Purification Of Low-polluted Water And Diversity Of Microbial Communities In Constructed Wetlands

With the rapid development of China's economy,the problem of water environment pollution and ecological balance has becomed more severe.Contaminants in the river threaten the water quality and ecological safety of the river,as well as cause the river to become black-odor.Constructed wetlands?CWs?was sewage treatment processes with low cost,low construction and operation costs,convenient management,efficient and stable microbial removal efficiency,and good ecological effects,so CWs was used to purify contaminants in river water of low-concentration.Due to lack of effective governance and management,Luxi River in Chengdu was seriously polluted and could not meet water replenishment requirements of Xinglong Lake.This study relied on the ecological treatment plan of Luxi River in Chengdu to study purification effect of constructed wetlands on low-polluted water in southern part of Luxi River,in order to provide theoretical basis and technical support for the ecological treatment plan of Luxi River.In this research,CWs planted with single plant and ecological CWs planted with various plants and benthic organisms were built.The effects of CWs on the purification of low-pollution sewage and the effects of seasonal changes on treatment of water were studied,and the degradation characteristics of pollutants were described by a first-order kinetic model.In addition,based on constructing the nitrogen-phosphorus balance model of CWs,the ecological effect mechanism between substrates-plant-microbe in CWs planted single plant in summer is clarified.Through the combination of high-throughput sequencing and nitrogen-phosphorus fate analysis,the rhizosphere effects of CWs planted single plant in summer were analyzed from the quantitative point of view,and the removal proportion of microbial nitrogen and phosphorus and microbial community of structure in CWs planted single plant were discussed.The relationship between the microbial abundance of nitrogen and phosphorus removal in CWs planted single plant and the removal ratio of microbial nitrogen and phosphorus were studied.The main conclusions of the study are as follows:?1?Each group of CWs planted with single plant had a good low-polluted water purification effect.The removal rate of contaminants in CWs planted with plants were significantly improved,and the purification effect of Ceratophyllum demersum was the best,and Cyperus alternifolius was the worst.During the experiment,the average removal rates of NH₄⁺-N,TN,TP and COD in Ceratophyllum demersum?VI group?were 79.69%,74.17%,50.07%and 69.57%,and Cyperus alternifolius?V group?to NH₄⁺-N,TN,The average removal rates of TP and COD were 67.61%,67.09%,44.22%,and 53.95%.?2?Each group of ecological CWs had a good low-polluted water purification effect.The removal of nitrogen and phosphorus was the best in group E?the average removal rates of NH4+-N,TN and TP were 67.28%,64.48%and 48.23%?,and the removal of COD was the best in group G?the average removal rates of COD was 72.21%?.The removal rate of contaminants in CWs planted with plants was significantly improved.The addition of benthic organisms has no obvious effect on the removal of NH₄⁺-N,TN and TP,but has a significant effect on the removal of COD.?3?The degradation process of contaminants in CWs planted with single plant and ecological CWs were better described by the first-order kinetic model.The first-order kinetic model for the degradation of contaminants?NH₄⁺-N,TN and TP?in CWs of different groups in different seasons had a good fitting effect.In addition,the degradation rate of contaminants showed obvious seasonal differences,the degradation rate of contaminants was the highest in summer and the degradation rate of contaminants was the lowest in winter.?4?The study on the fate of contaminants in CWs planted with single plant in summer revealed that the microbial process proportion?31.34%⁴5.44%?was the main nitrogen removal pathway in CWs,and the substrate adsorption proportion?20.90%²3.91%?was the main phosphorus removal pathway in CWs.There has a competitive relationship between plant uptake and substrate adsorption of nitrogen and phosphorus accumulation.The results further revealed that planting plants in CWs not only absorbed nitrogen?5.36%⁹.79%?and phosphorus?9.68%¹6.76%?,but also enhanced purification of nitrogen?4.08%¹0.60%?and phosphorus?1.82%⁵.08%?by microbe.?5?The high-throughput sequencing analysis indicated that Pseudomonas,Acinetobacter,Bacillus,and Nitrospira were the main genus of denitrification,Pseudomonas and Acinetobacter,were the main genus of dephosphorus.In addition,Plant improved microbial abundant and biodiversity,and increased microbial abundance of denitrification and dephosphorization and the microbial removal of nitrogen and phosphorus.