Mechanistic aspect of electrochemical signal in a microbial fuel cell-based biosensor

Lei, Hao-Yun
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University of Delaware
Due to contamination of effluent from industrial plants by toxic chemicals, the development of rapid and continuous water toxicity monitoring is an important issue. Complex influent flows into wastewater treatment plants (WWTPs) alter the routine operational condition and reduce the efficiency of the treatment process. The objective of this research is to develop a real-time device for monitoring WWTPs. A microbial fuel cell (MFC)-based biosensor is designed to detect the electrochemical signals in response of disruption by contaminants. A MFC-based biosensor can serve as a water quality emergency alarm for preventing harsh water impact. The activated sludge utilized in the experiment has DO concentration 2 ∼ 6 mg/L; MLSS ranged from 2500 ∼ 3000 mg/L; C: N: P ratio of 100: 5: 1 in nearly 99% COD removal efficiency. In the experiment, a current is generated from substrates in the synthetic wastewater instead of from the microbial metabolism. Of the metals tested Cu(II) contributes the largest current changes relative to metal ion concentration. The redox reaction of substrates is eliminated as a cause. A possible cause with divalent metals is a concentration gradient in which pH provides the most current variation. There is no significant influence of current change corresponding to pH in trivalent metals. Some secondary factors, such as ionic strength and species distribution, are also discussed. Furthermore, theoretical proton concentration variation is calculated and compared with experimental data to understand the difference between an idea model and realistic situation. The experimental data show two orders of magnitude differences from theoretical values. It is assumed that other impacts, such as sludge interaction and membrane transportation, may influence signal variation. In addition, the current variation curve equation fitted mathematically is not only an index to differentiate metal species, but also can be used to calculate concentration of metal ions. However, the accuracy of detection needs to be enhanced.