3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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POTENTIAL ENERGY RECOVERY FROM WASTEWATER TREATMENT – STUDY OF

UASB REACTOR IN ACCRA, GHANA

PRESENTED BY:

KOBINA MENSAH AFFUL

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Motivation

• GAMA - Inefficient sewage and faecal sludge

treatment facility GAMA

• Environmental Benefits• Less pollution to receiving water bodies

• Climate change – reduction in carbon emission

• Financial/Economic Benefits• Energy recovery (methane production)

• Nutrient recovery (fertilizer)

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Description of Plant

screen

Grit channel

Influent

Overflow

Grit channel

screen

Primary distribution boxes

Secondary distribution box

Tertiary distribution box

Sludge thickener

Gas hood

Pen stocks

UASB 1UASB 2UASB 3UASB 4UASB 5UASB 6

Effluent channel

CAPS

Trickling Filter

FST Trickling Filter

FST

Final Effluent to Korle Lagoon

Sea

out-

fall

Slud

ge D

ryin

g B

eds

Slud

ge D

ryin

g B

eds

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Background (AD process/ADM1 description)

AD process

Conversion processes in AD as used in ADM1

Hydrolysis

Acidogenesis

Acetogenesis

Methanogenesis

Homoacetogenic bacteria

Acetate oxidizing bacteria

Complex Organic Matter

Carbohydrates Proteins Lipids

Monosaccharides Amino Acids LCFA

Propionate, Butyrate, Valerate

Acetate

CH4, CO2

H2, CO2

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Model Development (Biochemical process Scheme)

Volatile fatty acids (SHAC)

Acidogenic bacteria (Xac)

Soluble degradable matter (Ss)

Particulate matter (Xc)

Inert soluble (Si)Inert Particulate (Xi)

Methanogenic bacteria (XCH4)

Methane gas (SCH4)

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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…Model Development (Process Matrices) …

Component

Process

Xs Xch4 Xac Xi Ss Shac Sch4 Si Rate

Hydrolysis -1 fxi_xs 1-fxi_xs-fsi_xs fsi_xs Acidification Yac -1 1-Yac

Methanogenesis Ych4 -1 1-Ych4

Decay of Xac 1-fxi_d-fsi_d -1 fxi_d fsi_d Decay of Xch4 1-fxi_d-fsi_d -1 fxi_d fsi_d Unit kg COD/m

3

Bio

deg

rad

able

susp

end

ed C

OD

Met

han

e p

rod

uci

ng

bio

mas

s

Aci

d p

rodu

cin

g

bio

mas

s

Iner

t su

spen

ded

org

anic

mat

ter

Bio

deg

rad

able

solu

ble

CO

D

Org

anic

aci

ds

Met

han

e

So

lub

le i

ner

ts

Component

Process Sch4 Rate

CH4 gas transfer -1 kLa (Sch4-64kH,Ch4ρgas,ch4)

Biochemical process matrix

Physico-chemical process matrix

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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…Model Development (Compartments & Links)

Diffusive

Advective

Bifurcation (for recirculaion)

Excess Sludge Collector

Outlet

Reactor

Headspace

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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…Model Input Parameters…

• Influent Flow

o Average daily flow measurements

• Influent COD fractionation

o Biodegradable Soluble (Ss)

o Biodegradable Particulate (Xs)

o Unbiodegradable Soluble (Si)

o Unbiodegradable Particulate (Xi)

• Kinetic Parameters

o Adopted as proposed by Bastone et al (2002)

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Model Calibration…

• Measured data (21/08/2002 – 21/11/2002):

o Average daily CH4 produced

o Average daily Effluent COD

o Average daily Effluent TSS

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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…Model Studies (Model Predictions)…

Scenario Model Prediction

CH4 (m3/d) Effluent COD Flux

(kgCOD/d)

Flux of Excess

Sludge (kgTSS/d)

1 2763 527 3574

2 2802 2354 3545

3 4266 5229 8477

4 4294 5428 8294

Model predictions for various scenarios

• Max. COD load for TF is 6,580 kgCOD/day

• Max. TSS load for sludge thickener is 7420 kgTSS/day

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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…Model Studies (Extra Organic Load)

• Qinf(septage+PT) of 780m3/d

• 80 trucks/d (average truck volume of 9.5m3)

• 30 trucks public toilet

• 50 trucks septage

• Estimated CH4 production of 4165m3/d

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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• 100kg COD is approximately 35m3 CH4. Therefore 4165m3 CH4 will represents 11,785kgCOD.

• 1tonne COD 3820kWh-e. With 0.85 efficiency of gas treatment unit and a motor efficiency of 40%, 11.785tonnes COD will generate 11.785 x 3820 x 0.85 x 40% = 15,306 kWh-e

• In Ghana, current 1kWh cost 0.17 GHC. Hence 15,306 kWh-e will cost approximately 2,602GHC

• Annually = 950,000GHC (equivalent to 475,000€)

Potential Economic Benefits

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Conclusions

• Showed applicability of simplified ADM 1 for UASB treating municipal waste water in the prediction of CH4 and effluent characteristics

• Wide uncertainty due to the unavailability of enough data for the model development, calibration and validation

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Recommendation

• Extensive study into influent characterisation of the various waste water streams

• Expansion of the model to describe other processes that were not considered under this study

• The predicted methane production could be treated with addition of extra unit and sold to the nearby brewery industry. Hence the need for an extensive financial model to determine the economic viability of this measure.

3rd Ghana Water Forum , College of Physicians and Surgeons – Accra, 5-7 September, 2011

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Thank you for your kind attention