The Effect of Oxygen Mass Transfer on Aerobic Biocathode Performance, Biofilm Growth and Distribution in Microbial Fuel Cells

E M Milner,E H Yu

doi:10.1002/fuce.201700172

Abstract

AbstractMicrobial fuel cells (MFCs) are a sustainable technology for the direct conversion of biodegradable organics in wastewater into electricity. In most MFCs, the oxygen reduction reaction (ORR) is used as the cathode reduction reaction. Aerobic biocathodes, which use bacteria as biocatalysts to catalyze the cathode ORR, provide self‐sustained, robust and highly active alternatives to chemical catalysts. However, further study of the effect of oxygen mass transfer to the biofilm and cathode materials design is needed. In the current work, two aerobic biocathodes were enriched in half‐cells, and oxygen mass transfer to the biofilm and the biofilm distribution in the porous electrode structure were investigated. It was found that mass transfer of oxygen to the aerobic biocathode was a significant factor affecting cathode ORR, evidenced by a strong correlation between the air flow rate and current. Additionally, it was found that the biofilm penetrates between 20–30% into the porous carbon electrode structure, which is likely due to oxygen mass transfer limitations. The performance of a MFC with biocatalysts at both anode and cathode (64 µW cm−2 peak power at an air flowrate of 1 L min−1) showed strong correlation with air flowrate, confirming the observation in the half‐cell system.

Highlights

Microbial Fuel Cells (MFCs) convert the chemical energy available in biodegradable organics present in wastewater into electrical energy
The findings suggest that electrons are accepted from the cathode electrode via an outer-membrane bound cytochrome, similar to Cyc2 in iron oxidizing bacteria, and are utilized in downhill and uphill electron transport pathways [31, 33]
Electrons are used to reduce oxygen to water via a terminal heme-copper oxidase on the inner membrane, producing proton motive force for ATP synthesis via ATP synthase, whilst in the downhill pathway, electrons are transferred to a NADH:quinone oxidoreductase which catalyzes the production of NAD(P)H from NAD(P)+ [31, 33]

Summary

Introduction

Microbial Fuel Cells (MFCs) convert the chemical energy available in biodegradable organics present in wastewater into electrical energy. Industrial and domestic wastewater treatment consumes 1% of the total daily electrical energy consumption in England and Wales [1], with aeration of activated sludge accounting for 56% of the energy usage in wastewater treatment [2]. This is despite the fact that wastewater contains considerable energy, with a per capita value of 1,760 kJ–1 PE–1 day–1 calculated previously for municipal wastewater [3]. Electrons, protons and oxygen combine to produce water This process generates electrical power [4,5,6,7], and is reliant upon the efficient operation of number of different components, such as the anode, cathode and membrane

Methods

Results

Conclusion