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Aaron Forbis-Stokes1, Brandon Hunter1, Kathy Jooss1, Lucas Rocha Melogno1, Graham Miller1,Marc Deshusses1
1Duke University, Civil & Environmental Engineering, Duke Global Health Institute, Durham, NC; [email protected] & [email protected]
Four years of field experience piloting the Anaerobic Digestion Pasteurization Latrine
Patrick O’Meara2, Bert Knorr3, Ligy Philip4, Ramprasad Chandrasekaran4, Krithika Delhiraja4
2Wataalamu Repair & Maintenance, Eldoret, Kenya3Tesari Foundation, Toledo, Cebu, Philippines & Toronto, Canada4Indian Institute of Technology-Madras, Civil & Environmental Engineering Chennai, India
ADPLThe Anaerobic Digestion Pasteurization Latrine
ADPLThe Anaerobic Digestion Pasteurization Latrine
Open defecation… = everyday business
for about 1,100,000,000 people
2.6 billion people do not have access to
“improved” sanitation
© Bill & Melinda Gates Foundation | 4
Source: WSP analysis, using BMGF funded research
Illegally
dumped
Not effectively
treated
Effectively
treated
Drainage systems Receiving waters
9% 9% 9%1%
Leakage
Unsafely emptied
Safely emptied
Left to overflow
or abandoned
69%1%
Residential environment
79%On-site
facility
20%WC to
sewer
1%Open defecation
Untreated sludge ends in the environment (Dhaka, Bangladesh)
“INSTITUTIONAL” OPEN DEFECATION
2%
98%of fecal sludge
unsafely disposed
2%of fecal sludge
safely disposed
WSH STRATEGY
AND PRIORITIES
ADPLThe Anaerobic Digestion Pasteurization Latrine
One of the many effects of the lack of
sanitation… stunting
The Anaerobic Digestion Pasteurization Latrine6
And so Bill Gates said…
“Let’s Reinvent The Toilet”
The new toilet should:
• Remove pathogens and recover valuable resources
such as energy, clean water, and nutrients.
• Operate “off the grid” without connections to water,
sewer, or electrical lines (i.e., energy neutral).
• Cost less than 5 cents per user per day.
• Promote a decent sanitation business
The Anaerobic Digestion Pasteurization Latrine7
Sanitation Needs and Solutions
Diagram from the Bill & Melinda Gates Foundation
ADPL – this talk Supercritical
water oxidation
The Anaerobic Digestion Pasteurization Latrine8
Our Vision: Omni Processor for Fecal Waste
Sanitation for the urban
poor using supercritical
water oxidation
(SCWO)
Supercritical
treatment facility, 20
ft. container for
1000-3000 people
The Anaerobic Digestion Pasteurization Latrine
Supercritical Water Oxidation of Fecal Waste
Influent Effluent
Minerals
Typical conditions
240 bar
380-650 °C
Typical removal
COD: >99.99%
N: 98%
P: >99%
The Anaerobic Digestion Pasteurization Latrine10
Sanitation Needs and Solutions
Diagram from the Bill & Melinda Gates Foundation
ADPL – this talk
The Anaerobic Digestion Pasteurization Latrine
The ADPL: A Self-Sanitizing ToiletMinimally diluted fresh
excreta. Gravity flow
Anaerobic
digestion (AD) at
ambient
temperatures. No
mixing
Biogas from AD
powers effluent
pasteurization
system
Self-contained and simple system…
Target 10-40 users (scalable)…
Peri-urban or rural settings
Effluent reuse
fertilizer, toilet flush water
11
The Anaerobic Digestion Pasteurization Latrine
Study by Feachem et al, World Bank, 1983
Image by R. Saini, U.Toronto, 2014
12
1000 100101
Time (h)
20
70
30
40
60
50
Te
mp
era
ture
(°C
)
The effluent is NOT clean waterbut it is safe!
Effluent from our field systems
Ascaris
The Anaerobic Digestion Pasteurization Latrine
System Design Characteristics
Parameter Value
Organic Loading Rate, OLR
(kgCOD/(m3d)
1-3
Digester HRT (days) 18-60
Biogas Yield
(Lbiogas/(person day))
12-42
CH4 (% vol.) 60-65
COD Removal (%) 70-90
NH3-N out (gN/L) 3-7
Desludging frequency unknown
Heater temp (℃) 65-75
Heater HRT (hours) 1.9-4.8
13
The Anaerobic Digestion Pasteurization Latrine
System Evolution and Implementation
Philippines
2013 2014
3 systems each with
3 toilets,
~80 users total
1 system, 1 toilet,
10 users
2016: 2 more systems, 2
toilets each, ~ 20 users
Kenya India
1 system, 6 IITM campus
toilets
~40 users
201
2 L
ab
stu
die
s
14
The Anaerobic Digestion Pasteurization Latrine
System infrastructure – local materials
Concrete toilet blocks,
Philippines
Fiberglass digester, India
Plastic digesters, gas
collection drums, Philippines
Heat-exchanger, rolled
galvanize steel, Kenya
Wood and tin sheet toilet
blocks, Kenya
15
The Anaerobic Digestion Pasteurization Latrine
The Biogas-Powered Pasteurization System
Biogas-powered heater
Heat exchanger
Entire system is gravity fed
From digester
Treated effluent
The Anaerobic Digestion Pasteurization Latrine
Effluent at North Effluent at Central
Avg. St. Dev. Avg. St. Dev.
COD (mg/L) 4,540 2,550 6,450 3,530
BOD (mg/L) 2,050 1,308 3,970 1,990
TSS (mg/L) 2,130 1,620 3,570 2,200
pH 7.4 0.7 7.7 1.0
TAN (mg-N/L) 2,420 506 4,760 1,090
Performance of our two systems in KenyaAccurate sampling of the influent is impossibleCalculated inlet COD ~ 42,000 mg/L
Removal
85-89%
The Anaerobic Digestion Pasteurization Latrine
Kenya – Biogas production
0
100
200
300
400
500
600B
iogas
pro
duct
ion (
L/d
)
Date
Central Avg. Prod. North Avg. Prod. Central usage North usage
Biogas production > Biogas use
Forbis-Stokes et al. Env. Eng. Sci (2016)
N = North; C = Central
Average biogas production >290 (N) and >458 (C) L d-1
Biogas usage: 288 (N) and 432 (C) L d-1
18
The Anaerobic Digestion Pasteurization Latrine
Challenges from Long-term Operation: Kenya, July 2013 – April 2016
• Solids in effluent
• Flow blockages
• Large pulses of digested
effluent
• Operation downtime for
cleaning
• Inefficient digestion
• Low biogas yield
• Low solids removal
• Limited data collection
• Inefficient gas usage
• Highly variable waste
flow, constant gas flowSystem in Eldoret showing original digester
donated by Simgas
19
The Anaerobic Digestion Pasteurization Latrine
Improved Digesters & Data Collection• Redesigned anaerobic digester
• 4 chamber baffled reactor (2.15 m3)
• Reduced dead space
• Manufactured in Nairobi (fiberglass)
• Custom tipping bucket for flow
monitoring
• Biogas production: 329 423 L/d
Gravity feed
from 3 toilets
Heater
20
The Anaerobic Digestion Pasteurization Latrine
Better digester designComputational Fluid Dynamics (CFD) modeling:
2 m3 reactor, 120 L d-1 (50 people)
No baffles (Kenya pre April 2016) 4 baffles (new Kenya)
80% dead space 15% dead space
21
The Anaerobic Digestion Pasteurization Latrine
• Particle “Electron” microcontroller
• Temperature & flow data
• Heat control• T >72 °C = gas valve off
• T <68 °C = gas valve on, igniter sparks
• Gas on/off allows greater heating power
Low-cost Controls & Remote DAQ
Power SupplySolar Panel +
Battery
CPU
OutputsGas valve
IgniterInputs
5 Temp probes
(Primary=Heater)
Tipping bucket (flow)
Particle Electron“If Theater >72; <68…”
Cloud data
10
The Anaerobic Digestion Pasteurization Latrine
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0
10
20
30
40
50
60
70
80
1/18 1/19 1/20 1/21 1/22 1/23
Flo
w (
L/h
)
Tem
per
ature
(°C
)
Date
Heat-Exchanger Cold Inlet HX Cold Outlet Heater Flow (L/hr)
Controller Performance – Kenya, Jan. 2017
Avg. T = 69.1 ℃
91.9% >65 ℃ΔT = 17.6 ℃
23
The Anaerobic Digestion Pasteurization Latrine24
Kenya - Temperature Setpoint Change
Avg. loss at 68-72 °C: 55 W
Avg. loss at 62-66 °C: 46 W
Change T setpoint
The Anaerobic Digestion Pasteurization Latrine
3.60E+07
5.00E+05
3.65E+03
2.00E+00
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
Raw sludge Digesteroutlet
Cold outlet Heater Hot outlet
E. coli (cfu/100mL)
Pathogen indicator results – India
Non-Detect
25
ADPLThe Anaerobic Digestion Pasteurization Latrine
ADPLThe Anaerobic Digestion Pasteurization Latrine
Swine digested/treated feed
Target: 1-5 g BOD/L, 1-3 g N/L
Flow = 1.35 L/d (per filter)
Trickling filters: HRT = 6 d
NH3 NO3
• Biochar [pine]
• GAC
• Zeolite [clinoptilolite]
• Pall rings
• Gravel
Submerged filters:HRT = 3 d
NO3 N2
• Sand (S)
• Bamboo (B)
• B+S
• Eucalyptus (E)
• E+S
1
2
Trickling filters
(Nitrification)
Submerged filters
(Denitrification)
Biochar
Bamboo
15
R&D in the Lab:Post-Treatment: Biological filters for N removal
The Anaerobic Digestion Pasteurization Latrine
Performance of the filters
16
Nitrification (NH4+ to NO3
-)
NH3-N
(mg/L)
Δ(%)
Turbidity
(NTU)
Δ(%)
Influent 693 1091
Biochar 123 82 200 82
GAC 110 84 207 81
Zeolite 121 82 473 57
Pall Rings 473 32 707 35
Gravel 201 71 433 60
Denitrification (NO3- to N2 gas)
NO3-N
(mg/L)
Δ(%)
Turbidity
(NTU)
Δ(%)
Influent 305 338
Sand 221 28 56 83
Bamboo 118 61 49 86
B+S 152 50 77 77
Eucalyptus 213 30 49 86
E+S 211 31 54 84
Biochar + Bamboo filters = 55% removal of total N and 98% removal of Turbidity
The Anaerobic Digestion Pasteurization Latrine
Performance summaryKenya
(2 sites)
India Philippines
(2 sites)
# users (p) 17 35 42 11 12
Waste flow (L/d) 31.2 33.5 100 28 29
Biogas prod. (L/d) 422 423 396 215 215
Biogas use (L/d) 418 418 398 217 216
Yield (L/g COD/d) 0.32 0.30 0.14 0.19 0.19
COD removal (%) 83% 71% 92% -- --
System cost
($USD each)
$2,300 $2,600 $1,800
Life cost ($/p/d) $0.068 $0.036 $0.040 $0.072 $0.072
Assumed
42,500 g COD
/ L
28
The Anaerobic Digestion Pasteurization Latrine
Conclusions• The ADPL concept works
• Self-sustained pasteurization of digester effluent with biogas
• Simple and economical system
• Local materials, local operation
• ADPLs can run autonomously
• Maintaining temperatures between 65-75 °C
• The concept is scalable and replicable
• We are learning from 5 ADPL deployments in 3 countries
Current and future focus:
• Optimizing pasteurization design
• Effluent polishing for more reuse options
• Demonstration at greater scale
Acknowledgements
The Anaerobic Digestion Pasteurization Latrine
BACKUP SLIDES
The Anaerobic Digestion Pasteurization Latrine
Pasteurization System
Biogas-powered heater
Heat exchanger
Entire system is gravity fed
From digester
Treated effluent
31
The Anaerobic Digestion Pasteurization Latrine
System structure• Peri-urban community
• Shared plots, 15-35 residents
• Prefabricated plastic latrine slabs
• <1 L pour flush
• 2 m3 floating dome digester
• Commercially available
• 3m x 3m footprint
Squat toilet slabs
Super-structure Floating dome digester
32
The Anaerobic Digestion Pasteurization Latrine
IITM Campus, India• 2,000 L baffled digester
• 42 users per day (~100 L d-1)
• Pumping settled sewage
• Up to 627 Lbiogas d-1 (15 L p-1 d-1)
• System improvements on-going
• Controls system
January 2017 Influent Effluent
COD (mg/L) 28670 1700
BOD (mg/L) 9440 930
TSS (mg/L) 8690 400
pH 6.3 6.9
FC (MPN/100mL) 1x109 6x104Digester effluent,
not yet pasteurized
33
The Anaerobic Digestion Pasteurization Latrine
Electronics / Controls Enhancements
• Manual, on-site controls for pinch
valve--up/down manipulation and
logic-reset
• Operator control of hot surface ignitor
for manual ignition
• Thermistors encased to prevent
corrosion/failure
• Firmware and software updated
• Additional bundles/connectors added
• Field operator access to software to
adjust variables to account for
disparities between sites