| Under the dual pressures of resource-based and pollution-induced water shortages,the water situation is not optimistic in China.In addition to the presence of conventional pollutants such as nitrogen and phosphorus,special pollutants such as heavy metals,organochlorine pesticides,pharmaceuticals,and personal care products also exist in water bodies.Compared with other traditional water treatment technologies,constructed wetland is more suitable for the prevention and control of polluted micro-polluted water bodies such as rivers and lakes.Its construction is economical,maneuverable and more effective,and has a certain advantage.In this experiment,three horizontal subsurface flow constructed wetlands,such as zeolite,ceramsite and slag were established.Artificial water distribution was used to simulate the water quality of Qinghe water body that was slightly polluted.The study on the removal efficiency of conventional pollutants（COD,NH4+-N,TP）and unconventional pollutants（selected SMX as representative）in micro-polluted water by constructed wetland with different substrates.And the relationship between the temporal and spatial distribution of microbial structure and enzyme activity and the removal of pollutants in the system.This will provide basic information for the rational regulation of microbial structure in constructed wetland systems and for the study of microbiologically enhanced constructed wetlands,providing a theoretical basis for evaluating the trends and intensity of pollutant removal processes using enzyme activity.It plays a positive role in guiding the design,operation and management of the constructed wetland and filling its purification function into full play.In the study of pollutant removal efficiency in three different matrixes of constructed wetland devices,the concentration of pollutants in the constructed wetlands of different matrices basically conforms to the law that gradually decreases along the horizontal and vertical directions of the wetland bed.The removal efficiency of pollutants in the upper to the middle section is better than the middle to lower section.In the zeolite constructed wetland,the removal of COD was mainly in the first 1/2 section of the bed;the removal rate of NH4+-N was generally higher in the first 3/4 section of the bed;the removal of TP was mainly in the first 1/4section of the bed,there was also phosphorus release in the later stage;the removal of SMX was mainly concentrated in the first 1/4 section of the bed.In the slag constructed wetland,the removal of COD,NH4+-N and TP was mainly concentrated in the first 1/2 section of the bed;the removal of SMX was in the first 3/4 section of the bed,and the overall removal effect was better.In the ceramsite constructed wetland,the removal rate of COD and NH4+-N was higher in the first 1/4 section;the removal rate of TP was generally higher in the first 3/4 section of the bed;the removal rate of SMX was higher in the first 1/4 section,and the SMX concentration of the subsequent 3/4 bed remained basically unchanged.The slag constructed wetland has better effect on pollutant removal than zeolite and slag type constructed wetlands,and the effluent quality basically meets Class III standard of surface water.The slag-type artificial wetland with good pollutant removal effect was selected to carry out microbiological research and the microorganisms such as bacteria,fungi,and actinomycetes in the system were continuously monitored.The study found that the number of bacteria,the number of actinomycetes and the number of fungi decreased gradually with the decrease of seasonal temperature,and the decline trend of bacteria was the most obvious,and there was no significant difference in the number of fungi before and after the changes.Along the horizontal direction of the wetland bed,the number of bacteria gradually decreases;The number of actinomycetes gradually decreased in horizontal direction in the upper part of the bed,but did not change significantly in the middle and lower parts of the bed.Fungi did not change significantly in the horizontal direction.In the vertical direction,the number of bacteria gradually decreased,and there was a direct difference between the adjacent upper and lower layers（P<0.05）;the number of actinomycetes and fungi gradually decreased,and there was a significant difference between the upper and middle layers（P<0.01）.The difference between the middle and lower layers was not significant（P>0.05）.Through the T-test analysis of the spatial distribution pattern of each microflora in the system and the removal rate among various pollutant areas,it was found that:Bacteria,actinomycetes and the removal efficiency of COD was significantly correlated（P<0.01,r=0.96）;Bacteria and the removal efficiency of NH4+-N was correlated（P<0.05,r=0.88）;There was no correlation between bacteria,fungi,actinomycetes and the removal of TP,which reflected that the removal of phosphorus in constructed wetlands was mainly related to matrix adsorption;Actinomyces,fungi and the removal efficiency of SMX was correlated（P<0.05,r=0.94;P<0.01,r=0.96）,and the fungal association was more significant.The enzyme activities of dehydrogenase,catalase,and polyphenol oxidase were also continuously monitored.The study found that the dehydrogenase activity in the system is more sensitive to temperature as the temperature of the season decreases,and the difference between before and after decline is more obvious than catalase and polyphenol oxidase.Along the horizontal direction of the bed,the activity of dehydrogenase gradually increases and then decreases.The activity of catalase and polyphenol oxidase is gradually reduced.Along the vertical direction of the bed,the activity of dehydrogenase is gradually reduced;The activity of catalase gradually decreased from the upper layer to the middle layer,and the activity of catalase in the middle and lower layers had no significant difference.Through the T-test analysis of the spatial variation of the activity of each enzyme in the system and the removal rate of each pollutant area,it was found that:Dehydrogenase activity and catalase activity were correlated with COD removal（P<0.05,r=0.88;P<0.01,r=0.98）,and the activity of catalase was more correlated with the removal of the enzyme,which was more reliable as the removal efficiency index of COD.The activity of dehydrogenase and the activity of polyphenol oxidase were correlated with the removal of SMX（P<0.05,r=0.95;P<0.05,r=0.88）.Dehydrogenase activity was more reliable as the removal efficiency index of SMX.Through the analysis of the correlation between enzyme activity and pollutant removal,the enzyme activity can be used as an evaluation index for the removal effect of a pollutant,and it can also be targeted to change the environmental conditions of the system so that it can be efficiently removed. |
