Microbial Fuel Cell Sensor To Monitor Nitrate In Aquatic Environment

Confronted with the increasingly serious nitrate contamination,it's urgent to timely monitor the nitrate concentration,in order to take effective measures in time and further ensure the ecological security and human health.Microbial fuel cell?MFC?based biosensor,usually set bioanode as sensing element,employs exoelectrogen as the indicator organisms for organic matter and heavy metal ion detection,where the organic matter acts as electron donor and toxins like heavy metal ion directly inhibits the activity of the exoelectrogen.The nitrate can be detected by MFC sensor as well,as it can act as electron acceptor and compete for the electrons produced by organic matter?OM?oxidation on the anode.However,the voltage drop was too small?with a voltage drop ratio of⁵%?to create a biosensor warning.The reason lies in that:the previous studies of MFC sensors all employed a closed external circuit for BOD,toxins and nitrate detection;But for nitrate monitoring,the reaction rate would decrease with higher electrode potential applied,implying that the nitrate had limited ability to compete with the anode for the electrons.This study employed an open external circuit to operate an microbial fuel cell?O-MFC?sensor for real-time nitrate monitoring,and achieved surprisingly greater sensitivity?4.42±0.3 to 6.66±0.4 mV/?mg/L??when the nitrate was at a concentration of10⁴0 mg/L,5⁷ times higher than that of the MFC sensor with a closed circuit?C-MFC??0.8±0.05 to 1.6±0.1 mV/?mg/L??.Besides,a dynamic model based on the circuit analysis was proposed to characterize the performance of O-MFC bioanode.It indicated that the the whole warning process was systhesised by two independent processes:electrons'consumption caused by nitrate and electrons'generation caused by organic matters.From the standpoint of the activity of electroactive microorganisms and electron donors in water,the effects of anodic potential and organic concentration on the sensitivity of O-MFC were investigated.It was found that the warning sensitivity of nitrate can be doubled in a short period of time if controlling the bioanode potential lower than open circuit potential.Moreover,it could acquire 20 times higher sensitivity after 3 weeks'running with open circuit.However,after that,the O-MFC can steady operate for 3 mouth with almost the same sensitivity.As for the organic matters,the higher organic maters concentration?5mM NaAc?will reduce 40%⁸0%warning sensitivity of O-MFC.Nevertheless,O-MFC is less sensitive to the changes of organic concentrations compared to C-MFC,especially when facing the combined shock of organics and nitrate.Before applying the O-MFC sensor to the actual acquatic environment,the effects of common interfering substances(SO₄^2-?DO?Cu²⁺)in the water body were investigated in a laboratory environment.It was found that any of them could cause obvious interference during the operating of the O-MFC.Therefore,during the nitrate warning process of actual acquatic environment?both in surface water and groundwater?,O-MFC had abvious voltage drop?IR>75%?in short time?30 min?.