Development of a Zero Liquid Discharge Approach for ...faculty.ait.ac.th/visu/public/uploads/images/pdf/2014/chimeng.pdf · Development of a Zero Liquid Discharge Approach for Cooling

i

Development of a Zero Liquid Discharge Approach for Cooling Tower

Blowdown in Petrochemical Industry

by

Mov Chimeng

A thesis submitted in partial fulfillment of the requirements for the

degree of Master of Engineering in

Environmental Engineering and Management

Examination Committee: Prof. Chettiyappan Visvanathan (Chairperson)

Prof. Ajit P. Annachhatre

Dr. Thammarat Koottatep

Nationality:

Previous Degree:

Cambodian

Bachelor of Engineering in Rural Engineering (Water

Resources Engineering)

Institute of Technology of Cambodia, Cambodia

`

Scholarship Donor: AIT Fellowship

Asian Institute of Technology

School of Environment, Resources and Development

Thailand

May 2014

ii

Acknowledgements

It is my great pleasure to express my thoughtful and sincere gratitude to people who assisted,

supported and involved to make this research work possible.

Firstly, I would like to express my deepest appreciation to my advisor and also my

chairperson, Prof. C. Visvanathan, who always challenges me and provides me endless

supports, guidance, directions and priceless advices during entire thesis study.

Besides, it is my honor to thankfully appreciate my examination committee members, Prof.

Ajit P. Annachhatre and Dr. Thammarat Koottatep for their precious comments and valuable

suggestions since my proposal exam until the end of my thesis.

Secondly, I would like to express my sincere appreciation to Mr. Prapan Ariyamethee,

Gerneral Manager of Liquid Purification Engineering International (LPE) Co. Ltd.,

Nonthaburi, Thailand, and Mr. Phatthara Prudthisuntorn, Thai Polyacetal Co., Ltd. (TPAC),

Rayong, Thailand, who provided me the worthwhile opportunity to run my pilot scale

experiment in LPE, and to sample and audit wastewater in cooling tower blowdown

treatment plant in TPAC as well. Moreover, I am delighted to extend my thankful to all

LPE’s staffs who had involved and helped me during my time staying in LPE.

Another special thank goes to Prof. C. Visvanathan’s research staffs such Mr. Paul Jacob,

and Mr.Thusitha Rathnayake for their technical supports, kind encouragement, and useful

suggestions.

Moreover, many thanks would be extended to my team member in Prof. C. Visvanathan’s

research team like Ter, Ben, Plat, Kevin, Pik, Park, Milk, and Ellis, for their helpful

discussion and suggestions, generous supports and great friendship which is an unforgettable

moment. Not only these people who I would like to say thank you, but some other friends in

EEM program of August 2012 batch as well.

Apart from that, without 48 credits of tuition fee from AIT fellowship, I would not be able

to be here as well. Thus, I am really thankful to AIT for awarding me such a turning point

opportunity.

Finally, I would like to gratitude to my parents, sisters, and my relatives for their moral

support, financial support, endless inspiration, and encouragement in my entire period in

AIT. I can be success as today is a huge contribution from them.

iii

Abstract

Cooling system is considered as an important unit operation in any Petrochemical industries

where large portion of water is used to cool down heat from polymerization and

monomerization processes. Meanwhile, to keep consistent performance, some portion of

cooling tower blowdown (CTBD), full of TDS, silica and hardness, is periodically

withdrawn. However, this water is recovered for reuse in cooling tower by CTBD treatment

plan using UF and RO, but huge amount of concentrate of UF and RO system are still finally

discharged.

Therefore, in first phase of this study, water auditing was conducted to understand the

performance of CTBD treatment plant in Petrochemical Industry. The audit results indicated

that there was no significant operation problem in the plant since difference of input and

output was less than 30%. Around 180 m3/day of UF and RO concentrate were discharged

without any further recovery process. Pilot scale of Zero Liquid Discharge (ZLD) system

was used in this study to recover discharge. ZLD system was designed with two stage of RO

system which equipped with different type of pretreatment system, Ceramic MF for first

stage RO, Chemical precipitation (hardness and silica) with Duraflow MF for second stage

RO. Referring to experimental result, up to 85% of water could be recovered back to cooling

tower, while only less than 4% was rejected from second stage RO which consisted high

strength of TDS, hardness and silica. In addition, concentrate of ceramic MF and Duraflow

MF, full of suspended solids, was less than 9% combined together.

Proposed ZLD system was designed with 360 m3/day of designed flow and 80% water

recovery. From this proposed system, investment cost and O&M cost of system were

estimated where ceramic MF dominated 50% of total cost and Chemical precipitation with

Duraflow MF occupied more than 55% of O&M cost as well. Moreover, treatment cost was

calculated around 40 baht/m3 which was 10 baht/m3 more expensive than current water price

in TPAC (30 baht/m3). Hence, proposed ZLD system might be not very attractive from

industry’s point of view. Nevertheless, the future discharge regulations and policies, water

shortage condition, and corporate social responsibility issues could be the main driving force

for industry to accept ZLD system. Moreover, further study on pretreatment system like

ceramic membrane and chemical precipitation must bring down substantial amount of

investment and O&M cost as well. At the end of the day, ZLD system will gradually be

attracted by industrial for water reuse and recovery in industrial sector.

iv

Table of Contents

Chapter Title Page

Title Page i

Acknowledgements ii

Abstract iii

Table of Contents iv

List of Tables vi

List of Figures vii

List of Abbreviations ix

1 Introduction 1

1.1 Background 1

1.2 Objectives of the Study 2

1.3 Scope of the Study 3

2 Literature Review 4

2.1 Introduction 4

2.2 Type of Cooling System 4

2.3 Cooling Tower 5

2.4 Zero Liquid Discharge Approach (ZLD) 8

2.5 ZLD Application 12

2.6 Membrane Processes 19

2.7 Chemical Softening 29

2.8 Cost and Operating Consideration of ZLD System 34

2.9 Research Gaps of ZLD 35

3 Methodology 37

3.1 Introduction 37

3.2 Study Area 38

3.3 Water Auditing 40

3.4 Feed Water 41

3.5 System Component 42

3.6 Experimental Set-up 46

3.7 Operational Condition 46

3.8 Analytical Parameters and Methods 49

3.9 Engineering Design and Cost Information 49

3.10 Performance Evaluation and Criteria of System Design 50

4 Results and Discussions 54

4.1 Water Auditing 54

4.2 ZLD Pilot Scale Experiment 61

4.3 System Engineering Design 72

4.4 Cost Information 75

v

5 Conclusions and Recommendations 76

5.1 Conclusion 76

5.2 Recommendation for Further Research 77

References 79

Appendix A 83

Appendix B 88

Appendix C 99

Appendix D 115

Appendix E 122

vi

List of Tables

Table Title Page

2.1 Different Type of Cooling System Comparison 5 2.2 Typical Characteristic of CTBD 7 2.3 Treatment Technologies and Type of Discharge of Blowdown from Power Plant

using Reclaimed Water in US 8 2.4 Water Recovery of ZLD vs. Technologies 12

2.5 Companies and Their Product for ZLD 13 2.6 ZLD Technology Cost Comparison 13 2.7 Performance of MF and RO System of CTBD Recycle Plant 14

2.8 System Capital Cost Estimation of CTBD Recycle 15 2.9 Operating Cost Estimation of CTBD Recycle 15 2.10 Performance of MF and RO System of Steel Plating Mill 16 2.11 System Capital Cost Estimation of Steel Plating Mill 17

2.12 Operating Cost Estimation of Steel Plating Mill 17 2.13 System Capital Cost Estimation of RO Brine Recovery Process 18 2.14 Operating Cost Estimation of RO Brine Recovery Process 18 2.15 Comparison of Dead-end and Cross Flow Filtration 21

2.16 Properties of Current Good-quality Commercial Membrane 23 2.17 Parameters Influencing RO/NF Performance 27

2.18 Fouling Reduction Techniques and Its Description 28

2.19 Basic MF Chemical Pre-treatment Applied for Different Industrial WW 29

2.20 Classification of Lime Softening with Hardness Residual 30 2.21 Summary of Previous Research of ZLD 36

3.1 Feed Water Characteristic 41 3.2 Specification of Ceramic Membrane 42 3.3 Specification of Duraflow Membrane 44

3.4 Specification of Hydranautics CPA2-4040 44 3.5 Function of Other Sub-equipment of System 45

3.6 Operational Condition of ZLD System 46

3.7 Operational Scenario of ZLD System 48 3.8 Major Equipment for Cost Information 49

3.9 Analytical Parameters and Method 53 4.1 Accumulative Water Volume and Running Hour of UF and RO Plant 55

4.2 Characteristic of Water Samples of CTBD Treatment Plant 57 4.3 Summary of Input and Output of CTBD Treatment Plant 59 4.4 Feed Water Characteristic 61

4.5 Result of RO-1 Experiment with Optimum Pressure 64 4.6 Result of Chemical Precipitation Optimization 65

4.7 Operation Data of Both Cases at 2 bar Feed Pressure 67 4.8 Before and After Neutralized of Duraflow Permeate 69 4.9 Result of RO-2 Experiment with Optimum Pressure 71

4.10 Final Permeate Characteristic 72

4.11 Cost Information of Major System 75

vii

List of Figures

Figure Title Page

2.1 Once-through (a), cooling tower (b), dry cooling (c), and hybrid cooling (d) 4 2.2 Cooling tower process 6 2.3 Zero liquid discharge system 10 2.4 Thermal brine concentrator 10 2.5 Non thermal brine concentrator (NTBC) 11

2.6 Spray dryer schematic 11 2.7 Evaporation pond in Great Salt Lake, UT, USA 12 2.8 Effect of salinity and composition on ZLD cost 13

2.9 Flow diagram of CTBD recycle 14 2.10 Process diagram of steel plating mill wastewater recycling 16 2.11 Process diagram of RO brine recovery 18 2.12 Schematic representation of a two-phase system separated by a membrane 19

2.13 Comparison of membrane technology separation 20 2.14 Different membrane sizes and typical separations possible 20 2.15 Dead-end filtration 21 2.16 Cross-flow filtration 21

2.17 Performance vs. feed water salinity 24 2.18 Performance vs. feed Pressure 25

2.19 Performance vs. feed water temperature 25

2.20 Performance vs. permeate recovery ratio 26

2.21 Effect of temperature on silica removal 32 2.22 Effect of retention time on silica removal 32

2.23 Residual silica vs. concentration of MgO at 60oC 33 2.24 Cost estimating levels and accuracy 34 3.1 Overall study plan 37

3.2 Location of Thai Polyacetal Co., Ltd 38 3.3 Process diagram of TPAC 38

3.4 TPAC’s Lupital (Acetal Copolymer) 39

3.5 Usage of cooling tower in petrochemical industry 39 3.6 Cooling tower in TPAC 40

3.7 Process of CTBD treatment plant 40 3.8 Duraflow DF-401 44

3.9 Hydranautics CPA2-4040 45 3.10 Experimental set-up of ZLD system 52 4.1 Flow diagram of CTBD treatment plant in TPAC 54

4.2 Overall information of flow rate and TDS of CTBD treatment plant 58 4.3 Water balance 59

4.4 Salt balance 60 4.5 Flow rate and salt content of each water stream 60 4.6 Flux and TMP of ceramic membrane 62

4.7 Rejection rate and flux with different feed pressure 63

4.8 Flux and TMP of RO-1 at 8 bar feed pressure 63

4.9 Result of total hardness and silica residual of bench test 65 4.10 Silica reduction with MgO added 66 4.11 Flux comparison for both cases 67 4.12 Permeate result of both cases 68 4.13 Flux and TMP of Duraflow MF 69

viii

4.14 Flux and rejection of different feed pressure 70

4.15 Flux and TMP of second stage RO at 12 bar 70 4.16 Percentage of RO permeate and other rejections 71 4.17 Overall system design 73

4.18 Salt balance of proposed ZLD system 73 4.19 Plan diagram of proposed ZLD system 74

ix

List of Abbreviations

ACF : Activated Carbone Filter

ACFa : Average Concentration Factor

BDL : Below Detection Limit

BW : Backwash

CEB : Chemical Enhance Backwash

CETP : Common Effluent Treatment Plant

CIP : Chemical in Place

CLS : Cold Lime Softening

CMD : Cubic Meter per Day

Conc : Concentrate

CTBD : Cooling Tower Blow Down

F : Flux

GE : General Electric Company

GPM : Gallon per Minute

HERO : High Efficiency Reverse Osmosis

HEVAP : High Efficiency Evaporation

HLS : Hot Lime Softening

LMH : Liter per Square Meter per Hour

LPE : Liquid Purification Engineering International Co., LTD

LPH : Liter per Hour

MCWO : Molecular Weight Cut Off

MF : Microfiltration

MGD : Million Gallon per Day

MVC : Mechanical Vapor Compression

NF : Nanofiltration

NTBC : Non Thermal Brine Concentrator

O&M : Operation and Maintenance

Per : Permeate

PLC : Programme Logic Controller

PPM : Part Per Million

PSI : Pound per Square Inch

PVDF : Polyvinylidene Fluoride

RO : Reverse Osmosis

SADG : Steam Assisted Gravity Drainage

SDI : Silt Density Index

TDS : Total Dissolved Solids

Temp : Temperature

THB : Thai Baht

TMP : Trans-membrane Pressure

TPAC : Thai Polyacetal Co., Ltd.

TSS : Total Suspended Solids

UF : Ultrafiltration

USD : US Dollar

WHO : World Health Organization

WLS : Warm Lime Softening

WSSC : Washington Suburban Sanitary Commission

WWTP : Wastewater Treatment Plant

ZLD : Zero Liquid Discharge

1

Chapter 1

Introduction

1.1 Background

According to United Nations Environment Programme (UNEP), the volume of freshwater

resources is around 35 million km3, or about 2.5 percent of the total volume on earth, about

1.4 billion km3. Moreover, almost about 24 million km3 or 70 percent of these fresh water

resources is in the form of ice, and snow cover in mountainous region, the Antarctic and

Arctic region. Only round 30 percent of worlds freshwater is stored as groundwater, soil

moisture, swamp, lakes, rivers, and atmosphere that is potentially available for human use.

However, less than 1 percent of all freshwater resources, about 200,000 km3, is the total

usable freshwater supply for humans and ecosystem. (UN-Water, 2013)

However, due to increasing of world population from day to day, over-consuming water

resources, climate change, and pollution, available fresh water for people become lesser and

lesser. Almost every continent and more than 40 percent of the people on our world are

already affected by water scarcity. By 2025, 1.8 billion people will be living in countries or

regions with complete water scarcity, and more than half of the world’s population could be

living under water stressed situations. (UN-Water, 2013)

Nowadays, in order to save our water sources, reclamation and reuse of wastewater from

municipalities and industries have been more and more widespread. Water scarcity in

regions lack of fresh water, saving fresh water resource and money, meeting the stringent

effluent standard, technologies development and cost improvement, etc. are the key factors

for the increase in the use of membrane technology.

Petrochemical industry, textile, pulp and paper, power plant, and palm oil industries are the

suitable applicants in reclaiming and reusing wastewater. Large portion of wastewater are

discharging every day from those industries’ processes. For example, in petrochemical

industry, large amount of water are utilized in cooling system for various process such as

polymerization and monomerization process (distillation process). Hot water from these

process is sent to cooling tower to cool down.

Moreover, cooling tower is the highest water usage process which is used in many industries,

especially in petrochemical industry. It is a heat removal device used to transfer process

water’s heat to the atmosphere. Large portion of water is lost due to evaporation, drift, and

blowdown. Significant amount of feed water is added to keep the water balance and the

steady-state of cooling water operation. Due to the evaporation of water in cooling system,

the dissolved solids present in makeup water become more and more concentrated. At some

points, the dissolved solids concentration exceed the solubility limit which results in

precipitation and formation of undesirable scale. To avoid and control this problem, some

amount of water need to be drained out of cooling tower which is termed cooling tower

blowdown (CTBD), contains high strength of total dissolve solid and hardness (Ca2+, Mg2+,

etc.).

Presently, industries are reclaiming and reusing CTBD by using differences type of treatment

process to desalt and remove the constituents. Combination of conventional techniques (bio-

chemical treatment) and ion-exchange technology, Microfiltration (MF) and Ultrafiltration

2

(UF), Reverse osmosis (RO) and nanofiltration (NF), etc. have been used. The treated CTBD

is recycled and reused in boiler, process water, or makeup water. Furthermore, a portion of

blowdown, the reject stream from RO or NF, is further sent to brine concentrators (use

thermal energy to evaporate water, and condense and discharge as clean distilled water) and

crystallizer. There is no liquid discharge out of the plant, only sludge and salt cake is

produced, and is sent to landfill. This concept is known as Zero Liquid Discharge (ZLD)

(Drake et al., 2013).

To remove TDS from water, there are many alternative treatment process like: Deionization,

distillation, and Membrane (RO, NF, MF, and NF). Deionization or ion-exchange

technology is a filter process used in water reclamation application whereby TDS are

removed from water through ion exchange, but significant space requirement, long treatment

time, regeneration of resin, high running cost (electricity need), etc. are the major drawback

of the technology (Zhang et al., 2007). The same thing with distillation process, high energy

consumption input to evaporate the feed water, carryover of volatile constituents found in

treated reclaimed water, scaling due to inorganic salt, and corrosion are the typical issues

and also the limitation of this process that need further to control (Asano et al., 2007).

In recent years, the use of membranes filtration like MF, UF, NF and RO in industrial sector

has been developed significantly, especially in treating CTBD. Zhang et al. (2007) reported

that MF or UF is generally selected as pretreatment in RO or NF plant after chemical

addition, coagulation, and gravity settling since MF and UF effectively remove particles

colloids, bacteria and virus. According to Asano et al. (2007), if we compare between MF

and UF with conventional filtration, there are many reasons why MF and UF is nominated

such as: low treatment chemical, small footprint requirement, low labor requirement,

bacteria and virus removal, etc. Moreover, NF and RO require hydrostatic pressure to

overcome osmotic pressure of the feed stream, and are able to remove particles of size less

than 0.01 µm, for example, aqueous salt, organic matter, pesticides, and herbicides. RO has

been used in many applications, particularly in CTBD, for removal of TDS up to 95 to 99.5%

and 95 to 97% for dissolved organic matter. Furthermore, NF is much similar as RO; the

differences are lower pressure require, lower removal of monovalent ions, and looser than

RO (Asano et al., 2007).

1.2 Objectives of the Study

The main objective of this study was to reclaim and concentrate large amount of wastewater

from cooling tower blowdown treatment plant which was discharging high total dissolved

solid of wastewater from industry, Zero Liquid discharge (ZLD).The specific objectives to

achieve this are:

To conduct a water audit in Petrochemical industry’s cooling tower blowdown

treatment plant.

To develop a membrane base pilot scale experiment for water recovery by using real

wastewater from cooling tower blowdown treatment plant.

To design an engineering membrane based system of Zero Liquid Discharge

approach and to provide cost information.

3

1.3 Scope of the Study

For this study, the scope was limited and shown as following:

Water auditing was scoped and focused only on water and salt balance of CTBD

treatment plant.

For ZLD approach, only membrane based system was focused on. The other

processes like dewatering processes, evaporator or crystallizer were excluded.

The pilot experiment and samples analysis were conducted in Liquid Purification

Engineering Company (LPE).

The system was designed in consideration both engineering feasibility and financial

viability.

4

Chapter 2

Literature Review

2.1 Introduction

In every petrochemical industry, cooling system are one of the major units. It plays as a heat

exchanger and cooling down their product. Cooling system of petrochemical industry is

normally used in polymerize and monomerize processes which are the distillation processes.

Waste heat from these processes is adsorbed and cooled in cooling system of the plant, then

cooled water once again go back to system to adsorb the heat from product. Due to

evaporation and drift of cooling system, some portion of water which contained high TDS

and chloride concentration need to be drained and replaced with make-up water.

2.2 Type of Cooling System

Cooling system is characterized into three main type: once-trough cooling, cooling tower or

wet cooling, and dry cooling (Figure 2.1). Besides, there is also a hybrid version between

wet and dry. Presently, dry or hybrid wet and dry cooling are less popular than once-through

cooling and cooling tower. The water requirement of each type of system are different, and

contribute an enormous effect on the overall water consumption (Delgado & Herzog, 2012).

Table 2.1 indicates the comparison of each type of cooling system.

Figure 2.1 Once-through (a), cooling tower (b), dry cooling (c), and hybrid cooling (d)

(GAO, 2009)

(c)

5

Table 2.1 Different Type of Cooling System Comparison

Type of

system Once through Cooling tower Dry cooling Hybrid cooling

Description of

system

Withdraw water

from surface

water and

discharge warm

water

(wastewater)

directly to

environment

Water is sent to

condenser to

remove the heat,

lower

temperature

water returned to

condenser.

No water is used.

Only ambient air is

used to cool down

the steam by fan

blowing. Steam is

condensed as

liquid water

Combination of

cooling and dry

system. It can

operate both wet

and dry to

increase the

efficiency.

Advantages

Simplest

system

Low

investment

cost

Closed-loop

system

high heat

transfer

No water

consumption

High efficiency

Reduce water

and power usage

Small footprint

Drawbacks

Affect aquatic

life and

ecosystem

Corrosion

Scale or other

deposition

Biological

fouling

Costly

TDS increase

due to

evaporation

Corrosion and

deposition due

to high

temperature

and TDS

Long retention

time

High cost

Low efficiency

Very high cost

Water

withdraw Large Medium No Medium

Water

consumption* Low Large No Large

Note: *: water lose due to evaporation and drift

2.3 Cooling Tower

Cooling tower is a heat removal device, which extracts waste heat to the atmosphere though

the cooling of a water stream to a lower temperature. Common applications for cooling

towers are providing cooled water for air-conditioning, manufacturing and electric power

generation.

Cool water in cooling tower basin is brought to condenser to cool down or condense the

exhaust heat from system, and hot water from condenser will go back to cooling tower where

water is cooled. Hot water is distributed or sprayed from the top of tower as a small droplet.

Air from atmosphere, sometimes air from air blower, is flowed in the opposite direction of

sprayed water. The heat of droplet is removed and cooled down to atmospheric temperature.

Cooled water goes back to cooling tower basin once again. Figure 2.2 gives a nice

demonstration of how cooling tower work to remove the heat.

Because evaporation consists of pure water, the concentration of dissolved minerals and

other solids in circulating water will increase unless some means of dissolved-solids control,

6

such as blow-down, is provided. Some water is also lost by droplets being carried out with

the exhaust air (drift) ("Cooling Technology Institute," 2013).

Figure 2.2 Cooling tower process

2.3.1 Cooling Tower Blowdown and its characteristic

Cooling tower operation includes periodic discharge or continuous discharge of concentrated

recirculating water in order to maintain desired cycles of concentration and control the

accumulation of total dissolved solids (TDS) in the system resulting from continuous inflow

of TDS with makeup water and evaporative losses in the system (Figure 2.2). This periodic

discharge or continuous discharge of recirculating water is called blowdown and it contains

high levels of TDS as well as chemicals that are typically added to the system to control

corrosion, scaling and bio fouling. Due to fairly low water quality, blowdown is typically

subjected to some level of treatment in order to meet effluent standard that are ruled by the

final disposal options (Feng, 2008). However, many situations, people just discharge CTBD

directly to environment or common effluent treatment plant (CETP) without any recycle

back to process.

The characteristic of CTBD is varied from plant to plant depending on cycle of

concentration, 4 to 6 times are typical (Lander, 2013). Following table is the typical

parameters of concern from CTBD.

7

Table 2.2 Typical Characteristic of CTBD

Parameter Units Values Parameter Units Values

pH - 8.5 Sodium mg/L 1,158

Conductivity µS/cm 7,132 Potassium mg/L 52

Sulfate mg/L 2,341 TSS mg/L >200

Chloride mg/L 399 TDS mg/L 2,500-4,500

COD mg/L 200-500 Calcium mg CaCO3/L 300-800

Silica mg/L 50-150 Magnesium mg CaCO3/L 200-500

Source: Lander (2013) and Yu et al. (2013)

2.3.2 Cooling Tower Blowdown Management Option

Feng (2010) mentioned that management options available for cooling tower blowdown

typically depend on its water quality, local discharge regulations and capabilities of

treatment processes under consideration. Typical options for cooling tower blowdown

management include:

Discharge to surface waters

Depending on regulation of local area and blowdown characteristic, CTBD is discharge

directly to surface water which is the main option of once-through cooling system (Figure

2.6a). However, the assimilative capacity of receiving water to handle the blowdown is

limited and the quality of blowdown has to meet criteria that address the regulatory

requirements for public health and environmental protection, especially assimilative

capacity of receiving water.

Discharge to wastewater treatment plant (WWTPs)

Blowdown discharge to a local wastewater treatment plant (WWTP) may be an attractive

and economical option if accepted by the WWTP. Nevertheless, the acceptance may be

depending on chemicals present in the blowdown, and will reduces the load on power plants

but increases the demand on local WWTPs. The size and treatment options are the two main

factors that determine whether a WWTP can accept the cooling tower blowdown from a

thermoelectric power plant.

Zero liquid discharge (ZLD)

This alternative involves extensive treatment of blowdown to facilitate its reuse combined

with some form of volume reduction to minimize or eliminate the need for liquid discharge.

This option become more and more popular since it is an environmental friendly technology

and economized technology. As seen in Table 2.3, most power plants using wastewater for

cooling would choose this option where the concentrated solids are the only waste leaving

the plant.

8

Table 2.3 Treatment Technologies and Type of Discharge of Blowdown from Power

Plant using Reclaimed Water in US

Plant Name State Type of

Discharge Treatment Technologies

Magnolia California ZLD

Lime-soda softening, media

filtration, RO, evaporator,

evaporation pond

Emery Lowa WWTP -

Panda

Brandywine Maryland WWTP -

Jones Station Texas ZLD, irrigation Evaporation pond

San Juan New Mexico ZLD Evaporator, evaporation pond, RO

Linden New Jersey WWTP -

Nixon Colorado ZLD RO, evaporator

MVPP California WWTP, recycle RO

Palo Verde Arizona ZLD Evaporation pond

Walnut Creek

Energy Park California WWTP -

Note: ZLD: Zero liquid discharge

WWTP: Discharge to wastewater treatment plant or sanitary sewer system

Source: Feng (2008)

2.4 Zero Liquid Discharge Approach (ZLD)

Zero Liquid Discharge (ZLD) describes a process that completely eliminates liquid

discharge from a system. The goal of any well-designed ZLD system is to minimize the

volume of wastewater that requires treatment, process wastewater in an economically

feasible manner, while clean steam is also produce which suitable for reuse elsewhere in the

process. ZLD is also a process which benefits for both industry and municipal organization

as well as environment (Visvanathan, 2013).

ZLD typically includes one or more of the following advanced treatment technologies:

Pretreatment, Membrane process, and Evaporator/crystallizer.

2.4.1 Advantages and disadvantages of ZLD

ZLD becomes more and more widespread of application nowadays and future due to some

advantages and drivers of ZLD itself. Many points which can be seen as advantages of ZLD

are listed as following:

Reduce water usage

Concentrates on eliminating water discharge

Purify and recycle plant wastewater

Changing liquid waste into disposable dry solid waste

Delivering effluent water into plant process stream to be reused

Can incorporate many different unit operations to eliminate water discharge

Can deliver valuable financial returns where water conservation and strict permitting

regulation have significantly increased the cost of industrial use.

9

However, the only one drawback of ZLD is capital cost on system and electricity which

developers or designers are trying hard to bring down capital cost to make ZLD perfect

technology for industrial sector.

2.4.2 Driving force of ZLD

Water scarcity, social responsibility, economic, and regulation are the main drivers of ZLD

system (Visvanathan, 2013).

Water Scarcity:

Water is a resource which is getting scarce in many geographic condition like in many

location in US, the Middle East, Africa, India, and China. Those places the amount of water

is less than 5% of wastewater is presently recovered. Due to that issue, water recovery and

recycle are completely necessary.

Social Responsibility:

Reuse and recycling of wastewater is a kind of social responsibility which could bring good

image for industry. Not only image, but it also will directly or indirectly boost their

reputation, and could reinforce company’s brand.

Economic:

When portable or tap water and cost of discharge wastewater are rising, industrial sector

should look at the potential saving by comparing the cost of ZLD with the cost of tap water

with discharging expense.

Regulation:

In some countries, regulation of wastewater discharge become more and more stringent that

need to speed more and more money in treating wastewater to meet the effluent regulation.

Therefore, it’s better to put ZLD to reuse it again since its quality might be better than tap

water after treatment.

2.4.3 ZLD technologies

ZLD System removes dissolved solids from the wastewater and returns distilled water to the

process (source). Reverse osmosis (membrane filtration) may be used to concentrate a

portion of the waste stream and return the clean permeate to the process. Moreover,

pretreatment of RO is one of the most important part of system to avoid RO’s scaling,

fouling, biological growth, and metal precipitation. In this case, a much smaller volume (the

reject) will require evaporation, thus enhancing performance and reducing power

consumption.

Figure 2.3 illustrates typically system of ZLD which includes one or more of the following

advanced treatment technologies: Pretreatment, Membrane filtration, Evaporator,

crystallizer, and solid recovery (filter press).

10

Figure 2.3 Zero liquid discharge system (Degrémont, 2013)

The most commonly technologies used in ZLD process consist of: RO membrane, brine

concentrator, evaporator/crystallizer, etc.

RO Membrane:

RO is designed to remove TDS in wastewater, and around 75-80% of water is able to recover

and reuse again in process. It usually uses in brine/seawater desalination application which

contains high concentration of TDS. In ZLD, concentrate of RO further go to

Evaporator/Crystallizer or brine concentrator.

Thermal brine concentrator:

Thermal energy are used to evaporate water, which is successively condensed and

discharged as clean distilled water. It is a kind of scientifically and environmentally friendly

technology (Figure 2.4). More than 95% of plant’s wastewater are recovered from brine

concentrator and crystallizer while the remaining brine is product or solid.

Figure 2.4 Thermal brine concentrator (GE, 2013)

Distillate/condensate

Concentrated brine Feed brine

11

Non thermal brine concentrator:

Reduce wastewater volume by 10 to 50 times and fresh water intake significantly by 10% to

20%. Moreover, due to minimization of waste chemical and energy consumption, it is

considered as environmental friendly process which helps industries easily meet

sustainability and public image goal (Figure 2.5).

Figure 2.5 Non thermal brine concentrator (NTBC) (GE, 2013)

Evaporator/Crystallizer:

Evaporator concentrates brines up to 250,000 ppm of TDS by using mechanical vapor

recompression. Then, the exceed 250,000 ppm of TDS from evaporator is pumped under

high pressure to a forced circulation where salt cake is formed and sent to landfill. Both

distillate from evaporator and crystallizer are returned to process.

Spray Dryers:

Liquid wastewater is turned to dry powder or particle by rapidly drying with hot gas (Figure

2.6). Spray dryers are commonly used in many thermally sensitive material like food

production and pharmaceutical production. It is an alternative technology for ZLD, but only

low volume of flows is applicable.

Figure 2.6 Spray dryer schematic

12

Evaporation Pond:

Wastewater is deposited in a large open ponds allowing water to evaporate through solar

radiation and wind, leaving a pond of concentrated residual waste for treatment (Figure 2.7).

It is a useful way in ZLD since there is no effluent is discharged into environment. However,

odor generation, large space requirement, and seasonal variation (raining season) are the

main drawback for it presently.

Figure 2.7 Evaporation pond in Great Salt Lake, UT, USA

ZLD is the most effective technology nowadays in recovering of wastewater. More than 99%

of water is reclaimed from wastewater which the highest water recovery rate comparing to

RO, ED, or NTBC, according to GE, 2013. Table 2.4 presents the comparison water recovery

between ZLD and various technology.

Table 2.4 Water Recovery of ZLD vs. Technologies

Technology Water Recovery (%)

Reverse Osmosis 75%-80%

Electro dialysis 80%-85%

High efficiency RO (HERO) 85%-90%

Non thermal brine concentrator (NTBC) 93%-96%

ZLD 99+%

Source: GE (2013)

2.5 ZLD Application

2.5.1 Companies involved in ZLD

Presently, more and more companies are brought the attention in working with membrane

especially in ZLD technology. All those companies have been producing and developing

new membranes and technologies to make ZLD become more and more efficient in term of

economic and technical feasibility. Degrémont, Duraflow, ENCON, Siemens, and GE

Company are among the top companies in working and manufacturing product of ZLD

technology. Some are working on membranes like MF pre-treatment for RO, or RO, while

some are focusing on evaporator and crystallizer, and some companies are developing whole

ZLD system. Table 2.5 indicates companies involve in ZLD and their products.

13

Table 2.5 Companies and Their Product for ZLD

Company Technology Product Reference

Duraflow RO pretreatment:

Tubular MF membrane

DF 401, DF 404, DF 406, DF 415, DF

419…

(Duraflow,

2013)

Degrémont ZLD and RO

pretreatment

Infilco ZLD system, ALTEONTM UF,

ECOSKID™ UF, SKID UF…

(Degrémont,

2013)

ENCON Evaporator/Crystallizer

Mechanical Vapor Compression

(MVC) evaporator, Thermal

evaporator, drum dryer…

(ENCON,

2013)

Aquatech ZLD, RO system, and

Evaporator

High Efficiency RO (HERO), High

Efficiency Evaporation (HEVAP)…

(Aquatech,

2011)

GE ZLD,

Evaporator/Crystallizer

AquaSel, Steam assisted gravity

drainage (SAGD), Non thermal

brine concentrator (NTBC)…

(GE, 2013)

2.5.2 Cost effective

According to Visvanathan (2013), both concentration of salinity and composition on

individual process have significant effect on: unit capital costs, operating costs, and

annualized costs as well (Figure 2.8).

Effect of Salinity

concentration

Composition

Equipment sizeCapital costs and

operating cost as well

Effect on Effect on

Figure 2.8 Effect of salinity and composition on ZLD cost

Moreover, Visvanathan (2013) added that in ZLD the reduction of waste volume prior to

brine concentrator or crystallizer application is always cost effective. Typically, treatment

process with evaporator and crystallizer system of ZLD is relatively very expensive that the

process without evaporator and crystallizer process. For example, 80% of wastewater can be

recovered and reused by the process without evaporator and crystallizer, and the rest 20%

can be further recovered by evaporator and crystallizer. However, the cost of evaporator and

crystallizer for the last 20% capturing could double the cost of 80% wastewater recovery

without evaporator and crystallizer system.

Table 2.6 below are some of cost comparison in ZLD technology.

Table 2.6 ZLD Technology Cost Comparison

ZLD Technology Cost Effective

Without evaporator and crystallizer system Less expensive

with evaporator and crystallizer system More expensive

Without a second stage RO More expensive

With lime softening and second stage RO Less expensive

14

ZLD Technology Cost Effective

Non thermal evaporation equipment Low cost

Large evaporation ponds High unit capital cost

Two stage of RO Less expensive

Only one stage of RO More expensive

Source: Visvanathan (2013)

2.5.3 Case studies

Case 01: Cooling Tower Blowdown (CTBD) recycle

Project Detail: This case study is located in power plant in California and Nevada, USA,

which was installed in 2003. It was the application of 100% cooling tower blowdown

(CTBD) recycle from power plant. Lime softening, MF filtration, RO, and

evaporator/crystallizer were all the important technologies which is applied. With MF and

RO, more than 80% of wastewater was recovered. The whole process diagram of this study

is shown in Figure 2.9.

Figure 2.9 Flow diagram of CTBD recycle (Lander, 2013)

Plant performance: The performance of MF and RO system is demonstrated in Table

2.7.

Table 2.7 Performance of MF and RO System of CTBD Recycle Plant

Parameter Unit CTBD MF Filtrate RO permeate

Turbidity NTU - <1 -

pH - 8.5 10 7.5

TDS mg/L 1,200-1,400 1,600 <50

Mg Hardness mg/L as CaCO3 150 <10 <0.5

: Lander (2013) presented during ZLD Training Program in LPE, 12 November 2013

15

Parameter Unit CTBD MF Filtrate RO permeate

Calcium Hardness mg/L as CaCO3 360 <20 <1

COD mg/L 400 <100 <5

Silica mg/L as SiO2 150 <10 <1

SDI - - <3 -

Cost estimation: System capital cost and operation cost (Table 2.8 and 2.9) was

estimated with system flow of 50 m3/h, 850 LMH of MF flux, 25 LMH of brackish RO flux,

17 LMH of seawater RO flux, and 7.5 m3/h of evaporator rate. The system was operated 24

hours per day and 7 days per week. However, labor cost were not included in this estimation.

Table 2.8 System Capital Cost Estimation of CTBD Recycle

Components Cost ($ USD)

2 stages chemical pre treatment

(30 minutes retention time) $ 180,000

Microfiltration (72 modules, 2 skids) $ 530,000

Brackish water RO (70% recovery)

15 m3/h brine produced $ 300,000

Seawater RO (50% recovery)

7.5 m3/h brine produced $ 150,000

Evaporator (7.5 m3/h) $ 1,150,000

Total $ 2,210,000

Source: Lander (2013)

Table 2.9 Operating Cost Estimation of CTBD Recycle

Contributors Cost ($ USD/10 m3)

Chemical treatment (lime, sodium carbonate and ferric salt) $ 3.3

MF electricity $ 1.48

MF sludge disposal (Hauling and land filling) $ 2.51

MF membrane replacement $ 0.66

RO (chemicals, electricity, and membrane replacement) $ 6.08

Total $ 14.03


Benefit of CTBD recycle:

Significant enhancement in power production cost from heat transfer efficiency

improvement with high-quality makeup water.

Lower overall operation cost in cooling tower in treatment chemicals, maintenance

labor, and water makeup.

The maximum daily water supply allowable is meet due to decreasing of water

consumption.

Cut down wastewater volume to meet the maximum daily limitation of wastewater

discharge.

16

Case 02: Wastewater Recycle at a Steel Plating Mill

Project detail: 100 m3/h of wastewater from steel plating mill which contains high metals

like Nickel and Zinc was designed to be recycle. Metal precipitation, MF, and RO were the

main processes which were applied. Moreover, powder activated carbon was used after MF

to remove organic compound. The process diagram is presented in Figure 2.10. The main

objectives were not only wastewater recycle, but also to improve wastewater treatment

reliability, improve the quality of metal residuals, and discharge brine in compliance.

Figure 2.10 Process diagram of steel plating mill wastewater recycling (Lander, 2013)

Plant performance: The performance of MF and RO system is demonstrated in Table

2.10.

Table 2.10 Performance of MF and RO System of Steel Plating Mill

Parameter Unit Influent MF Filtrate RO Brine RO Permeate

Conductivity µS/Cm 3000-4000 3500-4500 12000-18000 40-80

Oil and grease mg/L 5 Bdl Bdl Bdl

TDS mg/L 1800-2400 2200-3000 5900-11000 22-45

Hardness mg/L as

CaCO3 50-100 25-50 100-200 Bdl

TSS mg/L 291 <1 <10 Bdl

Copper mg/L 0.26 Bdl 0.01 Bdl

Lead mg/L 0.49 Bdl Bdl Bdl

Nickel mg/L 119 Bdl Bdl Bdl

Zinc mg/L 78 Bdl Bdl Bdl

Cost estimation: With the system flow of 50 m3/h, 850 LMH of MF flux, and 25 LMH

of brackish RO flux, system capital cost and operation cost (Table 2.11 and 2.12) was

estimated. The system was operated 24 hours per day and 7 days per week. However, labor

cost were not included in this estimation.

17

Table 2.11 System Capital Cost Estimation of Steel Plating Mill




Microfiltration (96modules, 2 skids) $ 800,000



Total $ 1,600,000


Table 2.12 Operating Cost Estimation of Steel Plating Mill


Chemical treatment (caustic, metal precipitant,

coagulant, powder activated carbon) $ 5.68




RO (chemicals, electricity, and membrane

replacement) $ 6.08

Total $ 17.34


Benefit of steel plating mill wastewater recycle:

More than 80% of the mill industrial wastewater is recycle.

Concentration of metal are reliably and comfortably below discharge limit even in

RO brine as shown in Table 2.10.

Due to cleaner water, plating rinse rate have been reduced (reducing the hydraulic

load on wastewater treatment.

Improved reliability has reduced management stress.

Case 03: RO Brine Recovery Process in Tire Manufacturer

Project detail: In tire manufacturer, product water was produced from well water by

using RO. RO brine was mixed with CTBD and production wastewater, and further treat

with second stage RO and crystallizer. Therefore, 100% of wastewater in the industry were

recovery. Figure 2.11 demonstrates the simplified process flow diagram of RO brine

recovery in tire manufacturer.

18

Figure 2.11 Process diagram of RO brine recovery (Lander, 2013)

Plant performance: For MF, filtrate quality was less than 100 mg/L of total hardness, 5-

7 mg/L of silica, less than 1 NTU of turbidity, and less that 3 of SDI. TDS concentration of

RO permeate was less than 150 mg/L, while salt rejection recovery rate were 98-99% and

more than 80% respectively.

Cost estimation: With the system flow of 50 m3/h, 850 LMH of MF flux, 25 LMH of

brackish RO flux, and 5 m3/h of crystallizer rate, system capital cost and operation cost

(Table 2.13 and 2.14) was estimated. The system was operated 24 hours per day and 7 days

per week. However, labor cost were not included in this estimation.

Table 2.13 System Capital Cost Estimation of RO Brine Recovery Process




Microfiltration (36modules, 1 skids) $ 300,000



Crystallizer (feed rate 5 m3/h) $800,000

Total $ 1,330,000


Table 2.14 Operating Cost Estimation of RO Brine Recovery Process


Chemical treatment (caustic, metal precipitant, coagulant,

powder activated carbon) $ 1.98




RO (chemicals, electricity, and membrane replacement) $ 7.93

Total $ 13.64


19

Benefit of RO brine recovery process in tire manufacturer:

It is cost effective by using single step tubular MF to replace conventional treatment

such as clarifier, multimedia filtration, and carbon filter.

High water recovery of RO brine (>80%) due to high filtrate quality from MF

process, turbidity <1 NTU and SDI <3.

Harmful chemical components in brine solution were completely removed by MF

which is a safeguard of RO from adverse fouling.

2.6 Membrane Processes

Membrane technology is an emerging technology and due to its multidisciplinary character

it can be used in a large number of separation process. At the moment, membrane

technologies are used in a wide range of applications and many such of the application are

growing significantly. From the economic point of view, the present membrane technologies

are intermediate between the development of first generation membrane process which

consists microfiltration (MF), ultrafiltration (NF), nanofiltration (NF), reverse osmosis

(RO), electrodialysis (ED), membrane electrolysis (ME), diffusion dialysis (DD), and

dialysis; and the second-generation membrane processes like: gas separation (GS),

membrane contractor (MC), vapor permeation (VP), membrane distillation (MD),

pervaporation (PV), and carrier mediated process (Mulder, 1996).

The separation is achieved because the membrane has ability to transport one component

from feed mixture more readily than other due to differences in physical and/or chemical

properties between the membrane and the permeating components.

Figure 2.12 Schematic representation of a two-phase system separated by a

membrane (Mulder, 1996)

There are four different types of membranes according to the pore size and the molecular

weight of the solute it can reject. However, it is not easy at all to classify them since there

are no absolute criteria that divide those four membrane types.

Membrane

Driving force

ΔC, ΔP, ΔT, ΔE

Phase 2 Phase 1

Feed side Permeate side

20

Figure 2.13 Comparison of membrane technology separation (Visvanathan, 2013)

Figure 2.13 and 2.14 illustrate classification of membrane filtration as a function of

molecular weight cut off and pore size. UF and MF are basically similar in that the mode of

separation in molecular sieving through increasingly fine pores. MF filter colloidal particles

and bacteria from 0.1 to 10µm in diameter. UF can be used to filter dissolved

macromolecules, such as proteins, from solutions. The mechanism of separation by NF and

RO is quite different. In fact, NF and RO can be considered as being intermediate between

open porous types of membrane (MF/UF) and dense nonporous membranes

(pervaporation/gas separation). NF is the preferred process in removing of lower

concentrations, di or multivalent ions and microsolutes with molecular weights ranging from

500 to a few thousand Dalton. On the other hand, RO is suitable for removing monovalent

ions (Na-, Cl, etc.) and high retention of NaCl is required with high feed concentrations.

Figure 2.14 Different membrane sizes and typical separations possible

In membrane filtration, there are two main vital mode of operation, illustrated in Figure 2.5

and 2.6, which are dead-end mode or in-line mode, and cross-flow mode or tangential mode.

Dead-end filtration: When using a dead-end filtration technique, all the fluid passes through

the membrane and all particles larger than the pore sizes of the membrane are stopped at its

surface. Particle size prevents contaminants from entering and passing through the

21

membrane. This means that the trapped particles start to build up a "filter cake" on the surface

of the membrane which reduces the efficiency of the filtration process until the filter cake is

washed away in back flushing.

Figure 2.15 Dead-end filtration (Baker, 2004)

Cross-flow filtration: In cross flow filtration, the fluid feed stream runs tangential to the

membrane, establishing a pressure differential across the membrane. This causes some of

the particles to pass through the membrane. Remaining particles continue to flow across the

membrane, "cleaning it". In contrast to the dead-end filtration technique, the use of a

tangential flow will prevent thicker particles from building up a "filter cake".

Figure 2.16 Cross-flow filtration (Baker, 2004)

Comparison of advantages and disadvantages of dead-end and cross-flow MF can be shown

as following Table 2.15.

Table 2.15 Comparison of Dead-end and Cross Flow Filtration

Dead-end Cross flow

Low capital cost

High operating cost since membrane

must be replaced after each use and

disposal can be problem

Operation is simple—no moving parts

Best suited to dilute (low solid

content) solution. Membrane

replacement costs increase with

particle concentrations in the feed

solution

Representative application: sterile

filtration, clarification/sterilization of

beer and wine

High capital cost

Operating costs modest as membrane

have extended lifetimes if regularly

cleaned

Operating is complex—filers require

regular cleaning

Best suited to high solid content

solutions. Costs are relatively

independent of feed solution particle

concentrations

Representative application:

continuous culture / cell recycle,

filtration of oilfield produced water

22

2.6.1 Microfiltration

MF is the process of filtration with a micrometer sized filter. The filters can be in a

submerged configuration or a pressure vessel configuration. They can be hollow fibers, flat

sheet, tubular, spiral wound, hollow fine fiber or track etched. These filters are porous and

allow water, monovalent species (Na+, Cl-), dissolved organic matter, small colloids and

viruses through but do not allow particles, sediment, algae or large bacteria through.

MF systems are designed to remove suspended solids down to 0.1 μm in size, in a feed

solution with up to 2-3 % in concentration. It is very suitable for use in place of traditional

clarifiers or as a pre-filter to a water recycling/recover reverse osmosis system. Typically,

these membranes have pore sizes in the range of 0.1 to 10 μm.

In MF, usually the most widely used process design is dead-end or in-line filtration, in which

the entire fluid flow is forced through the membrane under pressure (Figure 2.20). As

particles accumulate on the membrane surface or in its interior, the pressure required to

maintain the required flow increases, until at some point the membrane must be replaced.

Potential application of MF: Sterile Filtration of Pharmaceuticals, Sterilization of wine

and beer, Electronics industry, Drinking water treatment, etc.

2.6.2 Ultrafiltration

UF is a form of filtration which uses membranes with smaller pores (0.01 to 0.1 μm). These

membrane systems are used under high pressures to push the permeate through the

membrane. The membranes are described in terms of MWCO (molecular weight cut off),

and particles smaller than the MWCO of a membrane passes through the membrane while

the larger particles are retained by the membrane.

A key factor determining the performance of ultrafiltration membranes is concentration

polarization, which causes membrane fouling due to deposition of retained colloidal and

macromolecular material on the membrane surface. To overcome this fouling problem,

several cleaning methods are used to remove the densified gel layer of retained material from

membrane surface. In order to maintain the performance of all UF, regular cleaning is

required. A typical cleaning cycle is as follows:

1. Flush the system several times with hot water at the highest possible circulation rate.

2. Treat the system with an appropriate acid or alkali wash, depending on the nature of

the layer.

3. Treat the system with a hot detergent solution.

4. Flush the system thoroughly with water to remove all traces of detergent; mea-sure

the pure water flux through the membrane modules under standard test conditions.

Even after cleaning, some degree of permanent flux loss over time is expected. If the

restoration of flux is less than expected, repeat steps 1–3.

Potential application of UF: Electrocoat paint, Food Industry (Cheese production), Food

Industry (Clarification of fruit juice), Oil-water emulsion, Process water and product

recycling, Biotechnology (concentration and removal of products from fermentation

operations used in enzyme production, cell harvesting, or virus production), etc.

23

2.6.3 Nanofiltration and Reverse Osmosis

NF membranes and RO membranes are used to remove trace organic molecules and ions in

water filtration. Due to the looser skin layer structure, NF membranes tend to pass

monovalent ions (Li+, Na+, K+, etc.), but not di and trivalent ions (Ca2+, Mg2+, Fe2+, Fe3+,

etc.). Typical rejection efficiency of mono- and divalent ions by NF is 30-80% and 70-95%,

respectively. RO membranes reject monovalent ions at 90-99.9% while rejection divalent

ions at higher efficiency. It is noteworthy that NF and RO are not solely rely on the size

exclusion mechanism, but also rely on the solution-diffusion mechanism that essentially

affected by how easily the solutes can dissolve in the membrane material. Since low-

molecular-weight charge-neutral solvents, such as methanol, ethanol, acetone, etc., easily

dissolve into polyamide, rejection efficiency of such solvents tends to be low, e.g. 10-50%

(Mulder, 1996).

RO can be grouped into three main categories:

Seawater and brackish water desalination membranes operated with 0.5 to 5 wt. %

salt solutions at pressures of 14–69 bar.

Low-pressure NF membranes operated with 200–5000 ppm salt solutions at

pressures of 7–14 bar.

Hyperfiltration membranes used to separate solutes from organic solvent solutions.

The comparative performance of high-pressure, high-rejection reverse osmosis membranes,

medium-pressure brackish water desalting membranes, and low-pressure nanofiltration

membranes is shown in Table 2.16.

Table 2.16 Properties of Current Good-quality Commercial Membrane

Parameter Seawater membrane

(SW-30)

Brackish water

membrane (CA)

NF membrane

(NTR-7250)

Pressure (bar) 55-69 20-34 7-10

Solution

concentration (%) 1-5 0.2-0.5 0.05

Rejection (%)

NaCl

MgCl

MgSO2

Na2SO4

NaNo3

Ethylene glycol

Glycerol

Ethanol

Sucrose

99.5

99.9

99.9

99.8

90

70

96

--

100

97

99

99.9

99.1

90

--

--

20

99.9

60

89

99

99

45

--

--

20

99

Source: Baker (2004)

Referring to Baker (2004), NF usually have high rejections to most dissolved organic solutes

with molecular weights above 100 to 200 and good salt rejection at salt concentrations below

1000 to 2000 ppm salt. The membranes are also two to five fold more permeable than

brackish and sea water reverse osmosis membranes, so they can be operated at pressures as

low as 3 to 10 bar and still produce useful flux. For these reasons, their principal application

has been in the removal of low levels of contaminants from already relatively clean water.

24

Potential application of RO/NF: Brackish water desalination, Seawater desalination,

Ultrapure water production, Wastewater treatment, Drinking water treatment, Organic

solvent separation, CTBD treatment, ZLD process, etc.

2.6.4 Parameters affecting performance of RO/NF

The main performance parameters of a reverse osmosis or a nanofiltration process are

permeate flux and salt rejection. Normally, the performance of a membrane system are

mainly affected by variable parameters including (Hydranautics, 2013):

Feed water salt concentration (salinity of feed water)

Feed pressure

Feed water temperature

Permeate recovery ratio

Membrane compaction and fouling.

Feed water salinity:

The fluctuation of feed water concentration during RO/NF operation might be due to

seasonal change of feed water salinity, or due to irregular operation of a number of water

sources with different salinity. As shown in Figure 2.17, the effect of increasing of feed

water salinity could result in declining of both permeate flux and salt rejection. Moreover, if

the changing of feed water contains a higher soluble salinity (salt) than in the design feed

water, water recovery ratio need to be decreased to avoid any scaling possibility from

concentrate stream.

Figure 2.17 Performance vs. feed water salinity (Dow, 2013)

Feed Pressure:

With the increasing of effective feed pressure, the permeate salinity will decrease while the

permeate flux and salt rejection will increase (Figure 2.18). In the operating, feed pressure

is adjusted to compensate for fluctuation of feed water temperature, salinity, and permeate

flux declined due to fouling, age of membrane, or compaction of membrane to keep a

constant flux rate.

25

Figure 2.18 Performance vs. feed Pressure (Dow, 2013)

Feed water temperature:

When all other parameters are kept constant and temperature increases, the permeate flux

and salt passage (permeate salinity) will increase (Figure 2.19). It is due to the changing in

rate of diffusion through membrane, and the changing in permeate flux with temperature is

defined by the following equation:

1 1exp

273 298TCF K

t

Equation 2.1

Where: TCF : Temperature correction factor (dimensionless)

K : Membrane-specific manufacturer-supplied constant (1/K)

K=2700 for hydranautic membrane

t : Operating temperature (oC)

In this equation, 25oC of temperature with TCF=1 is used as a reference point.

Figure 2.19 Performance vs. feed water temperature (Dow, 2013)

Permeate recovery ratio:

The ratio of permeate flow to feed flow is known as recovery ratio. According to Figure

2.20, permeate flux and salt rejection will drop gradually to sharply with the increasing of

26

recovery ratio. Permeate flux could decrease until zero if concentration of salt reaches a

value where osmotic pressure of concentrate is as high as applied feed pressure. Furthermore,

the average of feed salinity could calculate from feed salinity by multiply with average

concentration factor (ACF). Then, osmotic pressure of feed could be calculated. Equation

for calculation o average concentration factor (ACF) is shown below:

1ln( ) /

1ACF R

R

Equation 2.2

Where ACF : Average concentration factor (dimensionless)

R : Recovery ration

Figure 2.20 Performance vs. permeate recovery ratio (Dow, 2013)

Membrane compaction and fouling:

Membrane compaction is caused by the increasing in membrane density which is resulted

from exposure of membrane to high pressure of feed water. Rate of diffusion of water and

TDS through membrane will be decreased which causes flux declined. To retain a constant

flux rate, higher and higher pressure has to be applied (Hydranautics, 2013).

Deposition of impurity (organic and inorganic substances) on membrane surface and/or

blockage of feed channels which could result in non-reversible membrane degradation is

called membrane fouling. Membrane fouling somehow ends up with increasing of pressure

drop, flux declined, membrane degradation, or even complete destruction of membrane

elements (Hydranautics, 2013).

The below Table 2.17 demonstrates a summary of the impact influencing RO/NF’s

performance.

27

Table 2.17 Parameters Influencing RO/NF Performance

Increasing of Permeate Flux Salt Passage

Feed water salinity Decrease Increase

Feed pressure Increase Decrease

Feed water temperature Increase Increase

Permeate recovery ratio Decrease Increase

Source: Dow (2013)

2.6.5 Membrane fouling management

RO membranes are design for removal of dissolved solids, but harmfully affected or fouled

by suspended solids, colloidal material, bacteria or scale. The common examples of such

foulants are calcium precipitates, metal oxides, colloidal silica coating, and organics. Most

of the time, most of these fouling substance are found in industrial wastewater. Decrease in

flux and salt rejection, an increase in feed pressure and energy consumption and often

irreversible membrane damage, are the influence of membrane fouling (Chan, 2011).

Chan (2011) added that once membrane is fouled, only mild cleaning chemicals including

citric acid and detergent can be used. Sulfuric acid, hydrochloric acid, bleach, and peroxide,

which are stronger or more effective cleaning chemicals, could cause harmful damages to

the RO membrane.

In wastewater recycling applications, RO can hardly function on its own without any

protection from the fouling materials. Appropriate pretreatment must be provided to achieve

stable performance of RO membranes (Duraflow, 2013).

Microfiltration (MF) Pre-treatment

MF has given the ability to considerably decrease membrane fouling and provide stable,

expectable RO performance. According to Chan (2011), the achievement of MF for this

application can be described to the following key reasons:

MF membrane is designed to remove suspended solids and colloidal particles (RO

foulants). Some of the MF products can handle very high TSS of >5000 mg/L in the

influent.

MF membrane could be made of a variety of polymeric materials, including PVDF,

which has strong resistance to concentrated chemicals. Thus, various kind of

persistent fouling elements, both organic and inorganic which are difficult to be

remove by mild chemical cleaning, can be cleaned and removed with mineral acids,

oxidizers (bleach, peroxide), caustic and selected organic solvents.

The quality of MF product, NTU (<1.0) and SDI (<3.0), is able to meet the feed

water criteria specified by all RO manufacturers.

The conversion of chemical or physical characteristic of the foulants in the

wastewater into particles, chemical precipitation, is easy for MF to remove all those

foulants.

Besides, regulated contaminants in the raw water also could be removed by MF to

make the RO reject more manageable for recovery or discharge downstream.

28

Several fouling reduction or flux enhancement techniques are combined into the design of

MF products. Most commercial MF products utilize one or more of the techniques shown

below. In order to select a proper MF products, it is very vital in understanding these features

(Duraflow, 2013).

Table 2.18 Fouling Reduction Techniques and Its Description

Fouling Reduction

Technique Description

Backwash

Periodic reversal of filtrate into the flow channels. Cleaning

chemicals are added into the filtrate backwash to improve the

cleaning effectiveness.

Turbulence Promotion

Use of insertion (baffles, wire rings, etc.) or moving sponge

balls to promote turbulence to break down the boundary layer

adjacent to the membrane surfaces.

Polarization

Minimization

Operate at high feed velocity and low trans-membrane pressure

(TMP) to minimize polarization and compaction, respectively.

Surface Modification Modify membrane charge and/or hydrophilic/hydrophobic

property of the membrane to fit specific foulants.

Pore Size Modification Vary membrane pore size to fit specific foulant size.

Chemical Pre-

treatment

Change the chemical and physical characteristic of foulants to

mitigate the fouling effect on the selected membrane.

Source: Duraflow (2013)

The chemical pre-treatment technique could offer an extensive range of flexibility to

counterpart the others while most of the above techniques can solve only one or two specific

types of fouling contaminants (Table 2.19). For example, particle size of foulants can be

manipulated through addition of appropriate chemicals to satisfy the pore size and surface

charge of the selected membrane.

MF Chemical Pre-treatment

Because of changing in the characteristics of the foulants, chemical pre-treatment lessens the

effects of the fouling components on membrane. In the design phase, the following principles

must be met to achieve minimum fouling (Duraflow, 2013):

All settable fouling components must be converted to the solid form with particle

size greater than the membrane pores. To meet this objective, interfering chemicals

such as organic compounds are typically destroyed or destabilized.

Un-settable dissolved fouling composition must be removed via adsorption or

chemically changed to membrane compatible forms.

The treatment chemicals used must be chemically compatible with the membrane

and with each other.

If pass through the MF, the chemicals used must be compatible with the RO

membrane.

29

Table 2.19 Basic MF Chemical Pre-treatment Applied for Different Industrial WW

Fouling

Elements Industries / Source MF Pre-treatment Chemistry

Hardness

(Ca & Mg)

Power Generation

CTBD Chemical softening - Lime & soda ash

Heavy Metals

Automotive

Metal Finishing

Metal Refinery

Steel/Iron

Hydroxide precipitation – Caustic/lime

Sulfide precipitation – Sodium sulfide

Organo-sulfur precipitation – Sodium

Dithiocarbamate

Fluoride Semiconductor De-fluoridation – Calcium/aluminum salts

Sulfate Mining

Concrete Sulfate precipitation - lime and aluminum

salt.

Silica Groundwater Chemical adsorption – Magnesium salt

Oil & Grease Petrochemical

Industrial Laundry

Adsorption – Lime / activated carbon

Acid Cracking – Sulfuric acid

Organic All Industries

Adsorption – Lime / activated carbon

Coagulation – Aluminum/iron salts

Oxidation destruction – Bleach /Peroxide

Source: Lander and Chan (2012)

2.7 Chemical Softening

2.7.1 Hardness removal

Chemical softening or lime softening is one of the most widely used process in soften water.

This process is used to reduce mainly hardness, calcium and magnesium, from water by

using chemicals. Lime (calcium hydroxide, Ca(OH)2) and soda ash (sodium carbonate,

Na2CO3) are commonly used to chemicals which cause carbonate hardness and non-

carbonate hardness respectively. Hardness causing ions or mineral form into particles or

almost insoluble particles, when lime and soda ash are added into water, and ready to

precipitate.

According to Al-Mutaz and Al-Anezi (2004), lime softening reactions can be summarized

by the following categories:

a. Carbon dioxide removal: This reaction is completed at pH=8.3

CO2 + Ca(OH)2 CaCO3 + H2O Equation 2.3

b. Carbonate hardness removal: By adding lime (Ca(OH)2), Calcium and magnesium

bicarbonate which cause carbonate are precipitated as calcium carbonate and

magnesium hydroxide. At pH of 9.4-9.5, magnesium bicarbonate is converted to

magnesium carbonate which is soluble. pH is raised to 10.6-11 by adding excess lime

to precipitate it as magnesium hydroxide.

Ca(HCO3)2 + Ca(OH)2 2CaCO3 +2H2O Equation 2.4

Mg(HCO3)2 + Ca(OH)2 CaCO3 + MgCO3 + 2H2O Equation 2.5

MgCO3 + Ca(OH)2 CaCO3 + Mg(OH)2 Equation 2.6

30

c. Calcium non-carbonate hardness removal: Calcium sulfate and calcium chloride,

cause calcium non-carbonate hardness, are precipitated as calcium carbonate by

adding soda ash, Na2CO3.

CaSO4 + Na2CO3 CaCO3 + Na2SO4 Equation 2.7

CaCl2 + Na2CO3 CaCO3 + 2NaCl Equation 2.8

d. Magnesium non-carbonate hardness: Magnesium non-carbonate hardness,

magnesium sulfate and magnesium chloride, are precipitated as magnesium

hydroxide by the addition of lime (Ca(OH)2). However, this reaction produce

calcium non-carbonate hardness where soda ash need to be added to precipitate it as

calcium carbonate.

MgCl2 + Ca(OH)2 Mg(OH)2 + CaCl2 Equation 2.9

CaCl2 + Na2CO3 CaCO3 + 2NaCl Equation 2.10

MgSO4 + Ca(OH)2 Mg(OH)2 + CaSO4 Equation 2.11

CaSO4 + Na2CO3 CaCO3 Na2SO4 Equation 2.12

As an old rule of thumb, lime softening is only applicable method for hardness higher than

100-150 mg/L as CaCO3 and flowrates larger than 200m3/h (Toghraei, 2012). He also added

that there are three main type of lime softening system: Cold Lime Softening (CLS), Warm

Lime Softening (WLS), and Hot Lime Softening (HLS). The classification is according to

operating temperature of the system which is shown in Table 2.19.

Table 2.20 Classification of Lime Softening with Hardness Residual

Lime softener type Operating Temperature (oC) Residual Hardness (mg/L)

Cold lime Softening 15-60 80-110

Warm lime Softening 60-85 30-50

Hot lime Softening 90-105 15-25

2.7.2 Chemical dosage

Lime (Ca(OH)2)

(A+B+C+D) + % ExcessLime(mg/L)=

Purity of lime as a decimal Equation 2.13

Where,

A = Carbon Dioxide in source water = mg/L CO2 x (Ca(OH)2/ CO2)

= mg/L CO2 x 74/44 = mg/L CO2 x 1.68

B = Bicarbonate alkalinity = mg/L CaCO3 x (Ca(OH)2/ CaCO3)

= mg/L CaCO3 x 74/100 = mg/L CaCO3 x 0.74

C = Hydroxide alkalinity = mg/L CaCO3 x (Ca(OH)2/ CaCO3)

= mg/L CaCO3 x 74/100 = mg/L CaCO3 x 0.74

: Retrieved from Mountain Empire Community College (MECC), November 16, 2013.

31

D = Magnesium = mg/L Mg2+ x (Ca(OH)2/ Mg(OH)2)

= mg/L Mg2+ x 74/24.3 = mg/L Mg2+ x 3.05

Soda Ash (Na2CO3)

2 3

3

Na COSoda Ash mg/L = Non-Carbonate Hardness ×

CaCO Equation 2.14

So,

Soda Ash (mg/L) = mg/L Non-Carbonate Hardness as CaCO3 x Na2CO3/CaCO3

= mg/L Non-Carbonate Hardness as CaCO3 x 106/100

= mg/L Non-Carbonate Hardness as CaCO3 x 1.06

Magnesium Salt (MgO)

MM

ggO

OMg required Mg. Hardness

M (m /L =

gg )

Equation 2.15

Where,

Mg required (mg/L Mg2+) = mg/L SiO2 x 2

Mg Hardness (mg/L Mg2+) = mg/L CaCO3 x 24.3/100

2.7.3 Silica removal in lime softening

During lime softening process, calcium and magnesium are precipitated and deposited as

calcium carbonate and magnesium hydroxide. Due to the larger floc formation of magnesium

hydroxide, silica particles in water are able to be adsorbed or entrapped. As the result, silica

will be removed with the precipitation of magnesium hydroxide by adsorption in lime

softening (Al-Mutaz & Al-Anezi, 2004). The mechanism of silica adsorbs with magnesium

hydroxide is shown in following reaction (Shand, 2006):

Na2SiO3 + Mg(OH)2 + H2O MgSiO3 . H2O Equation 2.11

The optimum pH for silica adsorption onto magnesium oxide is around 10–11, which

coincides nicely with the conditions created during lime softening. Soluble silica can also be

removed by magnesium bicarbonate as the following reaction (Al-Mutaz & Al-Anezi, 2002).

Mg(HCO3) + 2H4SiO4 MgSi3O6(OH)2 + 6H2O + 2CO2 Equation 2.12

Shand (2006) reported that in silica removal process, magnesium compounds such as

magnesium sulfate, dolomitic lime, calcined magnesite, magnesium carbonate or

magnesium oxide are normally used. However, because of high removal efficiency and no

contribution to increase solid content of water, magnesium oxide is commonly employed.

Moreover, he also pointed out some important factors which effect on silica removal

efficiency such as temperature, pH, retention time, and sludge recirculation. Temperature

has a great effect on removal efficiency of silica, and higher temperature the greater removal

(Figure 2.21).

32

Figure 2.21 Effect of temperature on silica removal (Shand, 2006)

Moreover, retention time is also a significant parameter effect on silica removal. As shown

in Figure 2.22, silica removal is nearly complete in 15 minutes of retention at temperature

95oC, but at temperature 23oC the removal of silica gradually increases (Shand, 2006). More

retention, MgO could react and precipitate more. That is the reason why silica will remove

more and more too.

Figure 2.22 Effect of retention time on silica removal (Shand, 2006)

Partially recirculation of sludge, reacted magnesium oxide, into new coming raw water

which contain high silica concentration could get a significant reduction of silica content.

Shand (2006) mentioned that up to 60% magnesium requirements is reduced when sludge

recirculation is used. According to lime softening, hot and warm lime softening have a better

removal of hardness (calcium and magnesium). Increasing in temperature, it is a catalyst of

33

chemical reaction which magnesium could react more rapidly. Once magnesium precipitate

more and more, silica will also significant reduce due to adsorption.

Suciu and Miller (1980) had stated in the report about “Silica Removal from Raft River

Geothermal Water” that magnesium oxide (MgO) are the most effective chemical in silica

removal compare to MgCl2, MgSO4, and Mg(HCO3)2. In that case study, source of water

was from Raft River where the water was discharged from a 5 MW Pilot Power Plant. Water

source was rich of silica content and calcium hardness, 180 ppm as SiO2 and 93.9 ppm as

CaCO3 respectively. Figure 2.23 illustrates clearly about the silica residual concentration

versus the concentration of magnesium oxide added. At pH of 11.2, residual silica in water

is decreased considerably and more effective than that of pH of 10.2. However, the graph

turned almost stable from 80 ppm to 160 ppm of MgO added. It shows that even more and

more MgO is added, the silica residual still keep constant or slightly decrease.

Figure 2.23 Residual silica vs. concentration of MgO at 60oC (Suciu & Miller, 1980)

34

2.8 Cost and Operating Consideration of ZLD System

2.8.1 Cost consideration

In ZLD system, cost is the most important factor. Typically, ZLD’s cost is quite costly

compared to discharge-based system which need to be focused on cost optimization

(Mickley, 2008). Referring to Mickley (2008), several consideration factors are involved in

selection of an optimum system cost as following:

- Economical versus cheap: Cheap products always reduce the cost of system, but

it’s very important to make sure that these product does not reflect to low efficiency

of system and a reduction in quality of system.

- Design Constringency and reliability: Cost can be reduced by selection equipment

only to meet design condition. However, this concept results in lower-cost for first

period, but it does very little to support long-term projects (integrity, reliability and

redundancy).

- Simple versus complex: Brine evaporator is commonly use to achieve ZLD

approach. However, a simple big size of evaporator is very costly. There are most of

the times membrane system, iron exchange and chemical precipitation/treatment

process help to concentrate the volume of wastewater and also volume of evaporator.

As a result, significant amount of cost could be saved, but a complex system need to

be designed.

- Total cost: Each option must be estimated thoroughly before comparing options.

Annual operating costs which comprise energy consumption, labor, chemicals,

maintenance, etc. and capital cost are also included in total cost.

Montgomery (1985) reported that cost estimation is normally required several levels and

percentage of accuracy of project, as shown in Figure 2.24. He added that 2 types of

estimation are prepared in the design stage of a project. Cost estimates used in comparing

and evaluating process alternatives is the first type, and need sufficient detail and accuracy

of total construction and operation and maintenance cost. The second type is detailed

estimate of construction cost which is utilized to compare and evaluate bids received for the

construction of the project.

Project and Estimating

phases

Level of Accuracy

Expected

Project pre-planning

----------

Feasibility estimates

± 45%

Project planning

----------

Preliminary estimates

± 30%

Project design

----------

Alternative evaluation

Relative value

± 10%

Absolute value

inconsequential

Project construction

----------

Bid evaluation

± 7%

Figure 2.24 Cost estimating levels and accuracy (Montgomery, 1985)

35

2.8.2 Operating consideration

In all of membrane system especially ZLD system, automation running of whole system is

main attractive tool. Nonetheless, an overall controlled person is still needed to manage

operation. This person responsibility is to look after or check system operation, chemicals,

and equipment weekly, monthly, or even yearly in the plant. Furthermore, at least once a

month or every two months, this person should conduct an thorough check of important

operating parameters to make sure that plant’s goal and parameter are being met (Mickley,

2008).

In the review of plant, the following questions should be posed by controlled person

(Mickley, 2008) :

- Does system operate according to design?

- Does system utilize water correctly, and is it optimized?

- Are there enough and correct type of chemical additive of system?

- Do all of equipment function well?

2.9 Research Gaps of ZLD

ZLD actually is an emerge technology, and it’s not very attractive by industry due to its main

disadvantage, capital cost. Recently, many researches have conducted in order to improve

both performance and capital cost to make it more and more application. As example, Sajid

Hussain (2012) conducted a ZLD research in Textile Dyeing Effluents at Tirupur, India.

Meanwhile, Lander (2013) and Drake et al. (2013) also did many researches on the

application of ZLD in Power Plant Industry, Steel Plating Mill, and RO Brine Recovery in

United States of America. Besides, those researches have conducted in various industries

and countries, but not in Petrochemical industries and Thailand. Table 2.21 is the summary

of some previous case study of ZLD.

Therefore, this research study was conducted to fulfill the gaps from previous researchers.

Petrochemical industry could become a very classic and new case study of ZLD approach

which is conducted in Rayong, Thailand.

36

Table 2.21 Summary of Previous Research of ZLD

Researcher

Names

Application

/Industry Location Applied Technology

Capacity

(m3/h) Benefit /Performance

Sajid

Hussain

(2012)

Textile

dyeing

Tirupur,

India

Pretreatment

(biological oxidation)

RO system

Evaporator

/Crystallizer

53

Recycling >98% of

the water.

Reuse of > 90% of the

salt.

Cleaning of the local

environment

Lander

(2013)

Power

plant’s

CTBD

recovery

California

and

Nevada,

USA

Cold lime softening

MF and RO system

Filter press

Evaporator

/Crystallizer

56

Total water recycle

100%

Reduce wastewater

volume

Lander

(2013)

RO brine

recovery USA

Lime-soda softening

2 stages RO system

Filter press

Evaporator

/Crystallizer

100

Complete removal of

detrimental chemical

components in the

brine solution.

Cost-effective single-

step tubular filtration

process

100% water recovery

Lander

(2013)

Steel Plating

Mill USA

Metal precipitation

MF and RO system 100

80% water recovery

Better quality water

from the RO

Improved reliability

Aquatech

(2003)

Power

plant’s

CTBD

California,

USA

Lime-soda softening

HERO system

Belt filter

Evaporator

/Crystallizer

90

Significant reduce in

Power Consumption

Footprint saving

100% water recovery

Seigworth et

al. (1995) Power plant

Virginia,

USA

Pressure filter

EDR and RO

Evaporator

/Crystallizer

57

Recovery high

distilled water

Energy and cost

reduction by reduce

the size of evaporator

by using EDR and RO

37

Chapter 3

Methodology

3.1 Introduction

This pilot scale study of ZLD system was conducted at Liquid Purification Engineering

International, Co., LTD (LPE), Nonthaburi, Thailand. The system was operated in batch

mode. Water and salt balance of CTBD treatment plant in TPAC was the first main part of

this study in order to evaluate the performance of the plant. Moreover, system were divided

into two stages of RO system with different pretreatment process of each stage. In first stage

RO, ceramic membrane was used to remove suspended solid and turbidity to meet

compliance RO feed water criteria. Also, the concentrate of first stage RO went to the second

stage RO. Chemical precipitation and Duraflow (MF) played an important role as

pretreatment of second stage where hardness and silica were reduced. Optimum dosage of

chemical precipitation enhance the removal efficiency of Duraflow (MF). In both stages RO,

TDS and other ionic compound were reduced. Samples were taken at feed, concentrate, and

permeate side of ceramic, Duraflow and both RO, and were analyzed in LPE’s laboratory.

The Figure 3.1 illustrate the overall study plant of this research.

Figure 3.1 Overall study plan

38

3.2 Study Area

3.2.1 Location

The experimental study was conducted at Liquid Purification Engineering (LPE)

International Co., LTD. and Thai Polyacetal Co., Ltd. (TPAC). Besides, the real wastewater

was collected from CTBD treatment plant in TPAC itself to run the experiment in LPE.

Thai Polyacetal Co., Ltd. (TPAC) is located in Padaeng Industrial Estate, 1/1 Padaeng Rd.,

Map-Ta-Phut, Rayong 21150, Thailand, around 204 km from AIT, and around 178 km from

Bangkok.

Figure 3.2 Location of Thai Polyacetal Co., Ltd

3.2.2 Company production

Production quality control system is considered an excellent system. Computer and cutting-

edge technology are used under the highly qualified person’s management in each step of

production line. The processes are control from raw material’s quality checking to the

product outcomes, finished product, and delivery system (TPAC-TPCC, 2007). Production

line of TPAC is presented in Figure 3.3.

Methanol

Formaldenyde

Trioxane

Polymerization

Lupital

Catalyst Comonomer

Figure 3.3 Process diagram of TPAC

AIT

TPAC

39

The main product of TPAC is Lupital, Acetal Copolymer (Figure 3.4), which can produce

some other plastics product like children toy, knife handle, helmet, fan impeller, etc (Figure

A.1, Appendix A).

Figure 3.4 TPAC’s Lupital (Acetal Copolymer)

3.2.3 Cooling tower used in petrochemical industry

In TPAC, cooling tower is used in cooling system to cool down and remove the heat from

all monomer and polymerization processes (Figure 3.5). Around 1,320-1,400 m3/d (55-

58m3/h) of make-up water is used every day in cooling tower, and large amount of blowdown

water from need to be removed to keep concentration stable in cooling tower. Moreover, hot

water, temperature 41-43oC, around 4,000m3/h is brought to cool in cooling tower.

Figure 3.5 Usage of cooling tower in petrochemical industry

40

Figure 3.6 Cooling tower in TPAC

All such a large amount of blowdown water from cooling tower is treated in UF and RO

plant and reuse again. The treatment is using UF as pretreatment of RO and follow by RO

to remove TDS and other ionic compound. Figure 3.7 below is the flow diagram of CTBD

treatment plant in TPAC.

Figure 3.7 Process of CTBD treatment plant

3.3 Water Auditing

Water auditing in this study focused only on water and salt balance which was done by field

survey and data collection to see the performance of CTBD’s treatment plant. CTBD’s

treatment plant was receiving CTBD water from cooling tower around 500 to 600 m3/day.

UF and RO plant were the most important unit operation for water auditing. Flow rate,

accumulative volume of water, and filtration hour (running hour) of input and out of all unit

operations were recorded. Additionally, feed water, concentrate water, permeate water,

backwash and CEB water of UF and RO system were sampled and analyzed its characteristic

in LPE’s laboratory.

41

- % 1

00%

OutputAccuracy

Inp

In t

ut

pu Equation 3.1

If the percentage of accuracy is less than 30% (Different between input and output), there is

no problem in running system. In contrast, it might be some losing or problems in the plant

which need further investigation (Visvanathan, 2004).

According to field survey and observation, it shown that large amount of water were

discharging every day from drain pit, around 180 m3/day. The losing of large portion of

wastewater was the main driving force for ZLD system to reclaim and recycle back to

process.

3.4 Feed Water

Feed water of this ZLD system was taken from the drain pit of CTBD treatment plant of

TPAC, where RO reject, RO flush, UF backwash, and UF CEB were discharged. The quality

of water was rich of hardness and silica which are the major foulant of RO. The characteristic

of feed water is shown in Table 3.1.

Table 3.1 Feed Water Characteristic

Parameter Unit Method Reference Method Feed Water

Appearance - Observation APHA (2012), 2110 Slightly

Turbid

Turbidity NTU Nephelometric APHA (2012), 2130 (B) 1.7

pH (at 250C) - Electrometric APHA (2012), 4500-H (B) 7.9

Conductivity μS/cm Conductivity

meter APHA (2012), 2510 B 657

TDS mg/L Conductivity

meter APHA (2012), 2510 A 427

P- Alkalinity mg/L as CaCO3 Titration APHA (2012), 2320 (B) Nil

M-Alkalinity mg/L as CaCO3 Titration APHA (2012), 2320 (B) 115

Total Hardness mg/L as CaCO3 EDTA

Titrimetric APHA (2012), 2340 (C) 156.55

Calcium

Hardness mg/L as CaCO3

EDTA

Titrimetric APHA (2012), 3500-Ca (B) 109.2

Chloride mg/L as Cl- Aegentometric APHA (2012), 4500 Cl- (B) 86.85

Sulfate mg/L as SO4-2 Turbidimetric APHA (2012), 4500 -SO4-2 (E) 38.18

Silica mg/L as SiO2 Molybdosilicate APHA (2012), 4500 –SiO2 (C) 43.63

Free Chlorine mg/L as Cl2 Photometer - 0.01

From membrane fouling standpoint, an SDI < 5, is equivalent to a Turbidity < 1 NTU ("Silt Density Index

(SDI) Measurement & Testing," 2007)

42

3.5 System Component

The system comprised two stages of RO system which equipped with RO pretreatment

individually. Ceramic membrane was the pretreatment of first stages RO, and chemical

precipitation and Duraflow MF were the second stage RO’s pretreatment. Moreover, other

sub-units consisted pump (feed, circulation and high pressure pump), flow meter, pressure

gauge, pH and thermometer, and RO pre-filter. The system was operated in batch mode, and

all the data were recorded manually.

RO pretreatment

Pretreatment is the most important phase in water recycling and reuse with RO. It will protect

and mitigate RO membrane from fouling, scaling, or degradation by various organic,

mineral, and chemicals consist in wastewater. Hardness (Calcium and Magnesium), Silica,

Organic (Antiscalant & Dispersants) and total suspended solids (TSS) are the major RO

foulants. Ceramic membrane MF, Chemical treatment and Duraflow MF are the main

processes of RO pretreatment.

a. Ceramic membrane MF

Many cases, ceramic membrane is used as pretreatment of RO since it has high ability in

removing suspended solid to meet compliance with RO feed water criteria.

CMF2-M-200 of tubular ceramic membrane model of 19 channels, which installed vertically

in stainless steel housing, was selected for the first stage RO’s pretreatment. Feed water was

fed from the top of membrane house through those 19 inner channels by one feed pump and

one circulate pump to increase cross-flow velocity. Permeate was collected outside of each

surface of membrane channels. The detail of membrane specification is given in Table 3.2.

Table 3.2 Specification of Ceramic Membrane

Parameter Specification

Membrane company name Jiangsu Jiuwu Hi-Tech Co., LTD

Membrane model CMF2-M-200-193110163.7-Z

Membrane type Microfiltration

Membrane material Ceramic (Al2O3/ZrO2)

Filtration mode Cross-flow (inside-outside)

Outside diameter 30 mm

Length 1016 mm

Channel number 19

Channel diameter 3.3 mm

Nominal pore size 0.2 μm

Porosity 36%

Effective surface area 0.22 m2

Maximum flux (250C, 1 bar) ≥600 LMH

pH range 1-14

43

b. Chemical Treatment

In chemical treatment most of foulants and contaminants like hardness, silica, and organic

compound were eliminated by using various chemicals. After added chemicals, the foulants

and contaminants were converted into or adsorbed onto insoluble particles which are easy to

precipitate and separate.

In this case, the concentrate from first stage RO contains high total hardness and silica which

are the major foulants of second stage RO. Therefore, soda ash and magnesium oxide were

added to precipitate hardness (Ca2+ and Mg2+) and silica (SiO2) respectively (Lander & Chan,

2012).

The optimum dosage of chemical was got from the bench test with the various chemical

variation. Soda ash, and magnesium oxide were added as coagulants. In order to vary those

dosages, initial calculation from water characteristic was done, and calculation formula is

shown as following:

Soda Ash (Na2CO3)

2 3

3

Na COSoda Ash mg/L = Non-Carbonate Hardness ×

CaCO Equation 3.2

So,

Soda Ash (mg/L) = mg/L Non-Carbonate Hardness as CaCO3 x Na2CO3/CaCO3

= mg/L Non-Carbonate Hardness as CaCO3 x 106/100

= mg/L Non-Carbonate Hardness as CaCO3 x 1.06

Magnesium Salt (MgO)

MM

ggO

OMg required Mg. Hardness

M (m /L =

gg )

Equation 3.3

Where,

Mg required (mg/L Mg2+) = mg/L SiO2 x 2

Mg Hardness (mg/L Mg2+) = mg/L CaCO3 x 24.3/100

c. Duraflow MF

After chemical treatment, settable and un-settable solid particles, ready to precipitate, are

removed by Duraflow DF 401 directly.

Duraflow DF-401, tubular membrane configuration, was designed to handle high solid

concentration. The membranes, made of PVDF, were cast on the surface of porous polymeric

tubes to produce a nominal pore size of 0.1 micron. The detail specification of DF 401 is

shown in Table 3.3 and Figure 3.8.

44

Table 3.3 Specification of Duraflow Membrane


Membrane company name Duraflow LLC

Membrane model DF-401

Configuration Tubular (inside-outside)

Size 38.1 mm (1.5 inches) diameter, 914.4 mm long

Number of Tube 1 each 1 inches diameter

Total Surface Area 0.28 m2

Shell construction Schedule 40 PVC with a 0.5 inch OD filtrate port

and union connection on each end

Operating pressure (maximum) 4.2 bar (60 PSI)

Pore size 0.1 micron Nominal

Operating temperature (maximum) 43.330C

Rated flow at 2.76 bar (40 PSI) : 2.76 – 5.45 m3/d

Membrane Material PVDF

Flux (maximum) 1,622 LMH

Figure 3.8 Duraflow DF-401

RO System

The reverse osmosis system was designed to remove residual impurity in the water after MF

such TDS and other ionic compounds. Permeate of RO was recycled back to cooling tower,

and used as make-up water.

Hydranautic CPA2-4040 RO membrane, spiral wound configuration, was applied in this

study for both stages of RO. Membrane specification is given in the Table 3.4.

Table 3.4 Specification of Hydranautics CPA2-4040


Membrane company name Nitto Denko

Maximum Applied Pressure 41.6 bar

Maximum Chlorine Concentration <0.1 PPM

Maximum Operating Temperature 450C

45


Feedwater pH range 3-10

Maximum Feedwater Turbidity 1 NTU

Maximum Feedwater SDI15 5

Maximum Feed Flow 3.6m3/h

Minimum Ratio of concentration

to Permeate Flow for any Element 5:1

Configuration Spiral wound

Membrane Polymer Composite Polyamide

Nominal Membrane Area 7.9 m2

Permeate Flow 8.5 m3/d

Salt Rejection 99.5% (99.2% minimum)

Flux (maximum) 44.83 LMH

Dimension 100 mm (4”) diameter x 1016 mm (40”) length

Weight 3.6 kg

Figure 3.9 Hydranautics CPA2-4040

Other sub-equipment

Table 3.5 presents other sub-equipment and its function used in the system.

Table 3.5 Function of Other Sub-equipment of System

Item Function

Feed pump Supply water to unit operation

Circulation pump Increase cross flow velocity

High pressure pump Supply water to RO membrane with high applied pressure

Flow meter Indicate flow rate

Pressure gauge Give pressure information

pH meter Show the level of pH, used in chemical precipitation

Thermometer Indicate feed temperature

RO pre-filter Role as safety guard of RO (5 micron cartridge filter)

46

3.6 Experimental Set-up

Figure 3.10 describes the process flow diagram of experimental set-up. Feed water was taken

from drain pit of CTBD treatment plant in TPAC, and store in one cubic meter feed tank.

The feed water was flowed to top of ceramic membrane house by feed pump, and permeate

water was collected on the side of membrane. At the bottom of the house, concentrate was

collected and circulate back to feed tank. In order to increase cross flow velocity, circulation

pump was installed after feed pump. Another feed pump of first stage RO pumped the

permeate water of ceramic pass through RO pre-filter (cartridge filer), and high pressure

pump further pressurized water to RO unit. The permeate water was sent to RO water tank,

and concentrate went to second stage RO system.

The concentrate water from first stage RO was kept in chemical precipitation tank where

Soda ash and magnesium oxide were added to precipitate hardness and silica. The optimum

dosage got from bench test was used, and mixed by feed pump through by-pass line. 10

minutes of mixing time was given for MgO before adding Na2CO3, then pH was adjusted to

9.5 and 11 for 30 minutes of reaction time for each pH value. The ready to precipitate

particles were separated from water by Duraflow with 0.1 micron pore size. The concentrate

of Duraflow went back to chemical precipitation tank. The same thing as first stage RO,

permeate from Duraflow passed through pre-filter by feed pump, and fed to second stage

RO by high pressure pump.

For both RO stages, feed pressure was varied: 6 to15 bar for first stage RO, and 10 to18 bar

for second stage RO. The flux, water recovery, rejection, water quality and economization

were the key tools to find out the optimum condition of system. Samples were collected at

feed, concentrate, and permeate side of all membranes system, and analyzed in LPE’s

laboratory.

3.7 Operational Condition

The system worked under 220 v and 50 Hz following each equipment specification. The

major operation condition are given in Table 3.6.

Table 3.6 Operational Condition of ZLD System

Items Unit Status Description

Ceramic

membrane

Membrane type - Fixed CMF2-M-200

Feed pressure bar Fixed 3

Surface area m2 Fixed 0.22

Pore size μm Fixed 0.2

Duraflow

Membrane type - Fixed Duraflow DF 401

Feed pressure bar Fixed 2


Pore size μm Fixed 0.1

RO

Membrane type - Fixed Hydranautics CPA2-4040


Feed pressure bar Varied RO-1: 6, 8, 10, 12 and 15

RO-2: 10, 12, 14, 16, and 18

47

Items Unit Status Description

Chemical

Precipitation

Retention time min Fixed 10 min for MgO mixing, pH=9.5

for 30 min, and pH=11 for 30 min

Chemical type - Fixed Na2CO3, and MgO

Dosage mg/L Varied MgO=1000, 2000, and 3000

Na2CO3=50, 150, and 250

Other Temperature 0C Fixed 25-35*

*: Flux normalization by temperature correction factor @ 250C

Due to the fluctuation of operating temperature, it resulted in variation of permeate flow.

Temperature correction methods differ by membrane manufacturer, but always result in

decreasing corrected flow with increasing temperature. It is very important to normalized

the flow into one temperature, and equation 3.5 and 3.6 are the typical formula in normalize

the flow (Allgeier et al., 2005).

Flow Normalization

025 tCQ Q TCF Equation 3.5

Where: Q25oC : Normalized flux at 25 oC (LMH)

Qt : Actual flux at temperature t (LMH)

TCF : Temperature correction factor (dimensionless)

Temperature Correction Factor (TCF)

1 1exp

273 298TCF K

t

Equation 3.6

Where: TCF : Temperature correction factor (dimensionless)

K : Membrane-specific manufacturer-supplied constant (1/K)

K=2700 for hydranautic membrane

t : Operating temperature (oC)

3.7.1 Operational scenarios

In order to find out the optimum condition for ZLD system, the scenarios in Table 3.7 were

applied, and only chemical dosage and feed pressure of RO were varied.

48

Table 3.7 Operational Scenario of ZLD System

Phase Scenario

Chemical dosage

(mg/L) Pressure

(bar)

Duration

(day) Remark

Na2CO3 MgCl2

1 1 - - 3 2 Ceramic membrane

(RO-1 pretreatment)

2

2

- -

6

5 RO-1 optimization

condition

3 8

4 12

5 15

3

6 50 1,000

- 14 Optimization dosage

by bench test

7 50 1,000

8 50 1,000

9 150 2,000

10 150 2,000

11 150 2,000

12 250 3,000

13 250 3,000

14 250 3,000

4 15 Optimum dosage 2 1 Duraflow (remove

hardness and silica)

5

16

Optimum dosage

10

5 RO-2 optimization

condition

17 12

18 14

19 16

20 18

3.7.2 Chemical dosage optimization

In this chemical optimization stage, soda ash (Na2CO3) was used to remove non-carbonate

hardness, and magnesium oxide (MgO) was added to precipitate silica. Moreover, sodium

hydroxide was added to adjust pH for hardness precipitation. The tests were conducted in

LPE laboratory at room temperature (25-28oC) using a standard one liter beaker, but only

500mL of water sample was used. The procedure was finalized by the recommendation from

Duraflow LLC and the consultation from LPE.

Test Procedure:

500mL of water sample was used, and mixed with MgO for 10 minutes before adding

Na2CO3.

After adding both MgO and Na2CO3, NaOH was used to adjust pH to 9.5 for calcium

precipitation, and continued mixing for 30 minutes.

After 30 minutes, pH was adjusted again to 11 by NaOH for magnesium precipitation

and mixed for another 30 minutes. During magnesium precipitation, silica also

removed by adsorbs with magnesium hydroxide.

Water sample was filtrated with 2.5 micron of filter paper, and filtrate was analyzed

for conductivity, pH, hardness, alkalinity, and silica residual.

49

3.8 Analytical Parameters and Methods

Analytical parameters and methods are given in Table 3.9. In addition, sampling locations

of each parameter are also mentioned. All samples and parameters were measured in LPE’s

laboratory.

3.9 Engineering Design and Cost Information

Engineering design of ZLD system was done by using the result from first and second

objective of research. In water auditing, average daily wastewater discharges was around

180 m3/day. With 2 as safety factor, maximum design flow rate was 360 m3/day. The main

reason of this selection were to avoid shock peak flow and for future expansion of the plant.

In RO system design, Hydranautics Membrane Solutions Design 2012 (IMSDesign®) was

utilized to simulate the system. This simulation software is a freeware which provided by

Hydranautics for designing membrane system by using Hydranautics membrane.

IMSDesign® is an accurate prediction of performance over time and under a variety of

conditions. Parameters such as salt passage increase and flux decline due to fouling are

simply reachable to the user. The information used in the membrane selection process is

provided by program, and users can completely control it (Hydranautics, 2013).

Depending on the result of experiment, however, ceramic membrane and Duraflow system

were designed manually. Average flux was a vital tool to calculate membrane filtration area

and quantity of membrane elements as well.

By consultation with LPE, cost information of whole system were clearly estimated. Cost of

each unit equipment was provided by LPE store manager, and LPE equipment suppliers. All

of cost information in US currency were converted to Thai Baht currency with normal

exchange rate, one USD equal around 32 Thai Baht in February 2014. Due to confidential

of cost information of Company, it was shown only macro scale of information, and not a

micro one. Major equipment to estimate the cost is shown in Table 3.8.

Table 3.8 Major Equipment for Cost Information

Equipment Description

Ceramic MF system

Including pump, membrane, housing/vessel, valve, pH

meters, pressure gauges, tanks, etc.

First stage RO system

Second stage RO system

Duraflow MF system with

chemical precipitation

Pipes ∅100mm (4”), ∅80mm (3”), ∅60mm (2.5”), and

∅50mm (2”)

Installation and Labor cost -

Skid and Accessories -

Control Panel and Power cable -

http://www.membranes.com/index.php?pagename=imsdesign

50

3.10 Performance Evaluation and Criteria of System Design

3.10.1 Water Recovery

Due to system was running in batch mode, the water recovery was calculated based on

volume of feed water, permeate water and concentrate water of each membrane unit and

whole system. Following Equation 3.5 was used to calculate water recovery of system

(Visvanathan, 2013).

P

F

VWater recovery (Y)= × 100%

V Equation 3.5

Where: Y : Water recovery rate (%)

VP : Volume of permeate water (m3)

VF : Volume of feed water (m3)

3.10.2 Rejection

P

F

CRejection (R)= 1 ×100%

C

Equation 3.6

Where: R : Rejection rate (%)

CP : Concentration of permeate water (mg/L)

CF : Concentration of feed water (mg/L)

3.10.3 Flux

PQFlux (J)=

A Equation 3.7

Where: J : Permeate flux (L/m2.h)

QP : Permeate flow rate (m3/h)

A : Effective membrane area (m2)

3.10.4 Tran Membrane Pressure

For Cross flow mode:

F CTM P

P PP = P

2

Equation 3.8

Where: PTM : Tran membrane pressure (bar)

PF : Pressure at feed side (bar)

PC : Pressure at concentrate side (bar)

PP : Pressure at permeate side (bar)

51

3.10.5 Osmotic pressure

According to Hydranautics (2013), osmotic pressure, π, of a solution can be determined

experimentally by measuring the concentration of dissolved salts in solution:

1.19 ( 273) ( )iT m Equation 3.9

Where: π : Osmotic pressure (psi)

T : Temperature (oC)

∑mi : Sum of molarity concentration of all constituents in a solution (moles

of solute/kg of solvent)

However, as the role of thumb for estimation osmotic pressure (π), assuming that 1000 mg/L

(ppm) of Total Dissolve Solids (TDS) equal about 11 psi (0.76 bar) of osmotic pressure

(Hydranautics, 2013).

According to Visvanathan (2013), in RO application, feed pressure equals around 4 to 20

times of osmotic pressure.

52

Figure 3.10 Experimental set-up of ZLD system

53

Table 3.9 Analytical Parameters and Method

Parameter Units Analytical

method Sampling Location Interference

Applicable

accuracy/range Reference

pH - Electrometric Feed, permeate, and

rejection of membranes

Undesirable matter attached to

electrode 1-14

APHA et al.

(2012)

Turbidity NTU Nelphelometric Feed, permeate, and


Color or suspended matter in

large amounts

APHA et al.

(2012)

Conductivity µS/cm Conductivity

meter

Feed, permeate, and

rejection of membranes - TDS/EC=0.55-0.7

APHA et al.

(2012)


meter

Feed, permeate, and

rejection of membranes - TDS/EC=0.55-0.7

APHA et al.

(2012)

Alkalinity mg/L as

CaCO3 Titration

Feed, permeate, and


Soaps, oily matter, suspended

solids, or precipitates may coat

the glass electrode.

- APHA et al.

(2012)

Total

Hardness

mg/L as

CaCO3

EDTA

Titrimetric

Feed, permeate, and

rejection of membranes - -

APHA et al.

(2012)

Calcium

Hardness

mg/L as

CaCO3

EDTA

Titrimetric

Feed, permeate, and

rejection of membranes - -

APHA et al.

(2012)

Chloride mg/L as

Cl- Argentometric Feed water , feed and

permeate RO

Bromide, Iodine, Cyanide,

Orthophosphate, iron, sulfide,

thiosulfiate, and sulfite ions

- APHA et al.

(2012)

Sulfate mg/L as

SO4-2 Turbidimetric

Feed, reject, and

permeate RO

Max. curve=40

mg/L

APHA et al.

(2012)

Silica mg/L as

SiO2 Molybdosilicate

Feed, permeate, and

rejection of membranes Glass material Max. curve=5 mg/L

APHA et al.

(2012)

Free Chlorine mg/L as

Cl2 Photometer Feed RO Color and turbidity may interfere - -

54

Chapter 4

Results and Discussions

This chapter presents the results which reflects to the objectives listed in Chapter I. It consists

three main parts such as water auditing of CTBD treatment plant of TPAC, pilot scale

experiment of ZLD system, and as well as engineering design and cost information of the

proposed system. Firstly, water auditing was conducting in the existing CTBD treatment

plant of TPAC to investigate the performance of that plant, and also to figure how much

wastewater were discharged from that plant every day. Secondly, real wastewater was

collected from drain pit of CTBD treatment plant of TPAC, which was discharged out of the

plant, to run pilot scale experiment in LPE. The last part is engineering design of ZLD system

and providing an estimated cost information of both investment cost and O&M cost.

Moreover, cost of treatment with designed ZLD system was estimated and compared with

the current situation of TPAC (purchasing industrial water).

4.1 Water Auditing

4.1.1 Cooling tower blowdown treatment plant in TPAC

Water auditing was primarily concentrated on CTBD treatment plant in TPAC where all of

blowdown from cooling tower were treated and reused by UF and RO system. UF is mainly

used pretreatment unit for RO system to remove suspended solids and other foulants matters.

Besides, in order to avoid RO membrane destruction from chlorine, activated carbon filter

was placed before RO system to remove all residual chlorine. Moreover, NaOCl and HCl

were used in UF chemical enhance backwash (CEB) to remove all organic and inorganic

foulants.

Only permeate water from RO system were reused in cooling tower. Other rejection or

backwash such as UF backwash, UF CEB, RO rejection, RO flush, and RO CIP were drained

to drain pit which periodically discharged from TPAC.

Figure 4.1 Flow diagram of CTBD treatment plant in TPAC

55

4.1.2 Water auditing data

For water auditing in CTBD treatment plant in TPAC, water balance and salt balance played

a very vital role in plant’s evaluation. Thus, 76 days of data were recorded from data loggers

and flow meters, and characteristic of water samples were analyzed in LPE laboratory.

Accumulative water volume and running hour of UF plant (backwash and feed) and RO

plant (permeate and rejection) were recorded since October 3, 2013 until December 18, 2013

from data logger. To do so, an average flow in cubic meter per day was able to observe as

show in Table 4.1.

Table 4.1 Accumulative Water Volume and Running Hour of UF and RO Plant

CTBD

Treatment

Plant

Accumulate volume

(m3)

Accumulate running hour

(h) Total

days h/d m3/d

3/10/2013 18/12/2013 3/10/2013 18/12/2013

UF BW 8,196.5 13,100

1324 2422

76

14.45 64.52

Feed 48,754.3 94,010 595.47

RO Reject 11,972 20,340

756 1312 7.32 110.11

Per. 25,828 43,927 238.14

Total Volume:

total end startV AV AV Equation 4.1

Where Vtotal : Total water volume from starting day of water audit until the end day

(m3)

AVstart : Accumulative volume read from data logger at starting day of water audit

(m3)

AVend : Accumulative volume read from data logger at end day of water audit

(m3)

Total Running Hour (h)

total end startH AH AH Equation 4.2

Where Htotal : Total running hour from starting day of water audit until the end day (h)

AHstart : Accumulative running hour read from data logger at starting day of water

audit (m3)

AHend : Accumulative running hour read from data logger at end day of water

audit (m3)

Average Running Hour per Day (h/d)

total

total

HHD

D Equation 4.3

Where HD : Average running hour per day (h/d)

56

Htotal : Total running hour from starting day of water audit until the end day (h)

Dtotal : Total day of water auditing period (d)

Average Flow per Day (m3/d)

total

total

VQ

D Equation 4.4

Where Q : Average flow per day (m3/d)

Vtotal : Total water volume from starting day of water audit until the end day (m3)

Dtotal : Total day of water auditing period (d)

4.1.3 Water analysis

In CTBD treatment plant of TPAC, some important points of unit operation such as CTBD,

UF and RO had sampled and analyzed in order to figure out its characteristic. As the result,

Table 4.2 and Figure 4.2 clearly shows the characteristic of different sample point in CTBD

treatment plant. Moreover, these data were just the average value from 3 times water

sampling.

57

Table 4.2 Characteristic of Water Samples of CTBD Treatment Plant

Parameter Unit Method

CTBD Treatment Plant in TPAC

CTBD Product

UF Feed RO

UF

Backwash

UF

CEB

Permeate

RO

Reject

RO

RO

Flush Drain Pit

Appearance - Observation - Clear Clear Brown &

Turbid

Slightly

turbid Clear Clear Clear

Yellowish

& Turbid

Turbidity NTU Nephelometric 2.3 0.4 0.4 72.9 3.8 <0.1 0.35 0.4 22.3

pH (at 250C) - Electrometric 8.2 8.2 8.2 8.04 5 7.365 8.175 8.3 8.18

Conductivity μS.cm-1 Conductivity

meter 387.5 397 399.5 408 830 14.93 1147 1099 450


meter 252 258.05 259.68 265.2 540 8.22 745.5 714.35 292.5

P- Alkalinity mg/L as

CaCO3 Titration 0 0 0 0 0 0 0 0 0

M-Alkalinity mg/L as

CaCO3 Titration 85.8 85 85 110 <5 <5.00 247.2 240 102.5

Total

Hardness

mg/L as

CaCO3

EDTA

Titrimetric 89.225 90.9 90.9 116.15 136.35 2.37 270.45 252.5 103.525

Calcium

Hardness

mg/L as

CaCO3

EDTA

Titrimetric 56.95 72.8 72.8 83.2 93.6 1.34 181.15 187.2 83.2

Chloride mg/L as

Cl- Aegentometric 44.67 48.92 47.115 41.58 185.9 0.505 144.07 132.09 94.175

Sulfate mg/L as

SO4-2

Turbidimetric 21.2 33.76 29.89 7.16 36 Bdl 47.6 79.5 26.75

Silica mg/L as

SiO2 Molybdosilicate 22.635 19.52 19.16 217.18 29.94 Bdl 47.04 54.63 245.69

58

Figure 4.2 Overall information of flow rate and TDS of CTBD treatment plant

59

As per result from Table 4.1, 4.2 and Figure 4.2, the flow rate (Q), TDS concentration (X),

and salt content of input and output of the plant could be summarized as following Table

4.3.

Table 4.3 Summary of Input and Output of CTBD Treatment Plant

Parameter Flow (m3/d) TDS (mg/L) Salt (g/d)

Feed (CTBD) 595 252 150,058

ACF Backwash 4.57 259.68 1,187

UF CEB 5.33 540 2,878

UF Backwash 64.52 265.2 17,111

RO permeate 238.14 8.22 1,958

RO reject 110.11 745.5 82,083

RO flush 3.66 714.35 2,613

NaOCl 1.4710-3 100,000 147

HCl 0.8210-3 350,000 287

4.1.4 Water balance

Total volume of input of plant was 595 m3/d and total output was 426.33 m3/d .

595 426.33

% 100% 28.40%595

Accuracy

Figure 4.3 Water balance

4.1.5 Salt balance

Amount of salt content of input and output in the plant was calculated from multiplication

of flow rate with TDS concentration, and total salt input was 150,492 g/d and 107,830 g/d

for total salt output.

150.492 107,830

150.492% 100% 28.35%Accuracy

60

Figure 4.4 Salt balance

4.1.6 Discussion

Figure 4.5 Flow rate and salt content of each water stream

In accordance with water auditing result which is shown in Figure 4.5, RO reject was

observed the highest salt content among all water streams of put, 82 kg/day of salt. Also, salt

content in UF backwash stream was around 17 kg/day of salt which was the second highest.

Additionally, flow rate of RO reject was seen pretty high after that of RO permeate which

consisted low salt content, and followed by UF backwash. From this point of view, UF

backwash, RO reject, and RO permeate were the major stream in CTBD treatment plant.

However, the summation flow rate of UF backwash, UF CEB, RO reject, and RO flush,

which were discharging out of the plant every day, was around 180 m3/day (Figure 4.2).

With this large amount of wastewater, further treatment technologies need to be considered

in order to minimize or reuse it in industrial processes.

Referring to the result from water and salt balance above, both percentage of different

between input and output is less than 30%. Thus, it showed that the plant was running under

well control, and might not have any serious problems or any leakages (Visvanathan, 2004).

0

100

200

300

400

500

600

Feed

(CTBD)

ACF

Backwash

UF CEB UF

Backwash

RO

permeate

RO reject RO flush

Flo

w (

m3/d

)

Sal

t (k

g/d

)

Flow rate Salt content

61

However, the possible reasons which caused this such a high difference between input and

output could be listed as following:

All flow rate data were the average number.

Some portion of water still remained in the system, membranes and tanks.

Inaccurate of flow meter (Rota meter flow) of some water stream like RO flush and

Activated carbon filter backwash (ACF BW).

System was running in batch mode.

4.2 ZLD Pilot Scale Experiment

According to the result got from water auditing in CTBD treatment plant of TPAC, large

portion of wastewater (180m3/day) was discharged every day, and that need further treatment

system. ZLD system was designed to recover that big portion of wastewater. To understand

the performance of system, pilot scale experiment was conducted.

Pilot scale experiment was designed with two stage of RO system in order to recovery as

much as water. Nevertheless, both stages of RO consisted different kind of pretreatment

system regarding to characteristic of feed water of each stage. Feed water was collected

directly from drain pit of CTBD treatment plant in TPAC where UF backwash and CEB,

and RO reject and flush were discharged. Table 4.4 below illustrates the characteristic of

feed water.

Table 4.4 Feed Water Characteristic

Parameter Unit Method Reference Method Feed Water

Appearance - Observation APHA (2012), 2110 Slightly

Turbid

Turbidity NTU Nephelometric APHA (2012), 2130 (B) 1.7

pH (at 250C) - Electrometric APHA (2012), 4500-H (B) 7.9

Conductivity μS.cm-1 Conductivity

meter APHA (2012), 2510 B 657


meter APHA (2012), 2510 A 427

P- Alkalinity mg/ L as CaCO3 Titration APHA (2012), 2320 (B) Nil

M-Alkalinity mg/ L as CaCO3 Titration APHA (2012), 2320 (B) 115

Total

Hardness mg/ L as CaCO3

EDTA

Titrimetric APHA (2012), 2340 (C) 156.55

Calcium

Hardness mg/ L as CaCO3

EDTA

Titrimetric APHA (2012), 3500-Ca (B) 109.2

Chloride mg/ L as Cl- Aegentometric APHA (2012), 4500 Cl- (B) 86.85

Sulfate mg/ L as SO4-2 Turbidimetric APHA (2012), 4500 -SO4-2 (E) 38.18

Silica mg/ L as SiO2 Molybdosilicate APHA (2012), 4500 –SiO2 (C) 43.63

Free Chlorine mg/ L as Cl2 Photometer - 0.01

From membrane fouling standpoint, an SDI < 5, is equivalent to a Turbidity < 1 NTU ("Silt Density Index

(SDI) Measurement & Testing," 2007)

62

4.2.1 First stage RO (RO-1) experiment

a. First stage RO pretreatment

For the first stage RO system, ceramic membrane was selected as pretreatment system. With

0.22 m2 membrane surface area of ceramic membrane, one cubic meter of water sample was

run for 8 hours of operation time. Feed pressure was fixed at 3 bars, and every one hour

sample was collected to check turbidity of permeate water. The result of flux and tran-

membrane pressure (TMP) is shown in Figure 4.6.

Figure 4.6 Flux and TMP of ceramic membrane

Tran-membrane pressure kept constant while flux was declined over the time, but it looked

stable after 5 hours of experimental time. The reason behind the declination of flux was

because of feed turbidity in feed tank kept increasing, as shown in Figure 4.6. Samples were

collected and were analyzed in LPE laboratory. As the result, average turbidity was only

0.18 NTU which was good enough as RO feed. The criteria of RO feed was less than 1 NTU

of turbidity. Other results of experiment were attached in Appendix B, Table B.1.

Moreover, a very high water recovery was achieved in this experiment, 97.8%, since 978 L

of permeate was collected, and only 22 L was concentrate water which was rich of suspended

solids. That concentrate was possibly further sent to dewatering processes like sludge

thickener or filter press.

This flux result was much better comparing to the previous pilot test with the same pilot unit,

Case #3 in Appendix C, but different feed characteristic. Similarly, turbidity removal was

lower than in that previous pilot test due to higher feed pressure was applied.

b. First stage RO optimization

RO-1 optimization was focused on rejection rate of silica, hardness, and TDS as major tools

in evaluation with the variation of feed pressure from 6 to15 bar to understand optimum

condition. In relation to feed concentration, feed osmotic pressure was calculated and

equaled 4.65 psi (0.32 bar).

0

2

4

6

8

10

12

350

450

550

650

750

850

0 60 120 180 240 300 360 420 480

TM

P (

bar

)

Turb

idit

y (

NT

U)

Flu

x (

LM

H)

Operation Time (min)

Flux (LMH) Feed Turbidity TMP

63

In the optimization process, feed pressure was varied every one hour from 6, 8, 10, 12, and

15 bar. One water sample was collected for each feed pressure to analyze TDS, turbidity,

hardness and silica. Other important data such as flow rate, temperature, and outlet pressure

were recorded as well which was shown in Table B.2 of Appendix B.

According to Figure 4.7, 8 bars pressure was considered as the optimum pressure in term of

rejection and economic if compared to the other pressures, especially 10 bars. 10 bars of feed

pressure has a better rejection rate of hardness and silica, and even higher average flux.

However, the differences were not significant if economization of operation cost was

considered.

Figure 4.7 Rejection rate and flux with different feed pressure

c. First stage RO with optimum condition

Figure 4.8 Flux and TMP of RO-1 at 8 bar feed pressure

0

10

20

30

40

86

88

90

92

94

96

98

100

5 6 7 8 9 10 11 12 13 14 15 16

Flu

x (

LM

H)

% R

ejec

tio

n

Feed Pressure (bar)

% TDS % Hardness % Silica Flux

2

4

6

8

10

12

14

16

15

16

17

18

19

20

21

22

23

24

0 60 120 180 240

TM

P (

bar

)

Fee

d S

alin

ity (

mg/L

)

Flu

x (

LM

H)


Flux (LMH) TMP Feed Salinity (x100)

64

With 8 bars feed pressure, all water samples (permeate from ceramic membrane) were

utilized in experiment. Experimental conditions in this stage was followed the condition in

optimization. On the other hand, feed salinity was measured hourly in order to see the

development of salinity in feed tank.

75 % water recovery was fixed while feed water was around 950 L; thus only 230 L of

concentrate was collected. Moreover, due to continuously increasing of feed concentration,

flux was also declined from time to time as well (Figure 4.8).

Table B.3 in Appendix B is shown all experimental result of this first stage RO system, and

average flux was observed more than 20 LMH which is better than average flux of RO

system from Hydranautic Projection Software, Figure E.1 in Appendix E.

TDS concentration of feed, permeate, and concentrate were 435.5mg/L, 32.4mg/L, and

1,443mg/L respectively, and the whole result is tabled in Table 4.5. Referring to this result,

more than 92% of rejection was achieved for both TDS and total hardness. Nevertheless,

only 83.57% of silica removal was observed.

Table 4.5 Result of RO-1 Experiment with Optimum Pressure

Parameter Unit Feed RO-1 Permeate

RO-1 Reject RO-1

Rejection

(%)

Appearance - Slightly

yellow clear

Yellow and

slightly turbid -

Turbidity NTU 0.18 <0.1 1.4 -

pH - 7.6 7.2 8.14 -

Conductivity µS/cm 670 58.2 2,220 -

TDS mg/L 435.5 32.4 1,443 92.56

P-Alkalinity mg/L as CaCO3 0 0 0 -

M-Alkalinity mg/L as CaCO3 125 10 450 92

Total Hardness mg/L as CaCO3 151.5 8.08 595.9 94.67

Calcium Hardness mg/L as CaCO3 104 2.08 405.6 98

Chloride mg/L as Cl- 84.37 6.95 307.71 91.76

Silica mg/L as SiO2 43.63 7.17 170.04 83.57

4.2.2 Second stage RO experiment

a. Bench test for chemical precipitation

Bench test of chemical precipitation had taken place in LPE laboratory in order to figure out

the optimum chemical dosage. MgO and Na2CO3 were used to precipitate silica and hardness

respectively. Moreover, NaOH was added in order to adjust pH to 9.5 and 11 (two stages),

and test procedure was followed the procedure as stated in Chapter 3, section 3.5.5. In the

bench test, chemical dosage was varied: Na2CO3 (50, 150, and 250 mg/L); and MgO (1000,

2000, and 3000 mg/L). The average result of the whole bench test is shown in Table 4.6 and

Figure 4.9, and the detail result could be found in Table B.4 in Appendix B.

65

Table 4.6 Result of Chemical Precipitation Optimization

Test No Conduct.

(µS/cm) pH

Hardness (mg/L) Alkalinity (mg/L) Silica

T. Hardness Ca. Hardness P M (mg/L)

1 2890 10.66 165.81 161.2 380 336.67 53.87

2 2903 10.67 161.60 157.73 376.67 316.67 42.04

3 2750 10.55 159.92 145.6 318.33 310 29.36

4 2880 10.65 171.7 164.67 483.33 353.33 67.01

5 3060 10.72 168.33 152.53 420 381.67 46.39

6 2943 10.55 158.23 155.92 378.33 361.67 31.63

7 3123 10.69 166.65 152.53 446.67 400 64.5

8 3080 10.79 166.65 161.2 475 375 43.31

9 3067 10.83 168.33 156.18 468.33 363.33 37.48

Sample No 1 2 3 4 5 6 7 8 9

Na2CO3 (mg/L) 50 50 50 150 150 150 250 250 250

MgO (mg/L) 1000 2000 3000 1000 2000 3000 1000 2000 3000

Figure 4.9 Result of total hardness and silica residual of bench test

According to result above, sample No 3 with 50 mg/L of Na2CO3 and 3000 mg/L MgO was

seem like the optimum dosage due to its silica residual. However, to make sure that it was

the best dosage, an additional experiment was taken place by fixing 50mg/L of Na2CO3, and

varying MgO from 500, 1000, 1500, 2000, 2500, 3000, 3500, and 4000 mg/L. The purpose

of this additional experiment was to find out the reduction rate of silica with the addition of

MgO.

The result from Figure 4.10 shows that 3000mg/L of MgO was the best in term of removal

rate of silica and economic. Silica residual of 3500 and 4000 mg/L of MgO was almost the

same, and only few ppm of silica was reduced compare to that of 3000 mg/L of MgO.

0

20

40

60

80

100

120

140

160

180

1 2 3 4 5 6 7 8 9

Res

idual

co

nce

ntr

atio

n (

mg/L

)

Sample No

Total Hardness Silica

66

Figure 4.10 Silica reduction with MgO added

This result was similar to what Suciu & Miller (1980) stated in their report about reduction

of silica with addition of MgO. The reduction of silica by addition of MgO tended to be

stable or almost stable at some points. However, the usage of MgO concentration in this case

was substaintially higher than Suciu & Miller (1980)’s report (referring to section 2.7.3 in

Chapter 2). This differences were because of temperture of water sample (high temperature,

high removal rate) and feed concentration.

In conclusion, 3000mg/L of MgO with 50mg/L Na2CO3 was the optimum dosage for this

water characteristic in term of silica residual and economization of operation cost.

b. Performance comparison of chemical treatment between sludge removal and

non-sludge Removal

Procedure

This experiment was an additional experiment in order to finalize the process of chemical

treatment whether sludge need to be removed before feed to Duraflow MF or not.

For both cases, same experiment procedure was conducted with the same amount of water

sample. However, for sludge removal case, one hour of settling time was provided for sludge

settling before it was removed. The procedure is shown as following:

- Prepared 150 liters of water sample.

- Added 450g of MgO (3000mg/L) and mixed thoroughly for 10 minutes.

- Added 7.5g of Na2CO3 (50mg/L), and pH should be around 9.5. If not, NaOH need

to be added to adjust pH to 9.5. Reaction time was 30 minutes.

- Adjusted pH to 11 with NaOH and mixed for another 30 minutes.

- Allow sludge to settle for one hour, only for sludge removal case, then run with

Duraflow.

20

30

40

50

60

70

80

500 1000 1500 2000 2500 3000 3500 4000

Sil

ica

resi

dual

(m

g/L

)

MgO Added (mg/L)

67

Operation Result

Table 4.7 Operation Data of Both Cases at 2 bar Feed Pressure

Time Sludge Removal Non-sludge Removal

Flowrates (LPH) Flux (LMH) Flowrates (LPH) Flux (LMH)

0 200 714.29 200 714.29

10 180 642.86 160 571.43

20 160 571.43 150 535.71

30 130 464.29 120 428.57

40 100 357.14 90 321.43

50 95 339.29 85 303.57

60 95 339.29 80 285.71

70 95 339.29 75 267.86

80 95 339.29 70 250.00

90 95 339.29 65 232.14

Note: Inlet pressure: 2 bar (fixed)

Outlet pressure: 0.75 bar (constant)

Different pressure: 1.25 bar (constant)

According to result from Table 4.7 above, flux comparison of both case are able to present

as shown in Figure 4.11. Referring to this results from experiment of both cases, flux of

sludge removal case was a bit stable and higher than that of non-sludge removal case if

compare to the same operation time.

Figure 4.11 Flux comparison for both cases

Besides, result of water recovery and rejection performance are summarized in Figure 4.12.

Apart from flux result, analytical result of permeate of both cases identifies that the removal

0

0.5

1

1.5

2

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70 80 90

Pre

ssure

(b

ar)

Flu

x (

LM

H)

Time (min)

Sludge Removal Non-Sludge Removal ΔP

68

rate of hardness and silica of non-sludge removal were significantly higher than another case.

Moreover, its water recovery was also 13% higher than sludge removal case.

Figure 4.12 Permeate result of both cases

In conclusion, non-sludge removal case was better than sludge removal case in term of

removal ability and water recovery. Thus, Duraflow pilot experiment was decided to run

without sludge removal even though it will cause flux declination compared to sludge

removal. This problem will be solved by flushing membrane periodically during operation.

c. Duraflow Experiment with Chemical Precipitation

With the optimum dosage from bench test, chemical precipitation was done with 205 liters

of water sample which was the concentrate of first stage RO system by following the same

procedure of bench test. 10.25g of Na2CO3 (50 mg/L) and 615g of MgO (3000 mg/L) was

used.

After chemical precipitation was done, water sample was directly run with Duraflow MF

system without sludge settling. As state in previous section, performance comparison of

chemical treatment between sludge removal and non-sludge removal, non-sludge removal

case was better than sludge removal case in term of removal ability and water recovery. That

was the reason why water was fed directly with Duraflow after chemical precipitation.

In the pilot experiment, feed pressure was fixed at 2 bar. Operational data were recorded

every 10 minutes of operation time, and samples was collected hourly. For the first 2 hours,

experiment was run with recirculation mode to see the tendency of flux, then once through

was run to take the permeate out for the rest of operation time.

25

120

82.4

27.54

53.33

24

60

20.6

19.81

66.67

0 20 40 60 80 100 120

Conductivity (µS/cm) x100

Total Hardness

Ca Hardness (mg/L as CaCO3)

Silica (mg/L as SiO2)

Water Recovery (%)

Non-sludge removal Sludge removal

69

Figure 4.13 Flux and TMP of Duraflow MF

Referring to Figure 4.13, the flux declined rapidly from 1000 LMH to 317 LMH during 2

hours of recirculation mode. Then flux kept slightly decreasing to less than 200 LMH for

another 2 hours. By comparing to Case Study #2 in Appendix C, it was noticed that flux of

this case was dropped faster, and was lower than the flux in Case Study #2. After finished

the experiment, permeate was neutralized from pH of 11 to pH of 8 with HCl (17%).

Water samples were collected at permeate side: one before neutralized and another one after

neutralized, and the result from water analysis is summarized as following:

Table 4.8 Before and After Neutralized of Duraflow Permeate

Parameter Unit Feed Permeate (before

neutralized)

Permeate (after

neutralized)

Turbidity NTU 1.4 0.3 0.3

pH - 8.14 11.02 8.35

Conductivity µS/cm 2,220 2,670 2,650

TDS mg/L 1,443 1,736 1,723

Total Hardness mg/L as CaCO3 595.9 152.67 151.5

Silica mg/L as SiO2 170.04 8.95 8.94

Free chlorine mg/L as Cl2 - - 0.07

d. Second stage RO optimization

RO-2 optimization was taken place by varying the feed pressure: 10, 12, 14, 16, and 18 bar,

while osmotic pressure of feed was 18.95 psi (1.31 bar). The main tools for selection the

optimum pressure were the rejection of TDS, hardness, and silica as RO-1.

In this optimization process, feed pressure was varied every one hour. One water sample was

collected for each feed pressure to analyze TDS, turbidity, hardness and silica. Other

important data such as flow rate, temperature, and outlet pressure were recorded as well

which is shown in Table B.6 of Appendix B.

The Figure 4.14 is the result from the optimization with different feed pressure.

0

0.5

1

1.5

2

0

200

400

600

800

1000

1200

0 60 120 180 240


TM

P (

bar

)

Flu

x (

LM

H)

Flux TMP

Once throughRecirculation

70

Figure 4.14 Flux and rejection of different feed pressure

According to this result, 12 bar of feed pressure was considered as the best condition of

second stage RO. It had the highest rejection rate of TDS, hardness, and silica compare the

other feed pressure.

e. Second stage RO with optimum condition

The optimum feed pressure from the optimization stage, 12 bar, was chosen to run the second

stage RO. For the first one hour, system was running under recirculation mode, then the rest

of the operation time, once through mode was taken place to take the permeate out.

Furthermore, feed salinity was measured hourly in order to see the development of salinity

in feed tank. Table B.7 in Appendix B is shown all experimental result of second stage RO.

Since water recovery rate 80% which was fixed, and volume of feed RO was 145 liters, so

permeate was 116 liters.

Figure 4.15 Flux and TMP of second stage RO at 12 bar

20

25

30

35

40

92

93

94

95

96

97

98

99

10 12 14 16 18

Flu

x (

LM

H)

Rej

ecti

on (

%)

Feed Pressure (bar)

% TDS % Hardness % Silica Flux

0

10

20

30

40

50

60

70

19

21

23

25

27

29

31

0 10 20 30 40 50 60 70 80 90

TM

P (

bar

)

Fee

d S

alin

ity (

mg/L

)

Flu

x (

LM

H)


Flux (LMH) TMP Feed Salinity (x100)

Recirculation Once through

71

As the result, average flux of second stage RO, 27 LMH, looked higher than that provided

by Hydranautic Projection Software (Figure E.4 in Appendix E). Moreover, salt rejection

was noticed only 88.16%, while hardness and silica rejection was higher than 90% which is

shown in Table 4.9.

Table 4.9 Result of RO-2 Experiment with Optimum Pressure

Parameter Unit Feed RO-2 Permeate RO-2 Reject RO-2 Rejection (%)

Appearance - Yellowish

and clear clear

Yellow and

slightly turbid -

Turbidity NTU 0.3 0.1 1.5 -

pH - 8.3 7.5 8.2 -

Conductivity µS/cm 2,650 314 10,440 -

TDS mg/L 1,723 204 6,786 88.16

P-Alkalinity mg/L as CaCO3 16 0 0 100

M-Alkalinity mg/L as CaCO3 230 22 1,160 90.43

Total Hardness mg/L as CaCO3 151.5 3.8 670 97.49

Ca Hardness mg/L as CaCO3 103 0 515 100

Chloride mg/L as Cl- 516.15 64.52 2,233 87.50

Silica mg/L as SiO2 8.94 0.73 42.01 91.83

4.2.3 Discussion

From the water recovery rate of each membrane unit of ZLD system which summarized in

Figure 4.16, total permeate from first stage RO (73 %) and second stage RO (15%) were

together 88 % of one cubic meter feed water. Final concentrate from second stage RO was

only 3.67% or only 36.7 liters of one cubic liters of feed. Therefore, only membrane base

system (MF and RO), more than 85% of water could be recovered which was higher than

one research of Lander (2013) about CTBD recycle, only 80%.

Figure 4.16 Percentage of RO permeate and other rejections

With the characteristic of first stage and second stage RO and its flow, final permeate

characteristic was shown in Table 4.10. Final TDS, hardness, and silica concentration were

only 60.67 mg/L, 7.37 mg/L and 6.10 mg/L respectively which was better than tap water or

Permeate RO-1

73%

Permeate RO-2

15%

Reject Ceramic

2%

Reject Duraflow

6%

Reject RO-2

4%

Permeate RO-1

Permeate RO-2

Reject Ceramic

Reject Duraflow

Reject RO-2

72

industrial water. Therefore, industry could recover a high quality of water, and that will bring

industry a lot of benefits such as saving money from operation and maintenance.

Table 4.10 Final Permeate Characteristic

Parameter Unit Permeate RO-1 Permeate RO-2 Final Permeate

Appearance - clear clear clear

Turbidity NTU <0.1 0.1 0.1

pH - 7.2 7.5 7.25

Conductivity µS/cm 58.2 314 100.83

TDS mg/L 32 204 60.67

P-Alkalinity mg/L as CaCO3 0 0 0.00

M-Alkalinity mg/L as CaCO3 10 22 12.00

Total Hardness mg/L as CaCO3 8.08 3.8 7.37

Calcium Hardness mg/L as CaCO3 2.08 0 1.73

Chloride mg/L as Cl- 6.95 64.52 16.55

Silica mg/L as SiO2 7.17 0.73 6.10

From the results of these pilot scale experiments, the proposed ZLD system for TPAC was

designed accordance with each membrane system’s performances data such as feed flow,

water recovery, average flux, feed pressure, and even chemical dosage.

4.3 System Engineering Design

Referring to water auditing result, 180 m3/day of wastewater was discharge from CTBD

treatment plant. However, due to CTBD treatment was running in batch mode operation, this

value might be different for some times of operation. Moreover, 180 m3/day of flow rate

was an average number which could be higher or lower than this. Since it was not the peak

flow value, it was not able to use as designed flow in system design, and need to multiply

with safety. Safety factor was an important factor which was unable to neglect in any system

designs, and it could affect both economic and safety of system.

In this case, safety factor was selected to be only 2 times of actual flow rate (audited flow

rate), and following were the main reasons of this selection:

Investment and O&M cost must be very high if system design with a higher safety

factor.

Avoid any shock flow or high flow rate from the drain pit of CTBD treatment plant.

Reserve for future expansion of CTBD treatment plant.

Hence, 360m3/day of design flow was selected. With this value, water recovery of whole

proposed ZLD system was designed to get a minimum 80% without considering of

dewatering process and crystallizer /evaporator. Meanwhile, 90%, 70%, 75%, and 85% of

water recovery were designed from Ceramic membrane system, First stage RO, Duraflow,

and Second stage RO, respectively. An overall system designed is demonstrated clearly in

Figure 4.17 below.

73

Figure 4.17 Overall system design

In addition, TDS concentration of both RO system was acquired from Hydranautic

Projection Software while Ceramic MF and Duraflow system was acquired from pilot

experiment with real wastewater from TPAC. Salt balance of ZLD system, which was shown

in Figure 4.18, was also figured out in order to evaluate whether this system was running in

a good condition and performance or not by calculating the percentage of accuracy.

Figure 4.18 Salt balance of proposed ZLD system

5.43% of percentage of accuracy was showing that this proposed ZLD system will be

running functionally without any concerns. The detail designed plan of proposed ZLD

system in TPAC is shown in Figure 4.19 which provided detail information of system,

pumps, and other instruments which utilized in proposed ZLD system.

- % 1

(1

00%

53.72 145.38)

153.100

5.43%

72

OutputAccuracy

Input

Input

74

Holding tank-1

10 m3 CMF Per. Tank/BW

Tank, 6 m3

pH pH pH

Discharge Sump

5m3

To Discharge sump

To Discharge Sump

To Discharge Sump

To Discharge Sump

To Cooling Tower Basin

Wastewater from CTBD

treatment plant

360m3/d

RFM

RFM

RFM

PG

PG

PGPG

PG

PG

PG

PG

PG

Conc. Recirculation

CIP Tank(500L)

CMF Feed Pump

CMF CP

Conc. CIP Return

RFMPermeate CIP Return

BW Pump

RO-1 HPP

RO-1 Prefilter

RO-1 Reject

RO-1 Permeate

Conc. CIP Return

Permeate CIP Return

Antiscale

(200L)HCl Tank

(200L)

CIP Tank

(1000L)

: Check Valve (CV)

Legend:

: Butterfly Valve (BFV)

: Ball valve (BV)

: Joint expansion

: In-line mixer

: Sampling valve (SV)

: Pump

: pH meter

: Pressure gauge

: Rota meter flow

: Magnetic paddle (mixer)

: High pressure pump

: Ceramic MF membrane

: Duraflow MF membrane

: Backwash

pH

PG

RFM

M

RO-1 Permeate

NaOH

(200L)

Mixing tank-1

6 m3

Mixing tank-2

6 m3

Mixing tank-3

6 m3

Concentration tank

6 m3

CIP tank

(500L)

Neutralization tank

6 m3

HCl(200L)

RO-2 feed tank

6 m3

RO water tank

10 m3

Slurry return Permeate

DFMF Feed

Pump

HPP

CMF

DFMF

BW

M-1 M-2 M-3 M-4

Conc. C

IP R

etu

rn

Permeate CIP Return

RO-2 HPP

Conc. CIP Return

Permeate CIP Return

Permeate

Conc. Recirculation

RO-2 reject

Supply pump

FS

: Flow senserFS

FS

FS

FS

FS+CS

FS

FS+CS

FS+CS

FS+CS

FS+CS

FS+CS

FS+CS

: Conductivity senserCS

: Level senserLS

LS

LS

LS

LS

LS LS LS LS LS

LS

Size: A3Scale: None

DWN: Mov Chimeng

Date: 01/Feb/2014

Title:ZLD System (2 stages RO)

Capacity 360m3/d

Asian Institute of Technology

Liquid Purification Engineering

Project: Thai Polyacetal Co., Ltd. (TPAC)

Slurry Pump

Slurry remove

PG

PG

RO water

RO water

RO water

Na2CO3

(100L)

MgO

(1000L)

RFM

PG

RFM

RFM

RFM

RFM

: Chemical pump

RFM

Clean-outClean-outClean-out

CMF Feed Pump

Cap. : 15 m3/h

@20m

Duty : 1 duty

Model : CR20-3

CMF Circulation Pump

Cap. : 75 m3/h

@50m

Duty : 1 duty

Model : CR90-4

CMF Backwash Pump

Cap. : 25 m3/h

@20m

Duty : 1 duty

Model : CR32-2

RO-1 & 2 Feed Pump

Cap. : 30 m3/h

@ 20m

Duty : 2 duty

Model : CR32-4

RO Prefilter

Cap. : 15 m3/h

@ 5 micron

Duty : 2 duty

RO-1 High Pressure Pump

Cap. : 30 m3/h @ 100mDuty : 1 duty

Model : CR32-9

DFMF Feed Pump

Cap. : 60 m3/h @30m

Duty : 2 duty, 1 stand-by

Model : CRN64-2

Slurry Pump

Cap. : 5 m3/h @20m

Duty : 1 duty

Model : CR5-6

Chemical Pump

Cap. : 18.2L/min @86m

Duty : 6 duty

Model : Wilden P25

CIP Pump

Cap. : 25 m3/h @20m

Duty : 4 duty

Model : CRN32-2

RO-2 High Pressure Pump

Cap. : 15 m3/h @120m

Duty : 1 dutyModel : CR15-14

RO Water Supply Pump

Cap. : 20 m3/h @40m

Duty : 1 dutyModel : CR20-5

CMF Membrane and Housing

Ele. : Ø30mm x1016mm x19ch

No : 32 ele./housing

Qnty : 192 pcs

Type : TubularDuty : 5 housings duty,

1 housing stand-by

Duraflow MF Membrane

Ele. : Ø15cm x183cm x10 cha

No : 4 ele./skid

Qnty : 12 pcs

Type : Tubular

Duty : 2 skids duty,1 skid stand-by

RO-1 Membrane and Housing

Ele. : Ø20.32cm x1016mm

No : 6 ele./housing

Qnty : 30 pcs

Type : Spiral Wound

Duty : 3 housings duty,

2 housing stand-by

RO-2 Membrane and Housing

Ele. : Ø20.32cm x1016mm

No : 6 ele./housing

Qnty : 24 pcs

Type : Spiral Wound

Duty : 2 housings duty,

2 housing stand-by

PG

Discharge

Pump

PG

FS

PG

FS

PG

RO-1 Prefilter

RO-1

Feed Pump

RO-2

Feed Pump

RFM

RO CIP Unit (For RO-1 and RO-2)

RFM

Antiscale

(200L)HCl Tank

(200L)

CIP Tank

(1000L)

RO water

RO CIP Unit (For RO-1 and RO-2)

Discharge PumpCap. : 20 m3/h @40m

Duty : 1 duty

Model : CR20-5

PG

PG

PG

PG

Figure 4.19 Plan diagram of proposed ZLD system

75

4.4 Cost Information

Table 4.11 below demonstrates both investment cost, operation and maintenance cost of each

major system which was estimated and provided by LPE. From this table, Ceramic MF system

alone occupied nearly 50% of total investment cost of system. It also costs double of RO

systems and Duraflow system (with chemical treatment) combined. Hence, it would be better

to replace ceramic membrane MF with hollow fiber MF in order to decrease investment cost.

Moreover, cost for control panel, accessories and power cable also contributed as major part of

cost information due to automatically control of membrane system was simply necessary.

However, operation and maintenance (O&M) cost of Duraflow system with chemical

precipitation was the highest compared to other system due to chemicals consumption

(Magnesium oxide, Sodium carbonate, Hydrochloric acid, and Sodium hydroxide) in chemical

precipitation. All operation and maintenance cost was included chemical consumption cost,

membrane replacement cost, power cost, and maintenance cost for whole year round.

Table 4.11 Cost Information of Major System

Equipment Investment Cost

(THB)

O&M Cost (THB)

Per year Per day

Ceramic MF system 12,215,900 1,035,800 2,838

RO system (Both RO-1 and RO-2) 3,331,600 452,700 1,240

Duraflow MF system with chemical

precipitation 3,828,900 3,029,000 8,300

Pipes 149,400

738,000 2,022 Installation and Labor cost 511,200

Skid and Accessories 5,899,300

Control Panel and Power cable 2,500,000

Total: 28,436,300 5,255,500 14,400

According to O&M cost from Table 4.10, which was estimated with 360 m3/d of designed flow,

the cost of treatment per cubic meter of wastewater daily was calculated 40 baht/m3 of

wastewater. On the other hand, currently TPAC was paying around only 30 baht/m3 on

industrial water to use in cooling tower. This price was included the discharge price as well.

The treatment cost of proposed ZLD system was more expensive than the current situation,

which TPAC need to pay, 10 baht/m3.

As the matter of fact, ZLD system still became more and more attractive from many industries

for many reasons and solution to reduce the cost. Strict regulation in future which will be able

to force industries not to discharge wastewater or in high price is the main advantage for ZLD

system. Besides, ZLD could solve water scarcity in critical condition like industrial water was

limited from supplier, etc. Also, further study of ceramic membrane system and chemical

precipitation would be a huge reduction of investment and treatment cost. One more important

thing about ZLD was improving cooling system and cooling tower performance. Due to high

quality of RO system permeate, cooling tower could be performed well with higher cycle of

concentration. Substantial amount of water could be saved, even maintenance cost of cooling

tower as well. All of these points are the potential advantages for industry to accept ZLD

system.

76

Chapter 5

Conclusions and Recommendations

5.1 Conclusion

This study mainly focused on membrane based Zero Liquid Discharge (ZLD) system in

petrochemical industry’s cooling tower blowdown. To better understand the privilege

situation, water auditing of CTBD treatment plant was done which showed that large amount

of wastewater were discharged from CTBD treatment plant every day. A two stage pilot

scale RO system of ZLD system were designed along with respectively pretreatment system

to recover wastewater from CTBD treatment plant. However, evaporator and dewatering

process were exempted in this research; thus 85% water recovery was achievable. According

to pilot scale experiment of ZLD system, a detail proposed ZLD system (engineering design)

was designed, and cost information was also estimated.

Therefore, a summary and conclusion of important findings from this study are following:

1. On a daily basis, wastewater from CTBD treatment plant ~180m3 ±10 with high

silica, hardness and TDS was discharged to the drain pit and finally pumped out of

industry without further treatment.

2. Water and salt balance of CTBD treatment plant were conducted during water

auditing. As per calculation, the percentage of accuracy between input and output of

both water and salt balance were calculated to be 28.40% and 28.35% respectively,

less than 30%. These results demonstrated that no serious problem in plant operation

or any leakages was happened. Anyway, many possible causes of this differences

could be figured out such as: average number of collected data, water remaining in

system, inaccuracy of data reading, and batch mode operation of system.

3. Pilot scale experiment of ZLD system was designed with two stages of RO system

where one cubic meter of real wastewater collected from drain pit of CTBD treatment

plant was used. Each stage of RO system equipped with different kind of

pretreatment system: Ceramic membrane for first stage RO; and Duraflow MF with

chemical precipitation for second stage RO.

4. Bench test of chemical precipitation was done with 9 samples with variation of soda

ash and magnesium oxide dosage. As the result, 50mg/L of soda ash and 3000mg/L

of magnesium oxide were selected as the optimum dosage in term of silica removal.

5. Ceramic MF and Duraflow MF performed well as RO pretreatment due to permeate

of both MF met the criteria and requirement of RO feed. Permeate turbidity of both

MF were observed to be less than 1 NTU.

6. Chemical precipitation with Duraflow MF, large portion of hardness and silica

concentration were removed, 74.58% and 94.74% respectively. It was a significant

removal rate which Duraflow MF or other MF only could not accomplish. It also

revealed that chemical precipitation with Duraflow MF is an effective system in

hardness and silica reduction.

77

7. By varying feed pressure and using rejection as key tools in optimization evaluation,

8 bar and 12 bar of feed pressure was observed to be the optimum condition for first

and second stage RO, respectively.

8. Due to differences of feed characteristic, rejection rate of second stage was better

than that of the first stage in term of hardness and silica. However, there were contrast

for salt rejection where first stage of RO rejection was higher (Table 4.5 and 4.8).

9. According to experimental result, total amount of permeate water which possibly

recover back to cooling tower was more than 85%, while only less than 4% was the

final concentrate from second stage RO.

10. The final TDS, hardness and silica concentration after mixing of permeate from both

stages RO were 60.67mg/L, 7.37mg/L as Ca2CO3, and 6.10mg/L, respectively.

11. Cost estimation of proposed ZLD system, ceramic MF membrane system alone

occupied nearly 50% of total investment cost, and it was double of the cost

combination of RO system and Duraflow system with chemical treatment.

Installation and labor cost, skid and accessories, control panel, and power cable were

also contributed large amount of investment cost.

12. Due to chemical usage in chemical precipitation, it contributed more than 50% of

total O&M cost. Likewise, ceramic MF system O&M cost was also very high which

was twice times of RO systems (two stages RO). Due to the high replacement cost

of ceramic membrane skid and accessories.

13. Treatment cost per cubic meter of proposed ZLD system was estimated to be 40

baht/m3 which was 10 baht/m3 more expensive than the current situation of water

usage in TPAC. Presently, TPAC pays only 30 baht/m3 for industrial water which

included discharge price.

14. In spite of this higher investment cost and even higher treatment cost, ZLD system

are still considered as a capable technology for industries in term of water

reclamation due to many driving forces like: future strict effluent regulation, water

scarcity in the world, corporate social responsibility, etc. Moreover, cooling system

and cooling tower, which utilized high quality of permeate from RO system, could

perform better than using industrial water which has a lower quality. Besides, further

study on pretreatment system like ceramic membrane and chemical precipitation

must bring down substantial amount of investment and O&M cost as well. At the end

of the day, ZLD system will become more and more attractive system for water reuse

and recovery from many sectors.

5.2 Recommendation for Further Research

According to the result of research experiment, the following recommendations are proposed

for further research:

1. In this study, concentrate of ceramic system and Duraflow MF system was not

included in consideration of ZLD system, and it was simply discharged from system.

78

Therefore, it should be considered and further sent to dewatering process in next

study in order to recover more and more water to achieve zero liquid discharge.

2. Final concentrate of second stage RO, high TDS content, could be further

concentrated with seawater RO membrane, or directly sent to evaporator and

crystallizer system. Permeate or distillate from these process could be recovered back

to system for reusing.

3. With the intention of reducing the investment cost and O&M cost of system, ceramic

membrane system should be replaced by hollow fiber membrane. However many

disadvantages of this kind of membrane (hollow fiber) such as easily damage and

system complication might be an obstacle, and need to be assessed careful for future

studies.

4. Removal rate in chemical precipitation (cold lime softening) was not very high due

to operating temperature. Therefore, in order to have higher removal rate with a low

dosage of chemical used, warm lime softening or hot lime softening should be taken

place instead of cold lime softening. However, it would be easy if raw wastewater

had high temperature, for example 45oC of water from process. If not, operational

cost for heating water will be significantly increased. This section is recommended

for further research and study with different chemical types and dosage in order to

decrease operation cost.

5. Since nitrogen removal was not included in this study, it should be considered as the

main parameter for next study in order to find out its contribution to unpleasant

biological growth in cooling tower and cooling system. Nitrogen cycle and nitrogen

balance of system could be a major tool as well in cooling system control.

79

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83

Appendix A

Research and Experimental Activities

84

Figure A.1 Product gallery of TPAC

Figure A.2 Cooling Tower of TPAC

85

Figure A.3 CTBD treatment plant in TPAC

Figure A.4 Sampling and water samples

86

Figure A.5 Ceramic membrane pilot unit

Figure A.6 Duraflow MF pilot unit

Ceramic membrane

pilot unit

Feed tank (1m3) Permeate tank

Feed tank

Feed tank

Feed Permeate

Membrane house

87

Figure A.7 Reverse osmosis pilot unit

Figure A.8 Bench test of chemical precipitation

Membrane house

Feed tank

Permeate tank Prefilter High pressure

pump

Magnetic stirurer

Beaker (1L)

88

Appendix B

Experimental Result

89

Table B.1 Result of Ceramic Membrane Pilot Test at 32 oC

Time (min) Flow (LPH)

Flux (LMH) Turbidity (NTU)

Feed Permeate Permeate Feed

0 2080 180 818.18 0.85 1.7

10 2070 170 772.73 - -

20 2050 150 681.82 - -

30 2040 140 636.36 - -

40 2032 132 600.00 - -

50 2025 125 568.18 - -

60 2020 120 545.45 0.12 4.18

70 2020 120 545.45 - -

80 2018 118 536.36 - -

90 2015 115 522.73 - -

100 2012 112 509.09 - -

110 2010 110 500.00 - -

120 2008 108 490.91 0.09 4.59

130 2005 105 477.27 - -

140 2005 105 477.27 - -

150 2003 103 468.18 - -

160 2001 101 459.09 - -

170 2000 100 454.55 - -

180 1999 99 450.00 0.14 6.13

190 1998 98 445.45 - -

200 1997 97 440.91 - -

210 1996 96 436.36 - -

220 1995 95 431.82 - -

230 1994 94 427.27 - -

240 1993 93 422.73 0.11 7.02

250 1992 92 418.18 - -

260 1991 91 413.64 - -

270 1990 90 409.09 - -

280 1990 90 409.09 - -

290 1990 90 409.09 - -

300 1990 90 409.09 0.07 7.91

310 1990 90 409.09 - -

320 1990 90 409.09 - -

330 1989 89 404.55 - -

340 1989 89 404.55 - -

350 1989 89 404.55 - -

90

Time (min) Flow (LPH)

Flux (LMH) Turbidity (NTU)

Feed Permeate Permeate Feed

360 1989 89 404.55 0.07 8.81

370 1989 89 404.55 - -

380 1988 88 400.00 - -

390 1988 88 400.00 - -

400 1988 88 400.00 - -

410 1988 88 400.00 - -

420 1987 87 395.45 0.06 9.61

430 1987 87 395.45 - -

440 1987 87 395.45 - -

450 1987 87 395.45 - -

460 1987 87 395.45 - -

470 1987 87 395.45 - -

480 1987 87 395.45 0.08 11.5

Average 465.21 0.18 6.83

Note: Feed pressure was fixed: 3 bar

Concentrate pressure: 1.3 bar (constant)

Tran-membrane pressure: 2.15 bar (constant)

Concentrate flow: 1900 L/h (constant)

91

Table B.2 Result of First Stage RO Optimization

Time

(min)

Temp

(oC)

Flow (LPH) Pressure (bar)

Flux

(LMH)

TMP

(bar) TCF

Normalized

Flux (LMH)

Water

recovery

(%)

Permeate Quality

Feed Conc. Per. Feed Conc. TDS

(mg/L)

Turbidity

(NTU)

Hardness

(mg/L as

CaCO3)

Silica

(mg/L

as SiO2)

0 28 880 750 130

6 2

16.46

4

0.9137 15.03 14.77

20.5 <0.1 2.63 5.61

10 29 870 740 130 16.46 0.8869 14.59 14.94

20 30 865 730 135 17.09 0.8611 14.72 15.61

30 30 865 730 135 17.09 0.8611 14.72 15.61

40 31 870 730 140 17.72 0.8363 14.82 16.09

50 31 870 730 140 17.72 0.8363 14.82 16.09

60 31 870 730 140 17.72 0.8363 14.82 16.09

70 31.5 825 625 200

8 5

25.32

6.5

0.8241 20.86 24.24

16.5 <0.1 2.42 4.54

80 31.5 840 640 200 25.32 0.8241 20.86 23.81

90 31.5 840 640 200 25.32 0.8241 20.86 23.81

100 32 845 640 205 25.95 0.8123 21.08 24.26

110 32 850 645 205 25.95 0.8123 21.08 24.12

120 32 850 645 205 25.95 0.8123 21.08 24.12

130 32 810 555 255

10 7

32.28

8.5

0.8123 26.22 31.48

16.5 <0.1 2.02 4.4

140 32 810 555 255 32.28 0.8123 26.22 31.48

150 32 810 555 255 32.28 0.8123 26.22 31.48

160 32 810 555 255 32.28 0.8123 26.22 31.48

170 32 810 555 255 32.28 0.8123 26.22 31.48

180 32 810 555 255 32.28 0.8123 26.22 31.48

190 32.5 780 480 300

12 9

37.97

10.5

0.8006 30.40 38.46

17.4 <0.1 2.42 4.55

200 32.5 780 480 300 37.97 0.8006 30.40 38.46

210 32.5 780 480 300 37.97 0.8006 30.40 38.46

220 32.5 780 480 300 37.97 0.8006 30.40 38.46

230 32.5 780 480 300 37.97 0.8006 30.40 38.46

240 32.5 780 480 300 37.97 0.8006 30.40 38.46

250 32.5 730 380 350

15 13

44.30

14

0.8006 35.47 47.95

21.9 <0.1 2.63 5.22

260 32.5 730 380 350 44.30 0.8006 35.47 47.95

270 32.5 730 380 350 44.30 0.8006 35.47 47.95

280 32.5 730 380 350 44.30 0.8006 35.47 47.95

290 32.5 730 380 350 44.30 0.8006 35.47 47.95

300 32.5 730 380 350 44.30 0.8006 35.47 47.95

92

Table B.3 Result of Optimized First Stage RO at 8 bar Feed Pressure

Time

(min

)

Temp.

(oC)

Flow (LPH) Flux

(LMH

)

TCF

Normalized

Flux

(LMH)

Water

Recovery

(%)

Feed

Salinity

(mg/L) Feed Conc Per

0 29 845 640 205 25.95 0.8869 23.01 24.26 435.5

10 28.5 830 630 200 25.32 0.9002 22.79 24.10 -

20 28 825 635 190 24.05 0.9137 21.97 23.03 -

30 28 830 640 190 24.05 0.9137 21.97 22.89 -

40 28 800 610 190 24.05 0.9137 21.97 23.75 -

50 28 795 610 185 23.42 0.9137 21.40 23.27 -

60 28 795 610 185 23.42 0.9137 21.40 23.27 595.3

70 28 795 610 185 23.42 0.9137 21.40 23.27 -

80 28 795 610 185 23.42 0.9137 21.40 23.27 -

90 28.5 795 610 185 23.42 0.9002 21.08 23.27 -

100 28.5 790 605 185 23.42 0.9002 21.08 23.42 -

110 28.5 790 605 185 23.42 0.9002 21.08 23.42 -

120 28.5 795 610 185 23.42 0.9002 21.08 23.27 729.5

130 29 800 620 180 22.78 0.8869 20.21 22.50 -

140 29 800 620 180 22.78 0.8869 20.21 22.50 -

150 29 800 620 180 22.78 0.8869 20.21 22.50 -

160 29 800 620 180 22.78 0.8869 20.21 22.50 -

170 29 800 625 175 22.15 0.8869 19.65 21.88 -

180 29 805 630 175 22.15 0.8869 19.65 21.74 1013.3

190 29.5 810 640 170 21.52 0.8739 18.81 20.99 -

200 29.5 815 645 170 21.52 0.8739 18.81 20.86 -

210 29.5 815 650 165 20.89 0.8739 18.25 20.25 -

220 30 815 650 165 20.89 0.8611 17.99 20.25 -

230 30 815 655 160 20.25 0.8611 17.44 19.63 -

240 30 810 655 155 19.62 0.8611 16.90 19.14 1372.6

250 30 820 670 150 18.99 0.8611 16.35 18.29 -

260 30 820 670 150 18.99 0.8611 16.35 18.29 1443

Average 20.10 22.07


Concentrate pressure: 5 bar (constant)


93

Table B.4 Result of Chemical Precipitation Optimization with MgO and Na2CO3

Test

No

Vol.

Sample

(mL)

Chemical Dosage

(mg/L) Vol. NaOH (mL)

Conduct

(µS/cm) pH

Hardness (mg/L as

CaCO3) Alkalinity (mg/L)

Silica

(mg/L) Na2CO3 MgO pH=9 pH=11

Total

Hardness

Ca.

Hardness P M

1

500 50 1000 1.2 5.5 2880 10.67 166.65 161.2 380 340 53.92

500 50 1000 1.2 5.5 2900 10.6 161.6 156 370 330 55.74

500 50 1000 1.2 5.5 2890 10.7 169.18 166.4 390 340 51.95

Average 1.2 5.50 2890 10.66 165.81 161.2 380 336.67 53.87

2

500 50 2000 0.5 4.5 2900 10.65 161.6 156 375 315 39.73

500 50 2000 0.5 4.5 3000 10.6 164.13 150.8 385 315 40.51

500 50 2000 0.5 4.5 2810 10.75 159.08 166.4 370 320 38.32

Average 0.5 4.50 2903 10.67 161.60 157.73 376.67 316.67 39.52

3

500 50 3000 0 5 2750 10.54 159.08 143 315 310 29.07

500 50 3000 0 5 2800 10.61 161.6 150.8 330 320 30.09

500 50 3000 0 5 2700 10.5 159.08 143 310 300 28.93

Average 0 5 2750 10.55 159.92 145.6 318.33 310 29.36

4

500 150 1000 0.8 5.2 2880 10.64 171.7 166.4 480 355 67.64

500 150 1000 0.8 5.2 3010 10.62 171.7 161.2 470 345 64.38

500 150 1000 0.8 5.2 2750 10.7 171.7 166.4 500 360 69.01

Average 0.8 5.2 2880 10.65 171.7 164.67 483.33 353.33 67.01

5

500 150 2000 0.3 5 3070 10.72 171.7 150.8 430 380 46.03

500 150 2000 0.3 5 3010 10.68 166.65 156 410 355 45.34

500 150 2000 0.3 5 3100 10.77 166.65 150.8 420 410 47.8

Average 0.3 5 3060 10.72 168.33 152.53 420 381.67 46.39

94

Test

No

Vol.

Sample

(mL)

Chemical Dosage

(mg/L) Vol. NaOH (mL)

Conduct

(µS/cm) pH

Hardness (mg/L as

CaCO3) Alkalinity (mg/L) Silica

(mg/L)

MgO Na2CO3 MgO pH=9 pH=11 Total

Hardness

Ca.

Hardness P

Na2C

O3

6

500 150 3000 0 5.2 2930 10.5 156.55 161.2 385 365 31.35

500 150 3000 0 5.2 3000 10.6 161.6 155 370 345 32.53

500 150 3000 0 5.2 2900 10.55 156.55 151.55 380 375 31.01

Average 0 5.2 2943 10.55 158.23 155.92 378.33 361.67 31.63

7

500 250 1000 0 5.3 3120 10.7 166.65 150.8 450 410 64.11

500 250 1000 0 5.3 3000 10.65 171.7 156 460 400 64.38

500 250 1000 0 5.3 3250 10.71 161.6 150.8 430 390 65.01

Average 0 5.3 3123 10.69 166.65 152.53 446.67 400 64.5

8

500 250 2000 0 6.5 3100 10.81 166.65 161.2 480 375 43.37

500 250 2000 0 6.5 3120 10.76 171.7 166.4 470 360 45.12

500 250 2000 0 6.5 3020 10.8 161.6 156 475 390 41.43

Average 0 6.5 3080 10.79 166.65 161.2 475 375 43.31

9

500 250 3000 0 6.5 3070 10.83 166.65 156.55 470 375 37.71

500 250 3000 0 6.5 3100 10.81 171.7 150.8 450 390 36.27

500 250 3000 0 6.5 3030 10.85 166.65 161.2 485 325 38.47

Average 0 6.5 3067 10.83 168.33 156.18 468.33 363.33 37.48

Note: One normality of NaOH was used to adjust pH in bench test.

95

Table B.5 Result of Duraflow MF at 2 bar Feed Pressure

Time (min) Temperature (oC) Flow (LPH)

Flux (LMH) Permeate Concentrate

0 30.2 300 7900 1071.43

10 30.2 180 8020 642.86

20 31.5 140 8060 500.00

30 31.5 120 8080 428.57

40 31.7 105 8095 375.00

50 31.8 100 8100 357.14

60 31.8 96 8104 342.86

70 32 95 8105 339.29

80 32.2 94 8106 335.71

90 32.1 92 8108 328.57

100 32.1 90 8110 321.43

110 32 89 8111 317.86

120 32 89 8111 317.86

130 32 88 8112 314.29

140 32.1 86 8114 307.14

150 32.1 85 8115 303.57

160 32.1 81 8119 289.29

170 31.7 78 8122 278.57

180 31.6 75 8125 267.86

190 31.6 73 8127 260.71

200 31.5 70 8130 250.00

210 31.5 67 8133 239.29

220 31.5 55 8145 196.43

Average 364.60


Concentrate pressure: 0.75 bar (constant)


Feed flow: 8,200 L/h (constant)

96

Table B.6 Result of Second Stage RO Optimization

Time

(min)

Temp.

(oC)

Flow (LPH) Pressure (bar) Flux

(LMH)

TMP

(bar) TCF

Normalized

Flux

(LMH)

Water

Recovery

(%)

Permeate Quality

Feed Conc Per Feed Conc TDS

(mg/L)

Turbidity

(NTU)

Hardness

(mg/L as

CaCO3)

Silica

(mg/L as

SiO2)

0 27.5 810 600 210

10 7.5

26.58

8.75

0.9274 24.65 25.93

118.89 0.5 3.43 0.534

10 28.5 795 580 215 27.22 0.9002 24.50 27.04

20 29 765 550 215 27.22 0.8869 24.14 28.10

30 30 750 530 220 27.85 0.8611 23.98 29.33

40 30.5 740 520 220 27.85 0.8486 23.63 29.73

50 31 750 530 220 27.85 0.8363 23.29 29.33

60 31 750 530 220 27.85 0.8363 23.29 29.33

70 31.5 730 455 275

12 10

34.81

11

0.8241 28.69 37.67

103.03 0.48 2.63 0.517

80 31.5 730 455 275 34.81 0.8241 28.69 37.67

90 31.5 730 455 275 34.81 0.8241 28.69 37.67

100 31.5 735 460 275 34.81 0.8241 28.69 37.41

110 32 735 460 275 34.81 0.8123 28.27 37.41

120 32 735 460 275 34.81 0.8123 28.27 37.41

130 32.5 730 410 320

14 12

40.51

13

0.8006 32.43 43.84

113.75 0.59 3.23 0.540

140 33.5 725 400 325 41.14 0.7778 32.00 44.83

150 34 725 400 325 41.14 0.7667 31.54 44.83

160 33 725 405 320 40.51 0.7891 31.96 44.14

170 33 725 405 320 40.51 0.7891 31.96 44.14

180 33 725 405 320 40.51 0.7891 31.96 44.14

190 32.5 705 350 355

16 14

44.94

15

0.8006 35.97 50.35

121.75 0.37 3.03 0.574

200 32.5 705 350 355 44.94 0.8006 35.97 50.35

210 32.5 705 350 355 44.94 0.8006 35.97 50.35

220 32.5 705 350 355 44.94 0.8006 35.97 50.35

230 32.5 705 350 355 44.94 0.8006 35.97 50.35

240 32.5 705 350 355 44.94 0.8006 35.97 50.35

250 32.5 700 305 395

18 16

50.00

17

0.8006 40.03 56.43

133.9 0.47 5.45 0.563

260 32.5 700 305 395 50.00 0.8006 40.03 56.43

270 33 710 315 395 50.00 0.7891 39.45 55.63

280 33 710 315 395 50.00 0.7891 39.45 55.63

290 33 710 315 395 50.00 0.7891 39.45 55.63

300 33 710 315 395 50.00 0.7891 39.45 55.63

97

Table B.7 Result of Optimized Second Stage RO at 12 bar Feed Pressure

Time

(min)

Temp

(oC)

Flow (LPH) Flux

(LMH) TCF

Normalized

Flux (LMH)

Water

Recovery

(%)

Feed

Salinity

(mg/L) Feed Conc Per

0 28.5 765 500 265 33.54 0.9002 30.20 34.64 1,723

10 30 750 480 270 34.18 0.8611 29.43 36.00 1,723

20 31 775 500 275 34.81 0.8363 29.11 35.48 1,723

30 31 745 470 275 34.81 0.8363 29.11 36.91 1,723

40 31 735 460 275 34.81 0.8363 29.11 37.41 1,723

50 31 735 460 275 34.81 0.8363 29.11 37.41 1,723

60 31.5 735 460 275 34.81 0.8241 28.69 37.41 2,425

70 29 750 500 250 31.65 0.8869 28.07 33.33 3,107

80 29 760 540 220 27.85 0.8869 24.70 28.95 4,414

90 29.5 760 580 180 22.78 0.8739 19.91 23.68 6,786

Average 27.74 34.12


Concentrate pressure: 10 bar (constant)

Tran-membrane pressure: 11 bar (constant)

98

Table B.8 Summary of Analytical Result of Whole ZLD System

Parameter Unit

Ceramic RO-1 Duraflow RO-2

Feed Permeate Feed Permeate Reject Feed

Permeate

(before

neutral)

Permeate

(after

neutral)

Feed Permeate Reject

Appearance - Slightly

Turbid

Slightly

yellow

Slightly

yellow Clear

Yellow

and

slightly

turbid

Yellow

and

slightly

turbid

Yellowish

and clear

Yellowish

and clear

Yellowish

and clear Clear

Yellow

and

slightly

turbid

Turbidity NTU 1.7 0.18 0.18 <0.1 1.4 1.4 0.3 0.3 0.3 0.1 1.5

pH (at 250C) - 7.9 7.6 7.6 7.2 8.14 8.14 11.02 8.35 8.3 7.5 8.2

Conductivity μS.cm-1 657 670 670 58.2 2,220 2,220 2,670 2650 2,650 314 10,440

TDS mg/L 427 435.5 435.5 32 1,443 1,443 1,736 1723 1,723 204 6,786

P- Alkalinity mg/L as

CaCO3 Nil 0 0 0 0 0 - 16 16 0 0

M-

Alkalinity

mg/L as

CaCO3 115 125 125 10 450 450 - 230 230 22 1,160

Total

Hardness

mg/L as

CaCO3 156.55 151.5 151.5 8.08 595.9 595.9 152.67 151.5 151.5 3.8 670

Calcium

Hardness

mg/L as

CaCO3 109.2 104 104 2.08 405.6 405.6 - 103 103 0 515

Chloride mg/L as

Cl- 86.85 84.37 84.37 6.95 307.71 307.71 - 516.15 516.15 64.52 2,233

Sulfate mg/L as

SO4-2

38.18 - - - - - - 175.54 175.54 0.15 774.12

Silica mg/L as

SiO2 43.63 43.63 43.63 7.17 170.04 170.04 8.95 8.94 8.94 0.73 42.01

Free

Chlorine

mg/L as

Cl2 0.01 0.01 0.01 - - - - 0.07 0.07 - -

99

Appendix C

Case Studies from Internship in LPE

100

Case #1: Sugar Removal from Orange Juice

I. General Information

1. Test detail

Feed water source : Orange Juice from Malee Sampran Public Company Limited

Testing date : December 24-25, 2013

Process : Microfiltration (MF)

Nanofiltration (NF)

Membrane type : Ceramic Microfiltration (0.2 µm), filtration area 0.22m2

Polymeric Nanofiltration (1,000 Daltons of MWCO), filtration

area 6.97m2

Test site : LPE Workshop

2. Objective of the test

The test was done to observe the possibility of membrane filtration process for reducing the

sugar content in orange juice by using microfiltration for clarification and then separate sugar

by using nanofiltration system. Moreover, further study on MF retentate, permeate and

retentate of NF test will be conducted by Malee Sampran Public Company Limited after this

pilot experiment. The pilot test objective are listed as following:

- Remove suspended and most of colloidal solids from orange juice by MF process.

- Reduce the sugar from MF Permeate (clear orange juice) by NF process.

II. Test Procedure

This pilot test was divided into two processes: Microfiltration process (ceramic membrane)

and Nanofiltration process to separate sugar. The brief flow diagram of experiment is

presented in Figure C.1.

Figure C.1 Flow diagram of sugar removal processes

101

1. Microfiltration process

- Feed tank of MF pilot unit was filled by orange juice sample.

- Start pilot unit by re-circulation retentate back to feed tank, collect permeate water

in separated tank.

- Record operation data every 20 minutes.

- Run pilot unit by controlling the maximum temperature of feed at 22oC until sample

had finished.

- Collect sample from Feed, permeate, and retentate.

- Analyze orange juice sample with following parameter

o pH , Turbidity, Brix and Conductivity

Figure C.2 Ceramic MF pilot unit (left) and NF pilot unit (right)

2. Nanofiltration process

- Fill MF permeate to NF pilot unit feed tank.

- Start pilot unit NF test by re-circulation retentate back to feed tank, collect permeate

sample in separated tank.

- Record operation data every 5 minutes.

- Run test unit by controlling the maximum temperature of feed at 22oC until sample

had finished.

- Collect orange juice sample from permeate and retentate.

- Analyze orange juice sample with following parameter:

o pH, Turbidity, Brix and Conductivity

III. Result

1. Operation data of MF

110 liters of water sample (orange juice) was fed to feed tank, and 66 liters was collected at

the permeate side of pilot unit while the rest 44 liters was MF retentate. Thus, total water

102

recovery of this process was calculated around 60%. Moreover, all of result and operation

data are illustrated in Table C.1 and Figure C.3

Table C.1 Operation Data of MF Process at 2.76 bar Feed Pressure

Time Flow (L/h) Brix Conc. (%) Temp.

(oC)

Flux

(LMH) Permeate Feed Permeate Feed

0 10.26 2510.26 12.4 13 14 46.64

20 10.26 2510.26 12.4 13 18 46.64

40 10.26 2510.26 12.4 13 21 46.64

60 9.18 2509.18 12.4 13 19 41.73

80 8.46 2508.46 12.6 13 18 38.45

100 8.28 2508.28 12.6 13 18 37.64

120 7.74 2507.74 12.6 13 18 35.18

140 7.74 2507.74 12.6 13 19 35.18

160 7.38 2507.38 12.6 13 20 33.55

180 7.02 2507.02 12.6 13 19 31.91

200 6.84 2506.84 12.6 13 20 31.09

220 6.3 2506.3 12.6 13.4 20 28.64

240 6.3 2506.3 12.6 13.4 20 28.64

260 6.3 2506.3 12.6 13.4 21 28.64

280 5.94 2505.94 12.6 13.4 20 27.00

300 7.2 2507.2 12.8 13.4 20 32.73

320 6.66 2506.66 12.8 13.4 21 30.27

340 5.76 2505.76 12.6 13.4 20 26.18

360 6.84 2506.84 12.8 13.4 21 31.09

380 5.76 2505.76 12.8 13.4 21 26.18

400 7.56 2507.56 12.8 13.4 20 34.36

420 5.4 2505.4 12.8 13.4 20 24.55

440 5.94 2505.94 12.8 13.4 20 27.00

460 7.02 2507.02 12.6 13.4 21 31.91

480 5.58 2505.58 12.8 13.4 20 25.36

500 5.4 2505.4 12.8 13.4 20 24.55

520 4.86 2504.86 12.6 13.4 20 22.09

Average 7.12 2507.12 12.64 13.24 19.59 32.36

Note: Outlet pressure: 1.52 bar (constant)

Figure C.3 Flux and feed pressure of MF process

1

1.5

2

2.5

3

3.5

20

25

30

35

40

45

50

0 60 120 180 240 300 360 420 480


Fee

d P

ress

ure

(b

ar)

Flu

x (

LM

H)

Flux Feed Pressure

After air backwash

103

Referring to Figure C.3, air backwashing during the experiment were able to recovery flux

and go up around 5 to 10 LMH.

2. Operation data of NF

Only 55.6% of water recovery was calculated in NF process since 63 liter of feed water (MF

permeate) was fed to feed tank of NF pilot unit, but only 35 liters of permeate was collected

and 28 liters was NF retentate. Table C.2 and Figure C.4 show all operation data from NF

process.

Figure C.4 Flux and brix concentration at feed

Table C.2 Operation Data of NF Process

Time Flow (L/h) Pressure (bar) Temp.

(oC)

Brix Conc. (%) Flux

(LMH) Permeate Retentate Inlet Outlet Permeate Feed

0 23 680 15 13 18 5.4 11.6 3.30

5 18 680 15.3 13.5 18 5.4 11.6 2.58

10 18 690 15.4 13.5 18 5.4 12.2 2.58

15 18 700 15.6 13.5 19 5.8 12.2 2.58

20 17 700 15.7 13.5 19 6 13 2.44

25 17 700 15.7 14 20 6 13 2.44

30 16 700 15.8 14 21 6.2 13.2 2.30

35 16 700 15.8 14 21 6.4 13.2 2.30

40 15 700 15.8 14 22 6.6 13.8 2.15

45 15 700 15.8 14 21 6.8 13.8 2.15

50 12.5 725 15.8 14 19 7 14.2 1.79

55 12 725 16 14 18 7 14.2 1.72

60 12 725 16 14 17 7 14.6 1.72

65 11 725 16.1 14 16 7.4 14.6 1.58

70 10 750 16.5 14 15 7.4 14.6 1.43

75 10 750 16.4 14 15 7.6 14.6 1.43

80 10 750 16.4 14 15 7.6 15.2 1.43

85 10 750 16.5 14 15 8 15.2 1.43

90 10 750 16.5 14 16 8 15.6 1.43

10

11

12

13

14

15

16

17

18

1

1.5

2

2.5

3

3.5

0 20 40 60 80 100 120

Fee

d B

rix (

%)

Fee

d P

ress

ure

(b

ar)

Flu

c (L

MH

)

Time (min)

Flux Brix Feed Pressure

104

Time Flow (L/h) Pressure (bar) Temp.

(oC)

Brix conc. (%) Flux

(LMH) Permeate Retentate Inlet Outlet Permeate Feed

95 10 750 16.4 14 16 8.2 15.6 1.43

100 10 750 16.4 14 17 8.2 16.2 1.43

105 10 750 16.4 14 18 8.8 16.2 1.43

110 10 750 16.4 14 18 9 16.2 1.43

115 10 750 16.4 14 19 9.2 16.2 1.43

120 10 750 16.4 14 19 9.4 16.8 1.43

125 10 750 16.3 14 20 9.8 16.8 1.43

130 10 750 16.1 14 21 10 17.4 1.43

Average 12.98 725.93 16.03 13.89 18.19 7.39 14.51 1.86

3. Chemical analysis

All of water samples, taken during MF and NF pilot test, were analyzed in LPE’s laboratory

and shown in the following table.

Table C.3 Orange Juice Quality of MF and NF Process

Parameter Unit

MF Process NF Process

MF feed

(Orange

juice)

MF

permeate

MF

retentate

NF feed

(MF

permeate)

NF

permeate

NF

retentate

Appearance - Orange

and turbid

Yellow

and clear

Orange

and turbid

Yellow and

clear

Yellow

and clear

Yellow

and clear

Turbidity NTU >1,100 0.1 >1,100 0.1 <0.1 0.2

pH - 4 4 4 4 3.9 3.8

Conductivity µS/cm 3,990 3,880 4,030 3,880 3,600 4.370

Brix % 13 12.4 13.4 12.4 8 14.7

Figure C.5 Appearance of MF and NF feed/permeate/retentate

105

IV. Discussion and Conclusion

Microfiltration process has a significant ability in removing suspended solids and most of

colloidal solids from original orange juice which is suitable and meet the criteria as feed of

nanofiltration. However brix, conductivity and pH of permeate and retentate of MF have no

significant difference from the original orange juice. The tendency of filtration flux of MF

Test was gradually decreased during filtration, but it was enhanced with air backwashing for

short duration.

For NF process, some portion of sugar content can pass through the NF membrane to

permeate due to very low sugar rejection of NF, 35.48%. Besides, the brix value of NF

retentate is still high which shows that NF retentate containing with high sugar content.

For further study on MF retentate, NF permeate and retentate are needed to determine the

possibility of sugar reduction in orange juice with 1000 Daltons of MWCO NF membrane.

In case of the unsatisfied result, changing the suitable or smaller MWCO of NF membrane

should be considered and run pilot experiment to get more exact result again.

V. Lesson Learned

The vital lesson from this case study was how real application of sugar removal of one

industry was taken place. Normally, in daily life, people always utilizes one product without

knowing how industry did. As a student, we learned a lot things at school, but in real situation

it might be something different from theory or it could show as how theory is applicable to

real situation.

As can see here, application of MF and NF membrane were applied to remove suspended

and sugar in orange juice which normally people consumes it without understand how it was

done. Theory only can provide us some references of application, and say that this membrane

can remove this and cannot removal this. However, in real application, sometimes it might

not working at all.

In this case study, Diafiltration was applied as well which is a technique that uses UF or NF

membranes to completely remove, replace, or lower the concentration of salts or solvents

from solutions containing proteins, peptides, nucleic acids, and other biomolecules by

adding water (Pall, 2013). Continuously water were added, at the same amount of permeate

taken out, to avoid the increasing of viscosity which could lead to membrane fouling.

106

Case #2: Hardness and Silica Removal by Chemical Precipitation and Duraflow


Feed water source : Well water from Sanguan Wongs Industries Co.,Ltd

Testing date : October 02, 2013

Objective : Hardness and silica reduction

Membrane type : Duraflow DF 401

Membrane area : 0.28 m2

Membrane configuration : Inside-out


II. Test Procedure

- Bench Test:

- Pilot test:

-

Pilot test was run by recirculation both concentrate and filtrate back to feed tank for 4 hours,

then filtrate was collected in separated tank (Figure C.6).

Figure C.6 Duraflow pilot unit with feed and filtrate appearance

Well water pH 9.5 (30min) pH 11.3 (40min)

MgCl2=3.8g/L

Na2CO3=0.5g/L

NaOH 50% NaOH 50%

Well water

(110L)

pH 9.5

(30min)

pH 11.3

(40min)

MgCl2=3.8g/L

Na2CO3=0.5g/L

48mL NaOH 50% 370mL NaOH 50%

DF 401

Feed Filtrate

107

Figure C.7 Experimental set-up of Duraflow

III. Result and Discussion

Table C.4 Result of Operation Data at 2 bar

Time

(min)

Flow Flux

(LMH)

Permeate water

Permeate Concentrate pH Turbid

(NTU)

Total Hardness

(mg/L as CaCO3)

Silica

(mg/L)

0 400 8400 1429 11.4 3 10.1 7.9

15 260 8540 929 - - - -

30 210 8590 750 11.5 0.3 10.1 7.78

45 180 8620 643 - - - -

60 160 8640 571 11.5 0.3 10.1 7.37

75 150 8650 536 - - - -

90 130 8670 464 11.48 0.5 10.1 7.26

105 120 8680 429 - - - -

120 110 8690 393 11.46 0.4 8.08 6.86

135 110 8690 393 - - - -

150 110 8690 393 11.44 0.5 8.08 6.61

165 110 8690 393 - - - -

180 110 8690 393 11.42 0.5 8.08 6.42

195 110 8690 393 - - - -

210 110 8690 393 11.4 0.4 8.08 6.14

225 110 8690 393 - - - -

240 110 8690 393 11.42 0.5 8.08 5.91

255 110 8690 393 11.42 0.4 8.08 5.6

Average 537.83 11.45 0.42 8.75 6.66

Note: Inlet pressure: 2 bar (fixed)

Outlet pressure: 0.3 bar (constant)

Different pressure: 1.7 bar (constant)

108

Due to high pH of filtrate water from Duraflow, it was neutralized with hydrochloric acid to

bring pH down to around 7, and the result of before and after neutralization is shown in Table

C.5.

Table C.5 Chemical Analysis

Parameter Unit

Bench Test Pilot Test

Well

water

After

treatment

Well

water

After

treatment

After

Neutralization

Turbidity NTU - - 16.5 0.5 0.5

pH - - - 7.12 11.42 7.22

Conductivity µS/cm 2,040 7,110 2,490 10,270 8,820

P-Alkalinity mg/L as CaCO3 0 500 0 1,200 -

M-Alkalinity mg/L as CaCO3 400 280 500 560 -

Total hardness mg/L as CaCO3 750 17.5 690 8.08 -

Calcium hardness mg/L as CaCO3 515 0 412 0 -

silica mg/L as SiO2 113 6.33 78.52 5.76 -

According to result of operation, the graph of flux with different pressure was plotted and

shown in Figure C.8.

Figure C.8 Flux and pressure vs. Time

IV. Lesson Learned

From this case study, the lesson learned which we could figure out was how chemical

treatment could enhance the performance of MF in moving suspended solids and some other

constituents. Large amount of hardness and silica were decreased in this case study where

MF only could achieve such a result. Moreover, it shows as well how people underground

water (well water) was treated to utilize in industry by using only chemical treatment process

with MF membrane.

0

0.5

1

1.5

2

2.5

0 50 100 150 200 250

300

500

700

900

1100

1300

1500

Time (min)

Pre

ssu

re (

bar)

Flu

x (

LM

H)

Flux (LMH)

109

Case #3: Turbidity Removal with Ceramic Membrane Pilot Unit


Feed water source : Chao Praya River


Objective : Investigate the declination of flux and water recovery

Membrane type : Ceramic Membrane (CMF2-M)

Membrane area : 0.22 m2

Membrane configuration : Inside-out


Feed characteristic : High turbidity (88.9 NTU)

II. Test Procedure

Figure C.9 Ceramic membrane pilot test unit

The test was conducted into two stages:

1. Re-circulate running with feed water: The feed water was pumped from feed tank by

feed pump into the system, and to increase the cross flow velocity, circulation pump

was used to pump feed water to ceramic membrane house after feed pump. The

rejection and permeate of ceramic membrane were all return to feed tank. The

objective of this stage was to investigate the declination of flux. ( Experimental set-

up shown in Figure C.10)

110

Figure C.10 Re-circulation running

2. The second stage was similar to the first stage, but this time permeate was taken out

and feed water was adding continuously. All the amount of feed water and permeate

water were taken note to calculate the water recovery. ( Experimental set-up shown

in Figure C.11)

Figure C.11 Without re-circulation running


Mode Time

(min)

Temperature

(0C)

Pressure (bar) Flow (LPH) Per.

Turbidity

(NTU)

Flux

(LMH) Feed Permeate Permeate Concentrate

Re-

circ

ula

ting

0 28 2 0 125 3400 - 568.18

10 30 2 0 110 3500 0.12 500.00

20 33 2 0 108 3500 - 490.91

30 35 2 0 108 3500 0.13 490.91

40 37 2 0 108 3500 - 490.91

50 36 2 0 100 3500 - 454.55

60 35 2 0 95 3500 0.13 431.82

70 35 2 0 95 3500 - 431.82

80 35 2 0 90 3500 - 409.09

90 35 2 0 90 3500 0.1 409.09

100 34 2 0 85 3500 - 386.36

110 34 2 0 85 3500 - 386.36

111

120 34 2 0 85 3500 0.07 386.36

No

n c

ircu

late

130 33.5 2 0 80 3500 - 363.64

140 32.5 2 0 75 3500 - 340.91

150 33 2 0 75 3500 0.23 340.91

160 34 2 0 70 3500 0.42 318.18

Average 0.17 423.53

Total feed volume is 84.5 L, and total permeate volume is 65.85 L, so the concentration

volume is 18.65 L. Due to this test is batch experiment, water recovery cannot be calculated

by using flow-rate of feed and permeate, but the total volume must be used.

65.85% Recovery= 100% 77.93%

84.5

L

L

According to result above, the average of turbidity and flux were 0.17 NTU and 423.53 LMH

respectively. It showed that the removal rate of turbidity was 99.81%, and graph of permeate

flux with time could be plotted as following:

Figure C.12 Permeate flux vs Time

Flux was gradually decreased due to the increasing of feed water temperature and also the

concentration of feed water during recirculation mode.

IV. Lesson Learned

High turbidity of surface water was experimented with ceramic membrane to removal

suspended solids and turbidity. This technology is the best applicant to replace conventional

treatment plant such as coagulation and flocculation, and sedimentation tank. It could

remove substantially turbidity without using any coagulants (chemicals). That’s what we

learned from this case study.

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Flu

x (

LM

H)

Time (min)

112

Case #4: Color Removal with Nanofiltration Pilot Test


Feed water source : Ion Exchange Resin Regeneration


Objective : Color Removal

Membrane type : Nanofiltration Membrane

Membrane area : 4 m2

Membrane configuration : Spiral Wound


Feed characteristic : High Color

II. Test Procedure

Figure C.13 Experimental set-up of NF pilot test

The test was run under different feed pressure. The first phase the test was run by

recirculation all rejection and permeate in order to keep the concentration in feed tank

constant. Temperature in feed tank was controlled by using tap water. The reason of

recirculation was to determine the declination of flux by time. Every 5 minutes, Pressure

(feed and outlet), Flow of both permeate and concentrate, and temperature were recorded.

The second phase, permeate was taken out, and feed water was added to feed tank. The

amount of feed water and permeate water were measured to calculate percentage of water

recovery, and some samples also were taken to check the removal rate of the system in

different feed pressure. The different of color between feed and permeate are shown in

Figure C.15.

113

Figure C.14 NF pilot test unit

Figure C.15 Feed water and permeate water


Time Temperature

(0C)

Pressure (bar) Flow (LPH) Flux (LMH)

Feed Outlet Permeate Concentrate

0 32.5 20.4 18.5 33 675 8.25

7 33 20.3 18 34 675 8.5

10 33.5 20.2 18 35 675 8.75

11 33 25.5 24 50 600 12.5

15 34 25.5 23.5 52 590 13

20 35 25.8 24 55 600 13.75

23 35 30.2 29 74 545 18.5

25 35 30.4 29 74 545 18.5

30 35.5 30.7 29 74 500 18.5

34 36 34.8 34 90 500 22.5

40 36 35.7 32 90 500 22.5

45 36 30.6 29 71 575 17.75

114

50 35.5 30.5 29 71 575 17.75

55 35.5 30.7 29 71 575 17.75

60 36 30.8 29 71 575 17.75

65 37 31.1 29 68 575 17

70 37.5 31.3 29.5 67 575 16.75

75 38 31.6 30 64 600 16

80 40 32.2 31 58 600 14.5

85 40 32.6 32 45 600 11.25

The amount of total feed water was 60 L and permeate got from NF was 48 L. The rest 12 L

was the concentrate. The water recovery of this test is shown below:

48%Recovery= 100% 80%

60

L

L

Figure C.16 Flux and feed pressure vs. Time

The Figure C.16 illustrate the fluctuation of flux by time. The reason is that the test was run

with different feed pressure (25 bar, 30 bar, 35 bar and 30 bar), and the temperature (32-40 0C) in feed tank also up and down. That makes flux sometimes goes up and sometimes

declines. However, we can correct these fluctuation of flux by using temperature correction

factor. From Figure C.13, the color of permeate looks extremely very clear compare to the

feed water.

IV. Lesson Learned

According to theory, NF membrane could be used to removal divalent ions and color as well.

This case study, NF membrane was used to remove a very high color wastewater from ion

exchange resin generation. As the result from experiment, the permeate water was extremely

very clear, and can tell that NF membrane is really an effective technology in color removal

as in theory.

18

23

28

33

38

0

5

10

15

20

25

0 20 40 60 80

Fee

d P

ress

ure

(b

ar)

Flu

x (

LM

H)

TIme (min)

Flux Feed Pressure

115

Appendix D

Application of IMSDesign (Hydranautic Projection) Software

116

Application of IMSDesign (Hydranautic Projection) Software

I. Overview

Hydranautics Membrane Solutions Design 2012 (IMSDesign®) was utilized to simulate the

system. This simulation software is a freeware which provided by Hydranautics for

designing membrane system by using Hydranautics membrane. IMSDesign® is an accurate

prediction of performance over time and under a variety of conditions. Parameters such as

salt passage increase and flux decline due to fouling are simply reachable to the user. The

information used in the membrane selection process is provided by program, and users can

completely control it (Hydranautics, 2013). This freeware can be download at:


Before ready to use this application, some necessaries input data of this application need to

be considered and are listed as following:

- Water characteristic: pH, hardness, silica, chloride, turbidity, conductivity, etc.

- Flowrates: Feed flow, permeate flow, and concentrate flow.

- Product recovery

- Investment cost

- Electricity cost or power cost ($/kWh)

- Inhibitor cost ($/kg) and acid cost ($/kg)

- Plant life (year)

- Membrane life (year)

- Membrane cost ($/element)

Figure here below is the interface of IMSDesign® software.

Figure D.1 Interface of IMSDesign®


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II. Application

After successfully installed the software, double click on IMSDesign® shortcut on desktop

to start program. Then, click on “Design RO” to start RO system design.

a. Analysis

After clicking on “Design RO”, it will show “Analysis” window as the shown picture. This

window allow you to input all feed water characteristic and type of feed water as well.

After input some of important feed characteristic, please click on “Autobalance”, and

software will balance both positive ion and negative ion. Moreover, TDS concentration is

calculated as well (Figure D.2).

Figure D.2 Feed characteristic input

b. RO design

Once feed characteristics are completed and click on “Autobalance”, please click on “RO

Design” on Manu Bar and it will show as in Figure D.5.

Here, RO system can be designed in various condition such as multi-stages system,

concentrate recirculation, booster pump, etc. Permeate flow and product recovery are the

require data to design RO system. Here below are some applications of RO design:

- Input percentage of product recovery

and permeate flow.

- Select feed water type, or other options

like permeate blending, permeate

throttling, concentrate recirculation, and

booster pump.

- Select element type, number of elements per vessel, and number of vessel. In order

to select element type, please click on the box of “Element type”. Then, click “OK”.

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After element type and number of element and vessel were selected, average flux and

feed flow will be automatically calculated.

Figure D.3 Element selection

However, if average flux exceeded, please goes back to element type and number selection

or increase number of stage.

Figure D.4 Error due to exceeded average flux

- Then click “Run” to see the calculation sheet after data are inputted.

Figure D.5 System calculation

Error number 1 illustrates that concentration flow (2.6m3/h) is too low, while error number

2 and 3 show that concentration polarization factor (1.22) and concentrate saturation of silica

(142%) are too high.

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In order to solve these errors, percentage of product recovery should be reduced, or number

of elements and vessels should be adjusted. If it still occurs, system should include

concentration recirculation which will increase the flow of concentrate per vessel.

Figure D.6 Error due to concentration flow, polarization, and saturation factor

- Click on “Flow diagr.” to see flow diagram of the designed RO system (Figure D.10),

and click on “Print” to get report of system (Figure D.13 and D.14).

c. Calculation

- Power requirements: Click on “Calculation” on Manu Bar, then select “Power

requirement. It will show some information as shown in Figure D.7 if RO Design is

run. This section, power consumption (kWh/m3) is estimated.

- Cost: Click on “Calculation” on Manu Bar, then select “Cost”. In this part, some

requirements input are needed such as Investment cost ($), Power cost ($/kWh), Plan

life (year), Membrane life (year), Membrane cost ($/element), Inhibitor and acid cost

($/kg). As the result, Capital cost, Power cost, Chemical cost, Membrane

replacement cost, Maintenance, and Total water cost ($/m3) are calculated.

Figure D.7 Power requirements (Left) and cost (Right)

In order to get report of both Power requirement and cost, just click on “Print”.

III. Case Study

Here’s a classic case study from first stage RO of ZLD system in TPAC. Below table shows

the feed characteristic of first stage RO.

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Table D.1 Feed Characteristic

Parameter Unit Feed RO-1

Appearance - Slightly yellow

Turbidity NTU 0.18

pH - 7.6

Conductivity µS/cm 670

TDS mg/L 435.5

Total Hardness mg/L as CaCO3 151.5

Calcium Hardness mg/L as CaCO3 104

Chloride mg/L as Cl- 84.37

Silica mg/L as SiO2 43.63

a. Analysis

Figure D.8 Feed characteristic of first stage RO

b. RO Design

Figure D.9 RO design calculation of first stage RO

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Figure D.10 Flow diagram of first stage RO

c. Calculation

- Power requirement:

Figure D.11 Power requirement of first stage RO

- Cost:

Figure D.12 Cost of first stage RO

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Appendix E

Output of IMSDesign (Hydranautic Projection) Software

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Output of First Stage RO system

Figure E.1 RO design of first stage RO system-a

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Figure E.2 RO design of first stage RO system-b

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Figure E.3 Power requirement and cost estimation of first stage RO system

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Output of Second Stage RO system

Figure E.4 RO design of second stage RO system-a

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Figure E.5 RO design of second stage RO system-b

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Figure E.6 Power requirement and cost estimation of second stage RO system

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