Experimental Study On Treatment Of Low C/N Ratio Tailwater By Anaerobic Tank Surface Flow Wetland

In the process of economic development in China in recent years,although the living standards of the people have been increasing,it has also brought pollution to water bodies,and the water quality has been declining,posing a serious threat to the safety of people’s lives.The tail water of sewage treatment plants that meet the discharge standards needs to be further treated to achieve the water quality goal of water function zoning.Therefore,this article studies the tail water of sewage plants with low C/N ratios,using anaerobic tanks as pre-treatment facilities and connecting surface How wetlands to form a combined artificial wetland(AT-SFSW)system.The optimal hydraulic retention time of the combined system is obtained through experiments;Analyze the actual operating effects of the combined system under different substrate types,as well as the mechanism of the impact of substrate differences on the nitrogen removal efficiency of artificial wetlands;Inspect the purification capacity of different plant types for pollutants,as well as the abundance and diversity of microbial communities.The main research results are as follows:(1)During the operation of the combined wetland system,as HRT increases,the removal rates of various pollutants show a trend of first increasing and then decreasing.When HRT is extended from 2 days to 5 days,the removal rates of CODcr,NH4+-N,NO3--N and TP increase from 79.95%,81.34%,83.38%,and 59.52%to the highest values of 83.68%,86.22%,88.99%,and 69.87%,respectively.However,when HRT is 8 days,the removal rates of CODcr,NH4+-N,NO3--N and TP decrease.When the optimal HRT is 5d,the removal rate is higliest,and the corresponding effluent concentrations of CODcr,NH4+-N,NO3-N and TP are 18.19mg/L,1.50mg/L,0.55mg/L,and 0.29mg/L,respectively.The effluent CODcr,NH4+-N,and TP can basically meet the Class Ⅳ standard for surface water.Under the optimal hydraulic retention time,the concentration of pollutants in the AC-SFCW system significantly decreased along the direction of each treatment unit.In the anaerobic tank,most of CODcr and NO3--N were removed,dropping to 18.19mg/L and 0.29mg/L,respectively;The removal process of NH4+-N and TP mainly occurs in surface flow wetlands,dropping to 1.50mg/L and 0.55mg/L,respectively.(2)The removal rates of CODcr by gravel wetlands,zeolite wetlands,and volcanic rock wetlands are 53.59%,62.23%,and 65.06%,respectively;The removal rates of NH4+-N were 57.18%,71.29%,and 58.41%,respectively;The removal rates of NO3--N were 58.40%,64.06%,and 58.41%,respectively;The removal rates of TP were 49.49%,57.27%,and 40.47%,respectively.In summary,volcanic rocks have good removal effects on the four pollutants.The Langmuir is otherm adsorption models can well fit the adsorption of nitrogen and phosphorus by three single matrices.The order of nitrogen adsorption intensity of each matrix is volcanic rock>zeolite>gravel,and the order of adsorption capacity is zeolite>volcanic rock>gravel.The order of phosphorus adsorption strength is volcanic rock>zeolite>gravel,and the order of adsorption capacity is zeolite>volcanic rock>gravel.The fitting results of the kinetic model indicate that the adsorption characteristics of the three fillers for nitrogen and phosphorus pollutants are more in line with the second-order kinetic equation,and the adsorption process is mainly chemical adsorption.(3)From the perspective of the overall removal effect of pollutants,calamus combination wetland is selected as the best treatment combination.The removal rates of CODcr,NH4+-N,NO3--N and TP in the combined wetland are 65.01%～77.45%,72.63%～80.21%,72.63%～80.21%and 68.63%～79.14%respectively.Using chaol and Simpson index to analyze the microbial community in the combined constructed wetland α Through the analysis of diversity,it can be concluded that the microbial diversity and richness of the rhizosphere soil of calamus are greater than those of cattail and reed,while the microbial diversity and richness in the anaerobic pool are less than those of the three plant types.High-throughput sequencing analysis showed that the root microorganisms and anaerobic pool microorganisms of the three wetland plants were composed of Proteobacteria and actinomycetes at the phylum level.At the subordinate level,Marseillae,Shortwave Monomonas and Nitrospillum are the main flora of the three plants;However,Marseilles,Clausellus and acidophilus are the main bacteria groups in the anaerobic pool;Marseillae,short-wave monad and nitrifying spirillum are the main nitrogen and phosphorus removal bacteria in the constructed wetland,and are also one of the reasons for the high biological nitrogen and phosphorus removal in the constructed wetland.Cluster analysis showed that the distance between the bacterial communities in the rhizosphere soil of calamus,typhus and reed was relatively close,and the community composition was relatively similar,while the distance between the sample points in the anaerobic pool and the samples of the three plant types was relatively far,and the differences between microorganisms were large.The quantitative analysis of the hydraulic retention time,substrate adsorption performance and vegetation type of the constructed wetland can provide important guidance for the in-depth understanding of the optimal hydraulic retention time,substrate performance and the optimal plant type,and also provide relevant reference for the research of nitrogen and phosphorus removal in the constructed wetland at this stage.