Integration of Partial Anaerobic Digestion and Microbial ...uest.ntua.gr/iwwatv/proceedings/presentations/22_May/SESSION_XI/6... · Integration of Partial Anaerobic Digestion and

Integration of Partial Anaerobic Digestion and Microbial Fuel Cell Technologies for

treatment of sludge from wastewater treatment plants

www.mfc4sludge.euMFC4sludge project is funded under grant: FP7‐SME‐2013/EC‐GA 605893

Conference on Industrial Waste & Wastewater Treatment & Valorization

President Hotel, Athens - 22/05/2015

E. Borràs1; D. Sánchez1, P. Bosch‐Jimenez1, S. Martinez‐Crespiera1, O. Alonso1, R. Shechter21 LEITAT Technological Centre (Barcelona, Spain),

2 Emefcy Bio‐energy Systems Ltd. 300889 Caesarea (Israel).

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Presentation Outline

1. Introduction2. Materials & Methods3. Results4. Conclusions

Athens - 22/05/2015

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Aim of the project MFC4Sludge: Reduction of sludge production in WWTPs

Objectives of the MFC4Slude approach:• Partial Anaerobic Digestion as pretreatment.• MFC optimization and scaling‐up process.• Optimized scaling‐up of the integrated 

process• Power generation improvement

• Sludge production in WWTPs varies between 10 and 30kg per capita in most European countries.

• The disposing of this sludge easily reach up to 60% of thetotal operation cost of a WWTP and consume vastquantities of energy.

1. INTRODUCTIONAthens - 22/05/2015

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Integration of partial AD+MFC

Direct energy recovery 

production as electricity

Easily degradable short organics (mainly volatile fatty acids (VFAs) and 

alcohols)

1. INTRODUCTIONAthens - 22/05/2015

Partial A

naerob

ic Digestio

nMicrobial Fue

l Cell

Adapted from Lovley, Nature 4, 2006

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Partial Anaerobic Digestion (AD)2. MATERIALS & METHODS

Athens - 22/05/2015

Microbial Fuel Cells (MFCs)• Design type: laminar (self constructed).• Air cathode• Scales tested: 150 mL, 1L and 2,5L• Electrochemical techniques: Polarization Curves (PC),

Constant Load Discharge (CLD), Constant Voltage Operation(CVO), Electrochemical Impedance Spectroscopy (EIS) andCyclic Voltamperometry (CV)

• Design type: 5liter ‐ CSTR (Major Sscience , USA).• HRT: 3‐4 days• pH: 5,2‐5,6• Temperature: 25ºC• Agitation: 200rpm• Analysis: COD, BOD, TSS, VSS, VFAs, conductivity

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Substrate Units Mean value

Sodium acetate g/l 3,20

Sodium Propionate g/l 0,38

Sodium Butyrate g/l 1,61

Acid Valeric g/l 0,26

VFA Power (mW) Energy (Wh/day) Energy (Wh/L)Acetate 12,15 0,29 0,68

Propionate 3,69 0,09 0,21butirate 3,09 0,07 0,17Valerate 3,90 0,09 0,22Mixture 7,42 0,18 0,41

• The performance of MFC fed with a VFAs‐mixture in synthetic wastewater is higher than thepropionate, butyrate and valerate separately and lower than acetate (2,5 g/L).

• It is remarkable that the output performance of VFAs mixture is 61% approximately ofacetate water and the percentage of acetate in VFAs mixture is 59 %. The main contributionin power output of VFAs mixture synthetic water is due acetate.

Feeding MFC with synthetic HA‐AD effluent3. RESULTS

Athens - 22/05/2015

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Aging MFCs: loss of power output 

• The power output of MFC decreasedfrom >10 mW to 4 mW.

• Not caused due to internal resistances.• Electrodes? verification needed!

3. RESULTSAthens - 22/05/2015

• After 6 months operation, a decrease in power output was detected.

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Aging MFCs: loss of power output   Anode/Biofilm problems?

Detail of bioelectroactive biofilm growing onanode surface

SEM images of anode surface

Detail of bioelectroactive biofilm growing onanode surface after deal&Live

3. RESULTSAthens - 22/05/2015

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Aging MFCs: loss of power output  Cathode problems?

Cathode

The cathode CV indicates less cathode performance

The current of aged MFC is higher than the initial MFC. 

3. RESULTSAthens - 22/05/2015

CATHODE loss of oxygen reduction capacity

The cathodes potential decreased

Anode

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3. RESULTSAthens - 22/05/2015

Partial Anaerobic Digestion performance

Composition of Partial AD effluent• COD depletion: <30%• pH: 5,2 ‐ 5,6• Conductivity (mS/cm): 3,1 – 6,6• N‐NH4

+ (mg/L): 180 ‐530• VFAs composition:

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Parameter Units Range (mg/L)

Acetic acid mg/l 45 ‐ 1138

Propionic acid mg/l 20 ‐ 998

Butyric acid mg/l 50 ‐ 617

Valeric acid mg/l 69 ‐ 108

Highly dependent on influent composition (solids content)

Influent of Partial AD unit:mixture of primary and secondary (1/1 V/v) WWTP sludge

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Settler Anaerobic digester Microbial Fuel Cell

Integration of partial anaerobic digestion and MFC

3. RESULTSAthens - 22/05/2015

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Intensity (mA) Power Output (mW) % P

Acetate ‐9,8 3.3 100 %

Sludge ‐4 1.4 4 %

Integration of partial anaerobic digestion and MFC at lab‐scale3. RESULTS

Athens - 22/05/2015

• Relevant decrease in Power output using sludge as substrate• The COD degradation is between 60‐85% 

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Up‐scaling MFC Units: 1‐liter device 

460 mm320 mm

• Inoculation period takes longer compared to 150mL MFCs. That was expected due to anode highersurface.

• The current density achieved is similar to thesmaller device. So, scaling‐up did not effectnegatively on current generation.

• In terms of COD removal, similar capacity wasdetermined in synthetic wastewater and sludge

3. RESULTSAthens - 22/05/2015

Inoculation period with synthetic wastewater (acetate)

Operation with sludge

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Energy balance of the HA‐AD integrated system

Energy consumption

Energy Produced

Laboratory case, which is nota real approach

3. RESULTSAthens - 22/05/2015

Path for optimizationMore research is needed

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Demonstration of Partial AD+MFC in real WWTP3. RESULTS

Athens - 22/05/2015

• P&ID scheme of the integrated solution

MFC prototypePartial AD prototype

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Demonstration of Partial AD+MFC in real WWTP3. RESULTS

Athens - 22/05/2015

• 10L prototyte (4x2,5L MFC) operating since 13/05/2015 in a real WWTP (Aduna, Spain).• Coupled to a partial AD system.• Treating a mixture of primary and secondary sludge (1:1, v/v).• 3 months operation are foreseen to validate the applicavility of the technology.

Inoculation

Integration✔

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Conclusions

• MFC technology has been validated to generate electricity from pre‐treated sludges.However, power output is significantly lower compared to synthetic wastewaters.

• MFC performance decreases after use due to cathodic catalyst loss.

• Scaling‐up of MFC successfully achieved. No loses in current density.

• Partial anaerobic digestion is capable of conditioning a mixture of primary andsecondary sludge, resulting in an effluent containing VFAs.

• Research so far has permitted the construction of a prototype that is under validationin real site.

4. CONCLUSIONSAthens - 22/05/2015

Thanks for your attention

Eduard Borràs, PhD – [email protected] Biotechnology Researcher