Microbial Fuel Cells: Carbohydrates to Electricity in a Single Step. Korneel Rabaey, Peter Aelterman, Peter Clauwaert, Willy Verstraete

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1 Microbial Fuel Cells: Carbohydrates to Electricity in a Single Step Korneel Rabaey, Peter Aelterman, Peter Clauwaert, Willy Verstraete GHENT UNIVERSITY

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3 Wastewater treatment

4 Electricity out of biomass Technology needed: Sustainable energy systems Energy efficient wastewater treatment Existing: Anaerobic digestion Generation of methane 35% recovery as electricity Not suitable for low strength influents at low temperature Microbial fuel cells provide a solution Direct substrate to electricity conversion 1 kwh electricity 0.5 m Substrate = Sugar, 3 biogas (mainly acetate, CH wastewater, everything 4 ) which is biodegradable 3 kwh heat 1 kg Sugar ~ 4.4 kwh 1 kg Sugar ~ 4.4 kwh Up to4.4 kwh electricity

5 Microbial fuel cells A microbial fuel cell is a mimic of a biological system, in which bacteria do not transfer electrons to their natural electron acceptor but use an electrode in stead. This creates the opportunity to generate electricity

6 Bacterial metabolism for fuel cells Electron Transfer donors: of electrons sugar, from acetate, a substrate wastewater, at lowfe II potential (= energy rich) to an electron acceptor at Electron high potential acceptors: O 2, NO 3-, Fe III, CO 2, H +, Electron flow from low to high potential = Electricity

7 Microbial Fuel Cell Glucose MED red e - e - MED ox H 2 O NAD + NADH CO 2 O 2 NAD + H + H + Anode Cathode

8 Electricity and efficiency P = V x I (W) E = P x t (J) C = I x t (C) 1 mol = C (F) Chemical oxygen demand (COD) 1 g COD = 1/8 mol electrons Coulombic efficiency Energetic efficiency ε coulombic I texp M = ε F n COD added energetic = V I E added t exp

9 Advantages of MFC Direct conversion of substrate to current, no losses due to incineration No gas treatments needed Reactor design can be simple No high temperature required Low sludge production in comparison to aerobic treatment Aeration can be made passive Safe feedstocks (sugar ) 17,5 Wh!

10 Bottlenecks

11 What is required when treating waste or generating energy? Operational at various temperatures Capable of biodegrading diverse and difficult substrates Capable of operating in continuous mode Long term operation required Sufficient power/current/cod conversion rate Cost - benefit

12 Research 2,5 2 I (µa) 1,5 Electrochemical analyses 1 0,5 V (mv) ,5-1 -1,5 Molecular / Microbial analyses Reactor technology

13 Tubular MFC

14 Tubular microbial fuel cells Fedwith Acetate Glucose Domestic and hospital wastewater Digester influent Different loadings Different resistances

15 Power versus time 80 Power output (W/m3) Time (d)

16 Voltage / Power Evolutions 0,6 0,5 0,4 Voltage (V) 0,3 0,2 0, Time (h)

17 Results Substrate Av. (Max.) Av. (Max.) Coulombic Av. (Max.) Energetic Losses to sulphate (kg COD m -3 ) Power (W m -3 ) Efficiency (%) Efficiency (kg COD m -3 d -1 ) 1 Acetate (0.321) Glucose (0.467) Hospital WW (0.332 ± 0.073) 52 ± 10 (90) 75 ± 7 (98) 32 ± 6 (55) ± ± 8 (66) 43 ± 9 (74) 22 ± 3 (28) ± ± 5 (48) 22 ± 5 (36) 4 ± 1² ± Av.: Average; Max.: Maximum; 1 Expressed as NAC; ² Assuming kwh kg -1 COD

18 2,5 2 1,5 1 0,5 0 Tubular MFC 3 2,5 2 1,5 1 0,5 0 0,5 1 1,5 2 2, ,5 1 1,5 2 2,5 3 COD supplied (kg COD m -3 d -1 ) COD supplied (kg COD m -3 d -1 ) COD converted to electricity (kg COD m -3 d -1 ) COD converted to electricity (kg COD m -3 d -1 ) Acetate Glucose

19 Potential losses: some insights 0,4 A B C 0,3 0,2 Voltage (V) 0,1 0-0, ,2 Time (h) 0 0,1 0,2-0,2-0,3-0,4

20 Tubular MFC Rapid and efficient conversion of acetate and glucose Limited conversion of wastewater Recalcitrant material cannot be biodegraded in the reactors Sulphate reduction creates an electron diversion Operational parameters need fine-tuning

21 Perspectives

22 The Application Niche Waste processes (material has negative value): Priority: removal of C, N and P Sub-priority: generation of current energy efficient treatment Qualitative processes (material has positive value): Priority: generation of power Sub-priority: safety and sustainability sustainable and safe electricity generation

23 Green Energy Production Potential Process design: kg COD/m 3.d Power output: 1 kw/m 3 At current cost: appr. 8000/kW installed capacity 2020 cost: est. at 4000/kW installed capacity Cost of energy generation nowadays: appr. 1000/kW installed capacity MFCs are not feasible as large scale electricity generators

24 Biodiesel Energy production Ethanol production Sugar cane Corn + Digester effluents Fossil fuel Taxes Within biorefineries crops Carbon based energy Landfill based storage Solar energy Energy to consumer via bio-process technology Medium loadings, CO 2 -emission high efficiencies + Financial stimuli + + trading CO 2 and Added Nature value Waste management Plant products Consumption Organic waste Carbon based consumables After Wens 2004

25 Energy Efficient Wastewater Treatment Average concentration WW: 0.5 kg COD/m 3 Aerobic treatment: 0.5 kwh/m 3 energy cost 1 m 3 of WW yields 0.5 kwh energy gain A P.E. delivers 200 kw useful power

26 Critical issues Nutrient removal by MFCs Nitrogen Sulphate / sulphide Phosphorus metabolism? Electrode materials Open air cathodes

27 Willy Verstraete, Marc Verhaege Thanks to Monica Höfte, Steven Siciliano, Jurg Keller, Greg Zeikus, Bruce Logan Nico Boon, Geert Lissens, Peter Aelterman, Peter Clauwaert, Liesje De Schamphelaere, Wendy Ossieur Siska Maertens, Petra Vandamme, Joris De Backere, Carmen Van Gansbeke GHENT UNIVERSITY

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