| Constructed wetland wastewater treatment technology has many advantages,such as low cost,low energy consumption,convenient management and operation,and environmental friendliness,etc.,and has been widely used in advanced treatment projects of domestic sewage tail water.The stable operation of the constructed wetland system is one of the key points for sewage purification.This study takes the Yanghu constructed wetland which has been in stable operation for 10 years as the research object.By monitoring the decontamination effect of the constructed wetland,the composition of the constructed wetland is analyzed to evaluate the operation effect of the constructed wetland and explore the decontamination mechanism of the constructed wetland.It not only provides theoretical guidance for the management and operation of constructed wetlands,but also provides new ideas for the research of constructed wetlands.The results show that:(1)Water purification effect of constructed wetland The pH and dissolved oxygen are greatly affected by temperature,and the pH value in cold season is 7.87 and 6.72 respectively.The pH value in warm season is 7.79 and 6.23 respectively.In the cold season,the maximum value of dissolved oxygen is 8.86mg/L,and the minimum value is 6.01mg/L.In the warm season,the maximum value of dissolved oxygen is 7.55mg/L,and the lowest value is 1.05mg/L.The highest and lowest conductivity in cold season is 430 μs/cm and 365 μs/cm.The highest and lowest conductivity in warm season is 369 μs/cm and 371 μs/cm.PH in the system is always in the rising stage;Dissolved oxygen decreased in constructed wetland(SD1,SD3),but increased in the effluent of SD2,plant pond and water distribution channel.The overall electrical conductivity showed an upward trend.The pH and dissolved oxygen of water in the system are correlated with the electrical conductivity.The total nitrogen concentration in the system continued to decrease,and the removal rate was greatly affected by temperature.The removal rate of 48.1%in the warm season was significantly higher than that of 10.8%in the cold season.In the warm season,the concentration of ammonia decreases step by step along with the flow direction,the lowest is 0.143mg/L,and in the cold season,the concentration of ammonia increases step by step along with the flow direction,and the highest is 3.179mg/L.Nitrite nitrogen concentration was low,and the overall trend of change showed a wave-like decline.The removal effect of nitrite nitrogen in constructed wetland was not obvious,and the highest removal rate was 0.95%.The maximum concentration of nitrate nitrogen was 4.828mg/L,and the minimum concentration was 1.120mg/L.The nitrate nitrogen removal rate in cold season was 50.9%higher than 29.5%in warm season.The total phosphorus concentration in the system reached a peak of 0.286mg/L at SD1,and then decreased gradually.The total phosphorus concentration of 0.134mg/L～0.262mg/L in cold season was higher than that of 0.142mg/L～0.230 in warm season,and the phosphorus removal rate of 40.5%in warm season was higher than that of 10.2%in cold season.The concentration of COD in the system water decreases gradually along with the flow direction.Except for SD1 and SD3,the removal rates of other constructed wetlands are all greater than zero.The COD concentration of 13.53mol/L～18.35mol/L in warm season is lower than that of 23.74mol/L～25.07mol/L in cold season,but the COD removal rate of 30%in warm season is higher than that of 10%in cold season.The concentration of chlorophyll a in the system water decreased gradually with the flow direction in warm season,and the water quality decreased from 14.962μg/L in eutrophic state to 4.549μg/L in mesotrophic state.In the cold season,the water quality increased gradually with the flow direction,from 5.390μg/L to 15.657μg/L at eutrophic state.The variation trend of chlorophyll a concentration was consistent with that of ammonia nitrogen concentration.(2)Mechanism of decontamination in constructed wetlandRegardless of the cold season and warm season,the biomass of plants in constructed wetland is Grade 1 constructed wetland>Grade 2 constructed wetland>Grade 3 constructed wetland,and the biomass of each unit in warm season is higher than that in cold season.The contents of N and P,N and P accumulation,N and P removal in warm season were 40.2058mg/g and 6.1054mg/g,2.1691g/m2 and 0.2113g/m2,and 10.494g/d and 0.547g/d,respectively,which were higher than those in cold season 3.8400mg/g and 0.4500mg/g,0.1372g/m2 and 0.0142g/m2,9.116g/d and 0.193g/d.The contents of total nitrogen and phosphorus in SD1,SD2 and SD3 were much higher than those in ZWT1,ZWT2,ZWT3 and PSQ.Acinetobacter and Bacillus were dominant in the microbial community,and the alpha diversity of SD2 samples was the highest.The benthic fauna species of the three botanical ponds were similar.The zooplankton community structure was relatively simple,and copepods were not detected.The number of zooplankton community showed the phenomenon of plant pond 1>plant pond 2>plant pond 3.Phytoplankton mainly includes cyanobacteria,diatoms,chlorophyta and euglesophyta.Diatoms had the most species,followed by chlorophyta,cyanophyta and euglesophyta. |
PDF Full Text Request