Microbial fuel cell-based biosensors for estimation of biochemical oxygen demand and detection of toxicity

PhD ThesisThere is a global requirement to establish state-of-the-art monitoring techniques for analysis of water quality to ensure that standards are maintained with increasing domestic and industrial water usage. An important parameter used in water quality assessment is Biochemical Oxygen Demand (BOD), a measurement of the oxygen consumed by micro-organisms in the oxidation of biodegradable organic material. BOD measurements have been correlated with the output from Microbial Fuel Cells (MFCs), which are a potential solution for online monitoring of wastewaters. Previously studied MFC sensors have had a limited amperometric range of approximately 250 mg/l O2 BOD5; which is often attributed to substrate saturation of the anode biofilm. In this work, a proof-of-concept configuration of multi-stage MFCs connected hydraulically in series was tested extensively to eliminate the saturation effect and extend the sensing range. The summed current generated by a three-stage array was calibrated against BOD5 for different glucose-glutamic acid concentrations in artificial wastewater. A linear response was obtained up to approximately 750 mg/l O2 BOD5 with R2 > 99% and average standard deviation < 9%. The array range was three times greater than obtained with the first MFC operating individually. Batch-mode sensors were also operated to develop greater understanding of the long-term performance characteristics and establish how changes in operating parameters affect sensor calibration. Additionally, the effect of toxicant presence (4-nitrophenol) on the multi-stage sensor response was studied. Toxic and low BOD events which both resulted in current decreases could be differentiated using the MFC-based sensor. The modular mode of operation permitted highstrength BOD wastewaters to be measured online without dilution and an explicit differentiation between toxic and low BOD events based on the ordered response of MFCs. The MFC-based sensors were tested with samples of real influent wastewater and recommendations have been made for ‘best practice’ operation and calibration of MFC sensors