

• World’s only field-deployable analyzer capable of simultaneous δ13C measurements for both CO2 and CH4

• Less hassle – Less calibration, less maintenance, no consumables

• Endures harsh environments – mountains, oceans, forests, and tundra

• Excellent precision at a fraction of the operating cost of IRMS

• Picarro analyzers are deployed by thousands of researchers, on all seven continents and in more than 60 countries

Respiration, fermentation. Oxidation, reduction. Source, sink. Carbon dioxide and methane are tightly intertwined in many biological and geological systems. If you know the behavior of only one of these species, you may only know half the story. With the new G2201-i, the isotopic carbon ratio in both CO2 and CH4 can be measured at the same time. This instrument combines the capabilities of Picarro’s two carbon isotope instruments for CO2 and CH4 into a single instrument to gather the insights that stable isotope ratios offer. With this instrument, researchers can follow the carbon as it moves from source to sink.

The G2201-i operates in one of three modes: CO2-only mode, CH4-only mode, and combined CO2/CH4 mode. In the combined mode, the measurement of CO2 and CH4 are interleaved every few seconds to produce a sampling rate that is faster than the gas turn-over time in the cavity. The analyzer’s combined precision is <0.16‰ for δ13C-CO2 and <1.15‰ for δ13C-CH4. The simultaneous measurement ability of the G2201-i is a technology unique to Picarro. When the analyzer is in CO2-only mode or CH4-only mode, the precision improves because more time is devoted to one molecule. For the CO2-only mode, the δ13C-CO2 precision is <0.12‰, which is similar to the precision of our dedicated G2131-i δ13C-CO2 analyzer. For the CH4-only mode, the δ13C-CH4 precision is <0.8‰, which is the same precision as our dedicated G2132-i δ13C-CH4 analyzer.

Methane concentrations vary widely in nature. Atmospheric methane is ~1.8ppm, but methane in the headspace of a water sample can be 1000ppm. To cover this large concentration range, the analyzer has two CH4-only modes. The High Precision mode provides the best precision at ambient and near-ambient concentrations of CH4 up to 12ppm, which is more than 6 times the ambient concentration. The High Range mode provides a dynamic range that goes from ambient concentration at 1.8ppm to 1000ppm. This allows one to select the best option for a given study.

The G2201-i brings simplicity to research. Its small size and robustness make it easy to transport to the field where getting immediate results allows researchers to change course on-the-fly to get the most form a critical field campaign. The G2201-i can be running within minutes out of the box, and can operate for months without user interaction. In all modes, the analyzer precisely measures CO2, H2O, and CH4 concentration, which allows cross-influence of these species to be quantified and corrected, as well as eliminating the need for gas drying. Peripherals such as the Small Sample Isotope Module and the 16-Port Manifold extend the utility of the analyzer. Scientists using these systems have reported the highest quality data, day in and day out, with fewer calibrations than other spectral absorption-based instruments.

© 2013 PICARRO, INC. · 3105 Patrick Henry Drive Santa Clara, CA 95054 · T 408.962.3900 · E [email protected] · W www.picarro.com

Performance Specifications

CO2 Isotope-only mode CH4 Isotope-only mode Simultaneous mode

δ13C Precision (1-σ, 1 Hr window, 5 min. average)δ13C Precision (1-σ, 1 Hr window, 5 min. average)δ13C Precision (1-σ, 1 Hr window, 5 min. average)δ13C Precision (1-σ, 1 Hr window, 5 min. average)

δ13C-CO2 < 0.12 ‰ - < 0.16 ‰

δ13C-CH4 - High Precision mode: < 0.8 ‰High Dynamic Range mode: <0.4‰

High Precision mode: < 1.15 ‰High Dynamic Range mode: < 0.55‰

δ13C Maximum Drift (peak-to-peak, 1 hr average interval average over 24 hrs at STP)δ13C Maximum Drift (peak-to-peak, 1 hr average interval average over 24 hrs at STP)δ13C Maximum Drift (peak-to-peak, 1 hr average interval average over 24 hrs at STP)δ13C Maximum Drift (peak-to-peak, 1 hr average interval average over 24 hrs at STP)

δ13C-CO2 < 0.6 ‰ - < 0.6 ‰

δ13C-CH4 - High Precision and High DynamicRange modes:< 1.5 ‰ at 10 ppm CH4

High Precision and High Dynamic Rangemodes:< 1.5 ‰ at 10 ppm CH4

Concentration Precision (1-σ, 30 sec. average)Concentration Precision (1-σ, 30 sec. average)Concentration Precision (1-σ, 30 sec. average)Concentration Precision (1-σ, 30 sec. average)

CO2 200 ppb + 0.05 % of reading (12C)10 ppb + 0.05 % of reading (13C)

1 ppm + 0.25 % of reading (12C) 200 ppb + 0.05 % of reading (12C)10 ppb + 0.05 % of reading (13C)

CH4 50 ppb + 0.05 % of reading (12C) High Precision mode 5 ppb + 0.05 % of reading (12C) 1 ppb + 0.05 % of reading (13C)High Dynamic Range mode: 50 ppb + 0.05 % of reading (12C) 10 ppb + 0.05 % of reading (13C)

High Precision mode 5 ppb + 0.05 % of reading (12C) 1 ppb + 0.05 % of reading (13C)High Dynamic Range mode: 50 ppb + 0.05 % of reading (12C) 10 ppb + 0.05 % of reading (13C)

H2O 100 ppm100 ppm100 ppm

Dynamic RangeDynamic RangeDynamic RangeDynamic Range

CO2 Guaranteed Spec Range

380-2000 ppm 200-2000 ppm 380-2000 ppm

CO2 Operational Range 100-4000 ppm 0-4000 ppm 100-4000 ppm

CH4 Guaranteed Spec Range

1.8-500 ppm High Precision mode:1.8-12 ppmHigh Dynamic Range mode: 10-1000 ppm

High Precision mode:1.8-12 ppmHigh Dynamic Range mode: 10-500 ppm

CH4 Operational Range 0-1000 ppm High Precision mode:1.2-15 ppmHigh Dynamic Range mode: 1.8-1500 ppm

High Precision mode:1.2-15 ppmHigh Dynamic Range mode: 1.8-1500 ppm

H2O Guaranteed Spec Range

0-2.4 %0-2.4 %0-2.4 %

H2O Operational Range 0-5 %0-5 %0-5 %

Ambient Temperature Dependence

Guaranteed < ± 0.06 ‰ / ºC, typical < ± 0.025 ‰ /ºCGuaranteed < ± 0.06 ‰ / ºC, typical < ± 0.025 ‰ /ºCGuaranteed < ± 0.06 ‰ / ºC, typical < ± 0.025 ‰ /ºC

Measurement Interval ~ 3 secs ~ 3 secs ~ 5 secs

Rise/Fall time (10-90 % / 90-10 %)

Typical ~ 30 secTypical ~ 30 secTypical ~ 30 sec

Applications Considerations

Interference can occur for concentrations of H2O and CO2 well outside of the defined dynamic range, as well as other organics, ammonia, ethane, ethylene, or sulfur containing compounds. Users should verify with prepared lab samples. Please contact us to discuss the experimental conditions. Pressure drops in the instrument’s gas path can draw external air when this system is used in recirculating applications.



Appendix L

Testing Numerical Results

171

Testing & Observations

DateTemperature (°C,

Adelaide Airport, 9am)

Temperature (°C,

Adelaide Airport, 3pm)

Adelaide Airport

Average (°C)

Temperature (°C,

Kent Town, 9am)

Temperature (°C,

Kent Town, 3pm)

Kent Town Average

(°C)BOM Average

Test Time

(approx.)Testing Site Ambient

12/09/2012 13.7 14.7 14.2 13.9 17.2 15.55 14.875 11:00

13/09/2014 14 19.7 16.85 14.5 21.8 18.15 17.5

14/09/2014 18.1 26.2 22.15 19.4 26.1 22.75 22.45

15/09/2014 14.8 15.8 15.3 15 16.2 15.6 15.45

16/09/2014 14.9 15.4 15.15 14.8 16.8 15.8 15.475

17/09/2014 13.7 15.6 14.65 13 16.2 14.6 14.625

18/09/2014 12.4 13.3 12.85 12.1 12.5 12.3 12.575

19/09/2014 15.3 17 16.15 14.7 19.1 16.9 16.525

20/09/2014 18 20.2 19.1 18 22.5 20.25 19.675

21/09/2014 17.3 18.8 18.05 18.7 23.5 21.1 19.575

22/09/2014 20.5 22.6 21.55 20.5 26.2 23.35 22.45 9:00 30

23/09/2014 21.2 22.7 21.95 21.3 25.9 23.6 22.775

24/09/2014 19.4 18 18.7 19.2 21.9 20.55 19.625

25/09/2014 14.8 16 15.4 15.1 15.4 15.25 15.325 10:00 27

26/09/2014 14.3 16.9 15.6 13.1 18.2 15.65 15.625

27/09/2014 21.6 28.7 25.15 22 30.1 26.05 25.6

28/09/2014 25.2 20.1 22.65 25.1 25 25.05 23.85

29/09/2014 16.3 19.6 17.95 15.8 21 18.4 18.175

30/09/2014 18.4 17 17.7 19.3 16.8 18.05 17.875 11:00 28

1/10/2014 14.5 17 15.75 15 17.6 16.3 16.025

2/10/2014 14.5 15.9 15.2 14 17.7 15.85 15.525

3/10/2014 17.9 21.5 19.7 18.4 25.8 22.1 20.9 11:00 24

4/10/2014 24.4 28.8 26.6 24.4 30.9 27.65 27.125

5/10/2014 16.6 22.3 19.45 16.6 25.1 20.85 20.15

6/10/2014 26.6 20.7 23.65 27.8 22.3 25.05 24.35

7/10/2014 14.8 16.3 15.55 14.3 18 16.15 15.85 9:00 20

8/10/2014 12.9 16.9 14.9 12.9 19.4 16.15 15.525

9/10/2014 17.9 27.2 22.55 19.4 27.9 23.65 23.1 9:30 23

10/10/2014 21.6 29.35 25.475 21.8 31.7 26.75 26.1125

11/10/2014 15.7 17.9 16.8 15.2 20.5 17.85 17.325

12/10/2014 14.6 17.3 15.95 14.5 20.6 17.55 16.75

13/10/2014 12 14.7 13.35 12.3 16.1 14.2 13.775 9:00 23

14/10/2014 13.9 15.1 14.5 12.8 15.6 14.2 14.35

15/10/2014 13.2 15.9 14.55 13.1 17 15.05 14.8

16/10/2014 12.6 16.2 14.4 12 18.6 15.3 14.85 10:30 15

17/10/2014 17.4 22.7 20.05 17.2 27.4 22.3 21.175

18/10/2014 24.3 28.8 26.55 24.3 30.8 27.55 27.05

19/10/2014 24.1 28.4 26.25 24.8 30.9 27.85 27.05

20/10/2014 18.3 27.1 22.7 19.3 31.8 25.55 24.125

21/10/2014 29.7 35.8 32.75 28.8 36.9 32.85 32.8 12:00 39

22/10/2014 21.6 22.4 22 27.2 29.1 28.15 25.075

Testing & Observations

Date Testing Site Ambient Effluent Inlet pHEffluent

Temperature (°C)pH Bag # Date analysed Methane (ppm)

Carbon Dioxide

(ppm)Comments

12/09/2012 1 19/09/2014 259.2375685 6300First gas sample taken. Thermometer and litmus paper yet

to be obtained.

13/09/2014

14/09/2014

15/09/2014

16/09/2014

17/09/2014

18/09/2014

19/09/2014

20/09/2014

21/09/2014

22/09/2014 30 21 32 7 1 25/09/2014 1879.879582 40779

23/09/2014

24/09/2014

25/09/2014 27 22 28 7 2 25/09/2014 3580.644796 44517

26/09/2014

27/09/2014

28/09/2014

29/09/2014

30/09/2014 28 21 26 7 1 8/10/2014 8046.674964 14890Tanks removed from greenhouse today, lots of mixing

involved.

1/10/2014

2/10/2014

3/10/2014 24 14 26 6.5 13 5 2 8/10/2014 5123.286122 20123Ph of second tank taken. Expected lower methane, higher

carbon dioxide due to shifting of tanks on 30/09

4/10/2014

5/10/2014

6/10/2014

7/10/2014 20 18 22 6.5 6 3 8/10/2014 12835.06238 45134 Methane starts to return to pre-shifted trend

8/10/2014

9/10/2014 23 15 20 6 6 2 14/10/2014 24349.73006 31981 Sample taken after fill, insulation installed.

10/10/2014

11/10/2014

12/10/2014

13/10/2014 23 17 20 6.5 18 7 4 Not yet analysed, Mike Hatch unavailable.

14/10/2014

15/10/2014

16/10/2014 15 18 20 6 16 6.5 2 Not yet analysed, Mike Hatch unavailable.

17/10/2014

18/10/2014

19/10/2014

20/10/2014

21/10/2014 39 27 36 7 27 6 4 Not yet analysed, Mike Hatch unavailable.

22/10/2014

Tank 1 Tank #2