Regulation Of Hetero/Autotrophic Denitrification And Its Denitrification Performance In Electrolytic-enhanced Subsurface Constructed Wetlands

Based on the process characteristics of electrode biofilm method and artificial wetland technology,this paper introduces bioelectrochemical system into artificial wetland,constructs electrolysis-enhanced submerged artificial wetland（E-CW）,explores the optimal control of E-CW hetero/autotrophic denitrification action conditions,and improves the denitrification denitrification effect of the system on wastewater containing high concentration of nitrate nitrogen and low carbon to nitrogen ratio（C/N）.The effects of different voltage intensities,electrode placement forms,different C/N ratios and fluctuations of optical energy potential on denitrification denitrification and microbial community structure characteristics were investigated and compared with the operational performance of conventional submerged artificial wetlands.The main findings obtained were as follows.（1）When no carbon source was added to the influent water and the hydraulic retention time（HRT）and applied voltage of the system were 48 h and 1.5 V,respectively,the E-CW4effluent had the lowest total and nitrate nitrogen concentrations of（35.84±8.11）mg/L and（27.47±5.91）mg/L,respectively,and the lowest nitrite nitrogen accumulation of（1.22±0.53）mg/L.However,electrolysis measures had no significant effect on the removal of phosphorus,indicating that the appropriate voltage could enhance the denitrification denitrification performance of the wetlands.A total of 14 dominant phyla and 30 dominant bacterial orders were found in the filler samples of each wetland installation.Proteobacteria,which had the highest relative abundance（range 22.46～38.62%）and were distributed in all wetland devices,were more abundant in CWs and contained many nitrifying and denitrifying bacterial groups,which had an important role in nitrogen removal.The Firmicutes,Rhodobacterales,Chitinophagales,Burkholderiales and Saccharimonadales of Proteobacteria,and the Ignavibacteriales were more abundant in E-CWs and played an important role in denitrification process.（2）The results of the effect of carbon to nitrogen ratio on the operational effectiveness of artificial wetlands showed that the supplementation of appropriate amount of organic carbon could strengthen the denitrification performance of wetlands;compared with CWs,E-CWs had higher denitrification denitrification efficiency and produced less amount of intermediate products.The removal effect of TP decreased gradually with the increase of carbon to nitrogen ratio,but the change was not significant.Considering the wetland denitrification effect and the amount of intermediate products,the optimal operating carbon to nitrogen ratio of E-CWs was 4:1 when the system voltage was 1.5 V and HRT was 48 h.The highest TN and NO₃^--N removal rates were（62.49±8.80）%and（78.02±6.97）%for E-CW4,respectively.Electrolysis increased the p H of the water column and decreased DO and ORP,indicating that E-CW formed a relatively alkaline anoxic environment that promoted the rate of nitrogen and phosphorus removal from the artificial wetland.The electrode placement form affects E-CW nitrogen removal,and the removal rates of TN and NO3--N in E-CW with dual cathodes,（72.56±3.63）%and（69.65±4.72）%,respectively,were much higher than those with single cathodes,（57.32±6.57）%and（58.35±7.40）%,respectively,but the effect on TP removal was not significant.Therefore,the electrode placement form of double cathodes can significantly promote the denitrification efficiency of E-CW.（3）The operating test results of the PV electrolysis-enhanced artificial wetland installation throughout the year showed that the PV electrolysis-enhanced artificial wetland had better denitrification and phosphorus removal compared with the conventional artificial wetland,and the denitrification performance of E-CW2（planted plants）was significantly higher than that of E-CW1（no plants）.Nitrogen and phosphorus removal rates were lowest in both wetlands during winter,but E-CW2 still had better nitrogen removal rates.There was no significant effect of electrochemistry on TP,and the differences in phosphorus removal rates between the two wetlands were small,with seasonal trends of:spring>summer>autumn>winter.A total of 10 dominant phyla and 19 dominant orders were found in the wetland substrate microbial samples,and Proteobacteria had the highest relative abundance of（39.13±5.57）%,which is important for pollutant removal.the number and species of denitrifying bacteria were higher in E-CW2,which is consistent with the nitrogen removal results of the wetland.