Performance Evaluation And Influence Factor Analysis Of Microbial Fuel Cell For BOD Determination

Biochemical oxygen demand（BOD）measurement is the main method for quantifying biodegradable organic matter（BOM）in wastewater.The relative BOM content in the wastewater determines the feasibility and difficulty of biological treatment of the wastewater.Therefore,BOD measurement is of great significance for water quality analysis and water treatment technology.Microbial fuel cell（MFC）,as an electrochemical system,can directly convert the energy released by chemical reactions into electrical energy,so they have the potential to be used as BOD sensors.At present,the electrical signals used for BOD quantifying by MFC mainly include current,voltage and coulomb quantity.In this study,the Coulombic yield（Q）was used as the electrical signal for BOD quantization,and this method was called BOD_Q.BOD_Q detection method refers to the quantitative relationship between MFC power output and anode organic substrate concentration,through the external circuit to collect the amount of charge directly calculated water sample BOM content,so the method does not need to establish a standard curve.There are three main problems in BOD_Q detection method:long response time,poor detection accuracy and narrow detection concentration range.Starting from the influence of MFC sensor structure on BOD_Q test,this paper systematically investigates the influence of several different types of MFC on BOD_Q test performance and analyzes the influencing factors,so as to select the MFC sensor suitable for BOD_Q test.Compared with the traditional five-day biochemical oxygen demand（BOD₅）detection method,the optimized MFC sensor significantly accelerated the degradation rate of organic matter and shortened the response time of BOD_Q detection method.In addition,the detection of electrical signals is more accurate than the detection of dissolved oxygen.The main contents and conclusions of this paper are as follows:（1）In view of the stability and environmental adaptability of MFC BOD_Q detection system,the mixed bacteria in the field river silt were cultivated and domesticated in this paper,and the qualified MFC inoculation fluid was screened out.According to the concentration response experiment results,the MFC BOD_Q detection system has a good response to different BOD concentration solutions,which preliminarily verifies the feasibility of BOD_Qtest method.（2）To investigate the influence of cathode electron acceptor on the performance of MFC type BOD sensor,potassium ferricyanide cathode（PF）and Air cathode（Air）MFC were started.Potassium ferrocyanide cathode significantly improved the electrical performance of MFC and reduced the internal resistance of two-compartment MFC,and the decline of internal resistance is conducive to the growth of anode microorganisms and electron transfer,and finally improved the electrical performance and coulombic efficiency of MFC.Two groups of MFCs were applied to the BOD_Q detection of simulated wastewater.The BOD_Qdetection results showed that potassium ferriccyanide,as an electronic acceptor of MFC,could effectively improve the BOD_Q response value and response signal stability for different concentrations of wastewater,especially for low concentrations of wastewater.For GGA solutions with BOD₅ concentration in the range of 25 to 400 mg L^-1,the BOD_Q assay required a response time of 10 to 48 h.（3）The influence of anode materials on the performance of MFC type BOD sensor was investigated.Two dimensional carbon cloth anode（CC）and three dimensional plane carbon felt anode（CF）were selected as anodes.Through the electrochemical test of MFC,it was found that the specific surface area of anode material was not the main reason to affect the output power of this experiment,while the pore structure of the material and the growth state of the biofilm on its surface would have an impact on the coulombic efficiency of MFC.Two groups of MFCs were applied to the detection of simulated wastewater.The BOD_Q detection results showed that the BOD_Q value of carbon felt anode MFC was more accurate and the coulomb efficiency was higher than that of carbon cloth anode MFC.For wastewater samples with BOD₅ concentration ranging from 25 mg L^-1to 400 mg L^-1,the MFC response value of carbon felt anode is higher and the response signal is more stable.This is mainly because the interchange channel structure of carbon felt anode is more conducive to the growth of microorganisms,the mass transfer of substrate and the transfer of electrons.In this paper,the influence of cathode electron acceptor and anode material on the performance of MFC type BOD sensor was investigated,and the influencing factors of BOD_Qmeasurement process were analyzed.The results show that there is no obvious difference in the surface chemical properties of the carbon fibers composed of carbon cloth and carbon felt,but the planar and three-dimensional structure of the materials will affect the performance of the BOD_Q measurement of the MFC sensor.For carbon materials（carbon cloth and carbon felt）MFC sensors,high efficiency cathode electron receptors play a leading role in BOD_Qmeasurement,especially for low concentration wastewater BOD_Q measurement is more significant.The results of this study have a certain reference significance for the practical application of MFC BOD sensor and BOD_Q detection method.