Study On The Denitrification Efficiency And Microbial Response Of Electrochemical Biofilter For Reclaimed Wate

Reclaimed water,as the product after treatment by municipal sewage treatment plant,contains a large amount of refractory and insoluble organic matter（R-DOM）and nitrate nitrogen（NO₃^--N）.Long-term accumulation and discharge of reclaimed water leads to pollutant concentration exceeding the threshold value accommodated by surface water,thus causing ecological risks.In view of this situation,an electrochemical biofilter was constructed in this study.The pollutant removal efficienies of the electrochemical biofilter were discussed,and the response of the electrochemical biofilter to nitrogen removal of different organic compounds was studied.Meanwhile,in order to improve the pollutant removal performance of the electrochemical biological filter,the different operating conditions of the electrochemical biological filter were optimized,and the methods and paths of pollutant removal under the experimental conditions of optimal pollutant removal performance were discussed.Finally,by mean of microbiology and metagenomic technology,the biological mechanism of endogenous denitrification driven by molecular R-DOM in electrochemical biofilter was elucidated from the perspective of microorganisms,and the R-DOM and nitrogen source homing and microbial utilization efficiency in electrochemical coupled biofilter process were explained.The following conclusions are drawn:（1）Study on the response of electrochemical biological filter to DOM in tail water.In view of the fact that it is difficult for biological filter to remove R-DOM and NO₃^--N from reclaimed water,this study constructed an electrochemical biological filter and explored the pollutant removal performance of the electrochemical biological filter.The results show that the average removal concentrations of COD,NH₄⁺-N,NO₃^--N and TN in the electrochemical biological filter are reduced by 4.43,2.1,1.65 and 0.73 mg/L,respectively.The effects of different types of organic matter on nitrogen removal in electrochemical biological filter were further studied.The results showed that the NO₃^--N removal rates of methanol and sodium acetate as carbon sources were 49.24 and 52.11%,respectively,higher than that of the electrochemical biological filter with humic acid as carbon source（46.33%）.In addition,the electrochemical biological filter has small molecular effect on humic acid in the system with humic acid as carbon source.（2）Operation efficiency optimization of electrochemical biological filter.In order to ensure that the COD and TN concentrations in the effluent of the electrochemical biofilter meet the"quasi-four"standards of surface water,the influences of three operating conditions,voltage intensity,electrode material and HRT,on the pollutant removal performance of the electrochemical biofilter were optimized.The results show that when the applied voltage intensity is 6 V,the electrode material is stainless steel mesh plate（cathode）-stainless steel mesh plate（anode）,and the HRT is 24 h,the electrochemical biofilter has the best wastewater advanced treatment efficiency.The effluent concentrations of COD,NH₄⁺-N,TN and TP after reaction are 20,0.29,1.86 and 0.16 mg/L.Effluent concentration except TN is lower than the surface water discharge standardⅣ.（3）Electrochemical contaminant removal and microbial response studies.The packing and electrode of the electrochemical biological filter were analyzed by characterization and molecular weight classification.The results showed that Fe₃（PO₄）₂·H₂O and FeOOH were present on the surface of activated carbon near the anode.The genus Hydrogenophaga,Silanimonas,Thauera,Arenimonas,and Pseudomonas with high relative abundance were enriched by the cathode.The microbial metabolic pathway analysis based on KEGGG annotation found that the microbial metabolism in the electrochemical biological filter mainly consisted of amino acid metabolism,carbohydrate metabolism and energy metabolism.