Study On Deep Phosphorus And Nitrogen Removal In Composite Constructed Wetland Of Wastewater Treatment Plant Tailwater

Responding to the problem of long process flow,large amount of denitrification carbon source and phosphorus removal agent,and complicated operation management in the process of phosphorus and nitrogen removal in the tail water of wastewater treatment plant,the deep dephosphorization and denitrification technology of constructed wetland-electrolysis-microalgae compound constructed wetland was proposed in this paper.The effects of electrode arrangement,packing type,residence time,voltage,operation mode and C/N on the dephosphorization and denitrification performance of the coupled system were investigated through the pilot test,.And the best working condition parameters were obtained.The 16S r RNA Amplicom sequencing was used to analyze the microbial population structure and functional genus in the coupled system,and the mechanism of phosphorus and nitrogen removal in the coupled system was investigated.On this basis,the research on the composite constructed wetland demonstration project was carried out.The effects of voltage and hydraulic load on the treatment efficiency of demonstration project were investigated,and the functional microbial genus and denitrification pathway in the composite system.was explored.The main conclusions were as follows:Electrode arrangement,packing type,residence time,voltage,operation mode and C/N had significant effects on phosphorus and nitrogen removal in sewage plant tail waterconstructed wetland-electrolytic coupled systems.Under the conditions of temperature 26±5℃,residence time 12h and voltage 10V,the average concentrations of NH₄⁺-N,TN and PO₄³⁺-P in the light-filled constructed wetland-three-cathode electrolytic coupling system were 0.69mg/L、5.7mg/L、0.04mg/L,respectively.The removal rates of TN and PO₄³⁺-P were 64.40%and 93.65%.The results of 16S rRNA Amplicom sequencing showed that the light-filled constructed wetland-three-cathode electrolytic coupling pilot system,the denitrifying functional genus in the lower cathode mainly included Thauera（3.02%）and Hydrogenophaga（1.66%）.The denitrifying functional genus in the anodic mainly included hydrogen autotrophic denitrifying bacteria Thauera（44.07%）and Hydrogenophaga（1.71%）.It indicated that hydrogen autotrophic denitrifying bacteria were effectively enriched in the coupled system and was an important path for deep nitrogen removal.The voltage and hydraulic load have significant effects on the phosphorus and nitrogen removal effects of the sewage plant tail water composite constructed wetland demonstration project.Under the conditions of temperature 20±4°C,voltage 15V and hydraulic load 0.012 m³/（m³·h）,after the tail water of the sewage treatment plant was treated by the composite constructed wetland,the removal rates of NH₄⁺-N,TN and PO₄³⁺-P were 65.98%,87.75%and 94.15%,respectively.And the effluent could meet the A standard discharge standard of Tianjin Municipal Wastewater Treatment Plant Water Pollutant Discharge Standard（DB12599-2015）.Among them,the removal rate of NH₄⁺-N,TN and PO₄³⁺-P for the first-grade lightweight filler constructed wetland-electrolytic and secondary lightweight filler constructed wetland-microalgae coupled system were30.60%and 35.38%,58.07%and 29.66%,80.04%and 14.11%.16S rRNA Amplicom sequencing results showed that the nitrifying bacteria in the system are mainly Devosia and Nitrospira.The denitrifying microorganisms mainly include Azospira,Bradyrhizobium,Denittrasoma,Hydrogenophaga,and Hyphomicrobium,Taueus Thauera.Among them,Hydrogenophaga and Thauera belong to hydrogen autotrophic denitrifying bacteria.