Study On The Efficiency Of Plant Carbon Sourceenhanced Constructed Wetlands For Treating Agricultural Drainage Water In The Ulansuhai Lake

Ulansuhai lake ecosystem has been seriously damaged by the agricultural drainage water.It is urgent to strengthen the source control and the process treatment of agricultural drainage water to alleviate the eutrophication of the water body.In recent years,constructed wetland has been widely used for the treatment of agricultural drainage water.However,the removal effect has been reduced by the lack of carbon source in the system.so adding carbon source has become one of the most effective measure to improve its removal efficiency.To investigate the efficiency of adding plant carbon source to strengthen the treatment of agricultural drainage water by constructed wetland,the typical vegetation Phragmites australis and Schoenoplectus tabernaemontan were selected as the additional carbon sources.The static carbon release pattern of plant carbon souce under three pretreatment methods was analyzed.The high-quality carbon source was selected and added to the constructed wetland to clarify its promoting effect on purifying agricultural drainage water.Finally,the microbiological mechanisms of nitrogen removal process in constructed wetland were studied by fluorescence quantitative PCR and high-throughput sequencing.The main conclusions were as follows:（1）The Phragmites australis after alkali-heat treatment had the ability to continuously release carbon,which significantly improved the nitrogen and phosphorus removal effect of the constructed wetland.The average removal rates of total nitrogen and total phosphorus were up to 75.67% and 91.37%.The content of nitrogen and phosphorus released was low,resulting in less pollution to the wetland system.（2）The optimum carbon to nitrogen ratio was 5,the denitrification ratewas the strongest,so as to achieve the purpose of simultaneous enhanced nitrogen and phosphorus removal.（3）The denitrification effect of microorganisms in the bottom layer was strong with sufficient carbon source.（4）The addition of plant carbon sources had led to a higher richness and diversity of microbial communities in the constructed wetland.Proteobacteria,Actinobacteriota and Chloroflexi were the dominant bacteria at the phylum level,and "KD4-96" and Halomonas were the dominant bacteria at the genus level,which played an important role in the microbial denitrification process of the constructed wetland.（5）Aerobic microorganisms（ammonia oxidizing bacteria and nitrifying bacteria）were mostly distributed in the upper layer of the system,while anaerobic microorganisms（denitrifying bacteria）were mostly found in the lower layer of the system,showing a competitive and synergistic ecological relationship,and removed various nitrogen sources through shortcut nitrification and denitrification in the system.