integration of partial anaerobic digestion and microbial...

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


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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.


CATHODE loss of oxygen reduction capacity

The cathodes potential decreased

Anode

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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


12 3

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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


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


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

integration of partial anaerobic digestion and microbial...

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