A microbial fuel cell sensor for unambiguous measurement of organic loading and definitive identification of toxic influents

Spurr, Martin W.A., Yu, Eileen H., Scott, Keith and Head, Ian M. (2020) A microbial fuel cell sensor for unambiguous measurement of organic loading and definitive identification of toxic influents. Environmental Science: Water Research and Technology, 6 (3), 612-621. (doi:10.1039/c9ew00849g).

Abstract

Microbial fuel cells can be used as sensors to measure organic load (measured as biochemical oxygen demand; BOD) in aqueous waste streams, but electrical current output can also be affected by the presence of toxic compounds. Just as BOD is a non-specific measure of organic loading the toxic response is not differentiated for specific toxicants and thus enables a generalised toxicity level to be monitored. To date combined BOD and toxicity sensing with a MFC has not been possible without comparison with reference feeds of synthetic solutions, as a decrease in signal caused by a decrease in BOD could not be distinguished from those caused by the presence of a toxicant in the waste stream. In this work, an innovative solution using a three-stage MFC sensor configuration was developed to explicitly distinguish BOD-related and toxicity-related signal decrease. A decrease in BOD led to an initial responses in the third, followed by the second and first stage MFC. For a decrease from 360 to 60 mg L^-1 O₂ BOD₅ the decrease in normalised current density was 59%, 82% and 94% in the first, second and third MFC respectively. In studies using 4-nitrophenol as a model toxic compound, increasing 4-nitrophenol concentrations resulted in an approximately equal decrease in current in all MFC in the MFC array (63%, 66% and 74% respectively when exposed to medium containing 150 mg L^-1 4-nitrophenol). Thus the magnitude and ordering of the response allowed a decrease in signal from decreasing BOD to be distinguished from the presence of a toxic compound. Furthermore, the MFCs were capable of recovering to previous performance levels within hours of acute exposure to toxicity. The multi-stage MFC configuration therefore enabled truly combined BOD and toxicity sensing with enhanced detection capabilities without the need for a defined or synthetic reference feed.

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Contributors

Author: Eileen H. Yu

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