Research On Removal Of Heavy Metals By Photocatalytic Coupled Microbial Fuel Cell

Microbial Fuel Cell（MFC）can degrade organic pollutants in wastewater while directly convert chemical energy into electrical energy,which has attracted widespread attention.As an advanced oxidation technology,photocatalysis can effectively remove refractory organics in water.Heavy metal complexes are widely present in metal electroplating wastewater,which can be broken by photocatalysis,so that the heavy metal ions can be freed,and organic matter in sewage can be oxidized and decomposed.But this techology has the problems of high recombination rate of photogenerated electrons and holes,and low efficiency of degrading pollutants.The research idea of this paper is to construct a microbial fuel cell（MFC）and photoelectrocatalysis（PEC）coupling system.The output voltage of the MFC in the coupling system provides an external bias voltage to the PEC device,which reduces the the recombination rate of photogenerated electron-hole pair,so as to promote Catalytic degradation of heavy metal complexes.In this study,firstly,MFC anodes were prepared to improve the power generation of MFC by optimizing the preparation parameters of TiO₂ nanotubes,and TiO₂ nanotube electrode sheets were modified to improve their photocatalytic performance,so as to find electrodes with high photoresponsive current and good catalytic effect,which can be which can be suitable for both MFC anode and photocatalytic electrode.Then take Cu-EDTA as the target pollutant,explore the optimal operating parameters of the photoelectric catalytic oxidation process,and provide basic parameters for the subsequent coupling system operation.Finally,the MFC and PEC are coupled to explore the power generation performance and the degradation effect of the system on Cu-EDTA in different combinations of MFC and PEC coupling system.The research results are as follows:TiO₂ nanotube electrode sheets were fabricated at different anodizing temperatures to explore their electrical performance as MFC anodes.The results showed that:changing the anodizing temperature,it was found that the surface morphology changed.The TiO₂ nanotubes prepared at 45℃（named A2）had the best current output as the MFC anode.Cyclic voltammetry showed A2 has the best electrochemical activity,high electron efficiency and its resistance is the lowest;microbial community analysis shows that the abundance of electro-producing bacteria attached to A2 is relatively high,indicating that the electrode sheet prepared at this temperature as the anode of MFC has the best performance.On this basis,the TiO₂ nanotubes were modified by silver doping so as to further improve their photocatalytic performance.Scanning electron microscope（SEM）figure found that silver particles were successfully doped into TiO₂ nanotubes,silver modified doping can significantly improve the photocatalytic performance of TiO₂ nanotube photoelectrode.By comparing the TiO₂ nanotube substrate with silver-doped TiO₂nanotubes,it was found that silver doping can increase the photocurrent by 35%.The noble metal deposition prevents photogenerated electrons from migrating back to the TiO₂ surface,and photogenerated electrons and holes are effectively separated.The effects of initial concentration of Cu-EDTA solution,pH and applied voltage on the photoelectric catalytic oxidation of Cu-EDTA were studied.The results show that:in the process of photo-catalytic oxidation of Cu-EDTA,the degradation rate of Cu-EDTA showed an increasing trend with the increase of concentration,and reached the highest degradation rate at 0.025 m M;The existence form of Cu-EDTA at different pH is different.The study found that the degradation effect can be strengthened in the appropriate pH range.Under the condition of pH3,the degradation effect of Cu-EDTA is the best;When the voltage is in the range of 0-1.0 V,the degradation rate of Cu-EDTA increases with the increase of voltage,indicating that the applied bias voltage can promote the separation of photogenerated electrons and holes,which is beneficial to the degradation of Cu-EDTA;During the five-time photocatalytic oxidation process,the TiO₂ nanotube photoelectrode has good repeatability and stability,and has always maintained a good effect of degrading Cu-EDTA,with a degradation rate above 70%.By constructing a coupling system of microbial fuel cell and photocatalysis,the power generation performance of MFC in the coupling system and the degradation effect of the coupling system on Cu-EDTA under different connection methods of MFC and PEC device were studied.The results showed that when an MFC was coupled with PEC,the MFC provided an applied bias voltage of 0.528 V and a current of 0.20 m A for the PEC system.The removal rate was 51.30%,which is 1.3 times higher than it is uncoupled.The two MFCs connected in series can provide an applied bias voltage of 0.7 V for the PEC system.The circuit current is 0.38 m A.The removal rate of Cu-EDTA reached 73.57%within 4 hours,which is obviously higher than that of a single MFC system.This proves that the series system has a better effect on degradation;thereafter,two MFCs were connected in parallel to the PEC device to obtain an external bias of 0.585V,which is hardly different from the coupled system with single MFC,but the circuit current can reach 0.34m A,which is significantly higher than that of a single MFC system.The removal rate of Cu-EDTA can reach 61.54%within 4 hours,and its degradation effect is between a single MFC and two MFCs.The currents of the three coupling systems are correlated with the degradation effects.As the current density increases,the degradation rate of Cu-EDTA also increases.