A Neighborhood Treatment System for

Fecal Sludge Using Supercritical Water

Oxidation

Marc A. DESHUSSES Department of Civil and Environmental Engineering

Duke University, Durham, North Carolina, USA

Project team: William Jacoby (Co-PI,

University of Missouri): Kathy Jooss,

Jose M. Abelleira-Pereira, Jose Manuel

Benjumea, Doug Hendry, Andy Miller,

Kurabachew S. Duba, Allen Busick,

Reza Espanani, Florencia Yedro, Sherif

ElsayedFunding: Bill & Melinda

Gates Foundation

© Bill & Melinda Gates Foundation | 2

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

Feces: 70-520 g/(p day) ~ 80% moisture

• Fats (5-25%)

• Carbohydrates (10-30 %)

• Nitrogenous materials (2-3%)

• Minerals (5-8%)

• Bacteria and bacterial debris (10-30%)

Where all pathogens and most of the energy is

~80 gdry , 107 g COD, ~2 g N, 1.6 MJ / (p day)

Content of Fecal Waste

Urine: 0.6 – 1.1 L/(p day)

•Organic salts (38%)

•Urea (36%)

•Organic compounds (13%)

•Ammonium salts (13%)

Contains most of the nitrogen ~7 gN/(p day)

and P ~1gP/(p d)

~440 W h/(p d)

This is a 87 kWh

dump!!!

Our Vision: Omni Processor for Fecal Waste

Sanitation for the urban poor using supercritical water

oxidation (SCWO).

Pit Latrine Collection & Transport Businesses

Supercritical treatment facility, 20 ft. container for ~1000 people

(~450-530 kWh/d)

In supercritical water, organics are rapidly

oxidized (in seconds) resulting in heat, and CO2

Benefits

o Very fast reaction (sec.)

o High conversion

to CO2 + clean water

o No SOx, NOx or odor

o No need to dry waste

o Can co-treat haz. wastes

Technical risks

o Corrosion

o Salts deposition/plugging

Pilot unit at Duke

- Heat and energy recovery

- Metallurgy and corrosion

- Process control

System Characteristics

Basic characteristics

• 100-150 kg dry/day

• 1-2 m3/day

• Assume feed ~7-15% solids

• Reactor ID: 19 mm

• Reactor length: 4.0 m

• Heat exchanger length: 39 m

• Reynolds #: 30,000 – 60,000

• Residence time in reaction

section = 2.5 to 4.5 seconds!

Anti corrosion and plugging

measures

• High Re number, slight down

slope

• Minimize transition zones

• Reactor and part of heat

exchanger in Inconel 625

• Tandem HEPS

• Periodic maintenance

Other

• Startup with isopropyl alcohol (IPA)

but any other liquid fuel will work

• Air is used as oxidant

Pilot unit construction

Process Flow Diagram

Fecal sludge

(+co-fuel)

Air

(Furnace)

ReactorGas-liquid-solid separators

CO2, N2, O2

Clean water out

Water loop

Solids

Air-water mixture

0

10

20

30

40

Heat to 400 C

supercritical

Heat of

combusion

Po

wer

(k

W)

50 kgwet/h, 10% solids basis

Air-water preheat

Fecal

Simulant

(lab only)

High solids-content (16%)

secondary sludge

Ash content: 24%

HHV: 15 MJ/kgdry

SCWO Feedstocks Processed

Isopropanol

(IPA)

Starter and

model fuel Dried chicken manure

HHV: 12 MJ/kgdry

Used as surrogates for

human fecal waste

(8-15% solids)Dog feces

HHV: 15.7 MJ/kgdry

Test run with 1.3% isopropanol

Typical IPA run: 99.9% removal

System Characterization with IPA

Effect of n: Stoichiometric factor of O2

84

86

88

90

92

94

96

98

100

102

0.0 0.5 1.0 1.5 2.0 2.5

Re

mo

val (

%)

O2 Stoichiometric factor (-)

COD Removal

IPA Removal

Secondary Sludge Treatment

Feed

EffluentEffluent

After settlingFeed

Biosolids as

received

(14 MJ/kg dry)

Slurry feed:

4.3% biosolids

9% IPA

Secondary Sludge Reactivity

Sludge behaves roughly like IPA

• IPA run - 3.2

MJ/kg

• Sludge run –

2.4 MJ/kg from

IPA + 0.8 MJ/kg

from sludge

T = 586 ± 4.9 °CT = 577 ± 12.2 °CT = 475 ± 17.5 °CT = 462 ± 7.3 °CT = 219 ± 0.8 °CT = 204 ± 8.0 °C

After reaction

Secondary Sludge Treatment Summary

Removal (%)

99.97

98.12

98.60

Influent Effluent

Analysis (9.6% IPA) Steady State

COD (mg/L) 183667 50

IPA

Removal (%)

99.97

Influent Effluent

Analysis (3% sludge + 9% IPA) Steady State

COD (mg/L) 214000 70

Total N (mg/L) 10875 200

NH3 (mg/L) 443 17.6

NO3-(mg/L) 183 15.9

NO2-(mg/L) 14.9 0.4

PO4-3

(mg/L) 4930 67.9

pH 6.8 7.02

Conductivity (?S/cm) 2560 659

Sludge +IPA

Dog Feces Treatment Slurry feed pre-processing:

14% solids (15.7 MJ/kg dry)

Effluent

Feed10% solids

+ 4% IPA

Fresh Dog Feces Treatment Summary

Removal (%)

99.97-99.85

95.32-91.70

99.91-99.56

Influent Effluent

Analysis (10% sludge + 4% IPA) Steady State

COD (mg/L) 192276 65-280

Total N (mg/L) 4704 220-420

NH3 (mg/L) 627.2 185-325

NO3-(mg/L) 98 0.3-0.8

NO2-(mg/L) 22.54 0.04-0.54

PO4-3

(mg/L) 14543.2 13.4-63.9

pH 5.95 -

Conductivity (µS/cm) 4500 -

Dog poop +IPA

Treatment of Micro PollutantsExperimental Approach

• Spiked trace contaminants during a run

• Used high concentrations of Triclosan, Acetaminophen, and

Ibuprofen

• Run with spiked IPA first, then spiked dog feces and IPA

Results

• Ibuprofen and acetaminophen (10 mg/L each) – not analyzed yet

• Triclosan:

Relevant concentration: 0.5 – 1 µg/L

Concentration spiked: 100 µg/L

Concentration in effluent (IPA treatment): ND at < 0.1 µg/L

Concentration in effluent (dog feces + IPA treatment ): < 0.1 µg/L

Removal > 99.99%

Motor

Size (kW)

Duty

Cycle

Actual

Power (kW)

Motor

Size (kW)

Duty

Cycle

Actual

Power (kW)

Furnace 15 5% 0.75 Furnace 15 90% 13.5

Air Compressor 11.2 80% 9.0 Air Compressor 11.2 80% 9.0

Water Pump 3.7 50% 1.9 Water Pump 3.7 50% 1.9

Biomass Pump 11 15% 1.7 Biomass Pump 11 15% 1.7

PC Pump 0.56 60% 0.34 PC Pump 0.56 60% 0.34

PLC and Sensors 1 100% 1 PLC and Sensors 1 100% 1

Steam Generation -4 100% -4 Net Electric Power Draw (kW): 27.3

Gaseous Expansion -0.1 100% -0.1 Gasoline Equilivance* (gal/day): 49

Net Electric Power Draw (kW): 10.4

Gasoline Equilivance* (gal/day): 18

Current and Projected Energy Balance

Currently:

17 kW heat

loss in final

effluent

cooling and

~10 kW heat

losses

Optimized design:

• Turn of furnace (autothermal)

• Recover energy from gas expansion (3-6 kW)

Expected draw ~10 kW

Concluding Remarks: Why I am Optimistic…

• SCWO achieves both waste treatment and pathogen

control extremely fast. We can even co-treat

hazardous wastes and produce clean water, without

odor, SOx, or NOx emissions…

• Selling “high value added” by products can be a driver

Sell a 10 L shower 5-10 cents

= $1.7-3.4 per kWh!

• But many challenges remain…

Acknowledgments

Gates Foundation for funding

marc.deshusses@duke.edu http://sanitation.pratt.duke.edu/

Some Lessons LearnedDesign

• Pumping slurries at low flow and high pressure is a challenge

• Compression fittings in temperature zones

above 350 °C = high failure rate

Operation

• Capillary depressurization system is difficult to control during

start up and shut down

• Hair, grit and other “stuff” causes problems during preprocessing

• Foam in the HEPS can affect level sensor reading

Modeling

• Losses play a crucial role, requires some tricks in Aspen

Future directions

• Modify prototype for improved thermal efficiency

• Replace slurry pump

• Experimental validation campaign – Model validation

• Design and build second prototype

• Technology demonstration in less developed country