Construction Of Cascade Constructed Wetland System And Study On Purification Efficiency Of Micro-polluted River

The eutrophication of lakes and reservoirs is an important issue facing the current water environment governance,and the influx of micro-polluted river water is one of the key factors causing eutrophication of lakes and reservoirs.This paper takes urban tail water as the main source of micro-polluted river water as the research object,constructs a cascade constructed wetland reaction system suitable for the deep purification of river micro-polluted water bodies,and studies the removal of conventional pollutants by the wetland system and the influence of parameters on the removal effect of the wetland system are studied.The structure characteristics and removal mechanism of plant,substrates and microbial communities in wetland system were analyzed.Further research and analysis of the purification effect of the micro-polluted river water purification project based on the pond-constructed wetland system provided technical support and monitoring analysis for the project.The main results obtained are:1.A set of cascade constructed wetland response system composed of plant sedimentation pond,subsurface flow wetland and ecological stability pond was established.The optimal process operating parameters of the wetland system are as follows: the operating temperature is within the range of 12～25℃,the hydraulic retention time is 36 h(based on the subsurface wetland unit).Under this parameter,when the influent water is simulated inferior to Grade V,the average removal rate of COD,ammonia nitrogen,nitrate nitrogen,TN,and TP by the wetland system is 93.95%,98.08%,90.64%,94.80%,77.91%,respectively.The conventional effluent indicators can reach the surface level III water standard,and the effluent meets the lake and reservoir water quality control standards above IV.2.The structure characteristics and removal mechanism of plant,substrate and microorganism community in wetland system are analyzed.During the operation stage of the wetland system,the assimilation,absorption and removal capacity of plants is relatively stable.Changes in plant growth conditions and chlorophyll content have little impact on the purification effect of the wetland system.The adsorption effect of the matrix on pollutants is affected by the composition and crystal structure of the matrix compound.The microbial community abundance of the subsurface wetland unit in the wetland system is higher than that of the other two pond units,and the ecological pond unit has a higher microbial diversity.Each unit contains pollutant removal functional bacteria,but the abundance is low and the difference between the units is not obvious.3.The operation effect of the Fuhe Estuary Wetland Water Quality Purification Project based on the process of "pre-precipitation ecological pond + subsurface flow wetland + aquatic plant pond" in the autumn and winter trial operation phases was systematically studied.The average removal rates of phosphorus were 18.25%,57.04%,30.16%,44.12%,and the effluent water quality except for total nitrogen,all conventional indicators reached the surface level III water standard.The wetland unit has a higher microbial abundance,and the pond unit has a higher similarity of the microbial flora.