Photocatalytic Microbial Fuel Cell Using Residual Sludge As Fuel To Treat Copper-containing Wastewater And Recover Coppe

Copper-containing wastewater comes from a wide range of sources.The unreasonable disposal of a large amount of copper waste liquid generated by mining,metallurgy,mechanical processing,surface treatment,and agricultural and medical industries will accumulate in organisms,endangering ecosystems and human health.Common treatment methods for copper-containing wastewater include chemical precipitation,reverse osmosis,and adsorption.However,these methods often have poor removal effect for low-concentration heavy metal wastewater.In addition,the annual output of excess sludge from urban sewage treatment plants in my country will further increase with the intensification of economic development and urbanization.Commonly used chemical,physical and other methods to treat sludge have high cost and energy consumption,and will cause problems such as secondary pollution.Microbial Fuel Cell（MFC）is a bioelectrochemical system that combines microbial technology with electrochemical technology.It uses electricity-producing microorganisms as catalysts to convert chemical energy rich in substrates into electrical energy.The excess sludge happens to be rich in available organic matter,which can be used as biomass energy for the microbial community of anode chamber to treat waste.At present,the production of electricity and the recovery of heavy metals in microbial fuel cells are still at a low level,and the properties of electrode materials,electron transfer rate and electron acceptor reduction rate and other factors limit the performance of the battery.On this basis,photocatalysis and MFC were coupled to form photocatalytic microbial fuel cell（PMFC）.Through the construction of photocatalytic MFC system,the synergy of light energy and chemical energy can be realized.Further explore the influencing factors of the system and the recovery of cathode copper,hoping to improve the power generation capacity and heavy metal recovery capacity of the battery.The main conclusions are as follows:（1）The g-C₃N₄/Mn O₂@PANI photocatalytic cathode was prepared by solution deposition and chemical oxidative polymerization,and a dual-chamber PMFC was constructed with carbon paper as the anode and excess sludge as the fuel.The specific surface area of the photocathode is 30.245 m²/g,which is 1.90 and 1.13 times that of carbon paper and g-C₃N₄/Mn O₂,respectively.The structure of the reaction interface is dense,which ensures sufficient photocatalytic reaction active sites,improves the photocatalytic activity,and enhances the power generation performance of MFC.The maximum power density of g-C₃N₄/Mn O₂@PANI photocatalytic cathode is 48.4 m W/m²,which is 4.36 and 1.39 times of that of carbon paper and g-C₃N₄/Mn O₂ photocatalytic cathode,respectively,are 11.1 m W/m² and34.8 m W/m².The internal resistance of g-C₃N₄/Mn O₂@PANI photocatalytic cathode is significantly reduced,only 475.2Ω.（2）Make full use of the ability of anode microorganisms to oxidize and decompose organic matter,use PMFC to degrade excess sludge,and realize sludge reduction and resource utilization.The COD degradation rate of g-C₃N₄/Mn O₂@PANI photocatalytic cathode PMFC was 94.8%,and that of VSS was 61.4%.The effects of changing the ratio of excess sludge to nutrient solution,the type and concentration of anode additives,different light sources,light intensity and external resistance on the PMFC anode treatment of excess sludge were explored.It was found that when 5 m L of Ca Cl₂·6H₂O with a concentration of 0.2 mol/L was added,the COD degradation rate increased to 96.4%,and the higher concentration was not conducive to the COD degradation rate;using a 250 W mercury lamp as the experimental light source could promote the degradation of organic matter;when the external resistance is 500Ω,the performance of anodized organic matter is better.（3）Utilize the reducing ability of PMFC cathode to recover Cu²⁺in Cu SO₄ solution,convert Cu²⁺into elemental Cu,and realize the transformation from solution to solid particles.The copper recovery rate of different cathodes and the change of Cu²⁺concentration during operation were explored,and the recovered copper samples were characterized.It was found that when the cathode copper concentration was 400 mg/L,the copper recovery rate of g-C₃N₄/Mn O₂@PANI photocatalytic cathode MFC was 97.6%,which is 1.43 times that of the carbon paper cathode.The recovered sample copper particles account for 76%,and the copper crystallinity is good.The controlled variable method was used to further explore the effects of different photocatalytic active substances,light source and light intensity,reactor configuration,and catholyte copper concentration on copper recovery by MFC.It was found that photogenerated holes are the key to the photocatalytic system;choosing a 250 W mercury lamp as the experimental light source can promote the recovery of Cu²⁺;when the plate spacing is120 mm,the copper recovery rate and coulomb efficiency are improved,which are 98.3%and40.2%,respectively;in the repeated experiments of the photocatalytic cathode,the copper recovery efficiency was kept above 90%;the actual copper electroplating waste liquid was used as the PMFC catholyte,and the copper recovery rate was only 90.1%.