Study On Cathode Modification And Denitrification In Bioelectrochemical System

Microbial Electrolysis Cell（MEC）can achieve autotrophic denitrification through in-situ hydrogen production,which has the advantages of environmental sustainability.Common MEC electrode materials such as graphite felt and stainless steel mesh have the advantages of low price and good chemical stability,but the surface biocompatibility and effective adsorption sites need to be further optimized to improve the MEC operating effect.Chitosan（CS）,chitosan/reduced graphene oxide（CS/rGO）material were used to modified graphite felt and stainless steel mesh electrode to explore the effect of modified electrode on MEC operation.The specific research content and results are as follows:Nitrogen-removing microorganisms with stable community structure were obtained through autotrophic domestication,composition of the community structure,nitrogen removal pathways,nitrogen removal performance and energy consumption at different current intensities were studied,and the better current intensity for subsequent experiments were selected.The results showed that the autotrophic denitrification microorganisms in this system were mainly composed of Paracoccus and Thauera;denitrification pathways included physical adsorption,electrochemical reduction,assimilation and autotrophic Denitrification,in which the autotrophic denitrification process was mainly carried out by microorganisms using hydrogen;MEC denitrification conformed to zero-order reaction kinetics,and the denitrification rate was proportional to the current intensity at low current intensity.When the current intensity was greater than 30 m A,the denitrification rate of the system decreases as the applied current intensity increases;compared the denitrification rate and operating cost,the current intensity of 4 m A was selected as the better current condition.The nitrogen removal rate was 0.95 mg·L^-1·h^-1.Graphite felt electrode and stainless steel mesh electrode were used as the matrix,CS and CS/rGO materials were used to prepare modified electrode by ice condensation induced self-assembly method.The results showed that the electrode surface showed a three-dimensional network structure after CS modification,and the electrode resistance increases;The surface of the CS/rGO modified electrode had more"folds"on the basis of the three-dimensional network structure,the electrode roughness was significantly increased,the effective site was significantly increased,and the electrode conductivity was improved.The modified electrode was applied to MEC to study the effect of electrode modification on the system nitrogen removal performance and biofilm.The results showed that the surface of the electrode modified with CS/rGO has more biomass and higher biological activity,and its nitrogen removal performance was better than that of the unmodified electrode;Under the condition of current intensity of 4 m A and influent nitrate nitrogen concentration of 35 mg/L,the denitrification rate of the reactor with the CS/rGO modified graphite felt electrode as the cathode during stable denitrification was 15.66%higher than that of the reactor with the CS modified graphite felt electrode as the cathode during the same period,33.33%higher than that of the reactor with the unmodified graphite felt electrode as the cathode during the same period.The denitrification rate of the reactor with the CS/rGO modified stainless steel mesh electrode as the cathode during stable denitrification was 19.78%higher than that of the reactor with the CS modified stainless steel mesh electrode as the cathode during the same period,87.93%higher than that of the reactor with the unmodified stainless steel mesh electrode as the cathode during the same period.In summary,the experimental results in this paper indicated that the modification of the electrode with CS/rGO was beneficial to improve the biocompatibility and effective attachment sites on the electrode surface,thereby enhanced the MEC autotrophic denitrification effect.