Study On Three-Dimensional Electrode To Enhance Electricity Generation And Nitrogen Removal Of Microbial Electrochemical System

In recent years,more and more nitrogen-contaminated water bodies have caused serious environmental pollution.Among them,ammonium,nitrite,and nitrate affect the normal life of aquatic organisms,causing serious impact on the surrounding environment,and long-term intake even endangers life.Microbial electrochemical technology has the characteristics of green,environmental protection and is widely used in water treatment.The combination of microbial electrochemical system and three-dimensional electrochemical system has a better pollutant treatment effect and improves its power generation performance,which has good development prospects.The experimental research in this paper consisted of three parts:first,three-dimensional electrode microbial fuel cell（3DMFC）was constructed to study its pollutant removal effect and power generation performance;second,the biochar three-dimensional electrode microbial fuel cells were constructed to study the effect of the different forms of biochar on the power generation and the removal of pollutant.Then its nitrogen reaction pathway was explored.Third,a microbial fuel cell-three-dimensional electrode microbial electrolysis cell system was constructed to study the effects of different operating mode,different applied voltages by MFC and different influent nitrate concentration on the removal of nitrate.The main conclusions were as follows:（1）Within a certain range,the higher COD removal efficiency,the higher voltage production and power density were obtained by the 3DMFC system.When the COD concentration was 2575 mg·L^-1,the maximum voltage could reach 275 mV,the maximum power density was 22.4 mW·m^-2.（2）Brewery wastewater with different dilution concentrations was treated by the3DMFC.The highest electricity generation was obtained when the influent COD concentration was 1968 mg·L^-1.The highest voltage,power density were 280 mV and24.2 mW·m^-22 respectively.At the same time,the highest COD removal effect of91.5%was also achieved with the influent COD concentration of 1968 mg·L^-1,and the removal efficiency of ammonium was 42.5%.（3）The biochar three-dimensional electrode microbial fuel cell had higher power generation performance and nitrogen pollution removal effect.MgO-biochar 3DMFC produced the highest power density,which was 182 mW·m^-2,and exhibited the longest voltage duration of 23 hours.The power density of the biochar 3DMFCs(96¹82 mW·m^-2)were higher than that of two-dimensional microbial fuel cell（2DMFC）(52.4 mW·m^-2)without adding biochar.（4）By means of SEM and EDS,MgO-biochar and biochar were all observed to possess rich pore structure.Some MgO nanoparticles were attached to the surface of MgO-biochar,which provided more attachment sites for microorganisms.Thereby the performance of the biochar three-dimensional electrode microbial fuel cells were better.The removal capacity of COD,ammonium and total nitrogen was:MgO-biochar 3DMFC>Biochar+zeolite 3DMFC>Biochar 3DMFC>2DMFC.Short-range nitrification and denitrification occured in MFCs.The removal of pollutants mainly depended on the action of microorganisms,and adsorption accounted for a small proportion.（5）For the removal of nitrate,the microbial fuel cells-three-dimensional electrode microbial electrolysis cell（MFCs-3DMEC）with intermittent flow operation mode had a higher removal effect of 9.8%than that of the continuous flow operation mode.When the MFCs applied the voltage of 0.9 V to 3DMEC,the MFCs-3DMEC system had the highest removal efficiency of nitrate.For nitrate concentration less than 20.6 mg·L^-11 and COD/N greater than 5:1,the remove effects of nitrate with MFCs-3DMEC and disconnected MEC were similar due to the heterotrophic denitrification.For nitrate concentration higher than 20.6 mg·L^-1and COD/N less than5:1,the supply of 0.9 V voltage from MFCs could greatly promote the removal of nitrate in 3DMEC.