Four years of field experience piloting the Anaerobic ... Annual...Aaron Forbis-Stokes1, Brandon...

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


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


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


Sanitation Needs and Solutions

Diagram from the Bill & Melinda Gates Foundation

ADPL – this talk Supercritical

water oxidation


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%


Sanitation Needs and Solutions

Diagram from the Bill & Melinda Gates Foundation

ADPL – this talk


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


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


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


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


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 Biogas-Powered Pasteurization System

Biogas-powered heater

Heat exchanger

Entire system is gravity fed

From digester

Treated effluent


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%


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


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


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


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


• 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


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


Kenya - Temperature Setpoint Change

Avg. loss at 68-72 °C: 55 W

Avg. loss at 62-66 °C: 46 W

Change T setpoint


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



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


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


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


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


BACKUP SLIDES


Pasteurization System

Biogas-powered heater

Heat exchanger

Entire system is gravity fed

From digester

Treated effluent

31


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


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


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

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Four years of field experience piloting the Anaerobic ... Annual...Aaron Forbis-Stokes1, Brandon...

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