Experimental Study On Advanced Treatment Of Wastewater Treatment Plant Effluent By Agricultural Waste Filter-Constructed Wetland Composite System

The carbon/nitrogen ratio?C/N?of domestic sewage in China is generally low,which leads to unsatisfactory biological nitrogen removal of sewage,resulting in a high concentration of nitrogen-containing pollutants in the effluent of the sewage plant?mainly nitrate nitrogen?.If the effluent is directly discharged,there is a risk of causing eutrophication of the water body.The application of constructed wetlands to the advanced treatment of effluent from sewage treatment plants has good practical prospects,but due to the lack of a carbon source in the sewage that can be used by microorganisms,it cannot effectively remove nitrogen.In response to this problem,this experiment constructed an agricultural waste filter-reed constructed wetland composite system and an agricultural waste filter-Thalia dealbata constructed wetland.The reed constructed wetland directly entering the prepared sewage was used as a control.Nitrogen?NO₃^--N?is partially denitrified in the agricultural waste filter.Organic matter in the effluent of the filter and the remaining nitrate nitrogen are further denitrified in the constructed wetland.Research indicates:?1?In the 7h static leaching experiment of 1g corn cob,corn stalk,and wheat bran,the COD release concentrations were 613.69mg/L,301.31mg/L,670.37mg/L,and the leaching TN concentrations were 9.35mg/L and 10.62mg/L,25.79 mg/L,leaching TP concentration was 3.69mg/L,1.53mg/L,9.24mg/L,and the average C/N was 65.28,29.27,26.28.In 60g corn cob,corn stalk and wheat bran upflow dynamic leaching experiments,the effluent concentrations of COD were 51.91mg/L,38.25mg/L,60.73mg/L,and the TN effluent concentrations were 1.20mg/L and 0.75,mg/L,1.38 mg/L,respectively.C/N was 40.02,39.48,34.83,and TP leaching concentrations were 0,0,and 0.08 mg/L,respectively.Comparative experimental data show that corn cob releases high concentrations of COD in static leaching,high C/N in static and dynamic leaching water,and low concentrations of TP and TN.Among the three agricultural wastes,it is most suitable as an additional carbon source for constructed wetlands.?2?It was verified by repeated leaching experiments using corn cob that 300 g corn cob was used to construct an agricultural waste filter,and the inflow water was controlled to be 1h/L.When the HRT of the water flow in the agricultural waste filter was about 40min,the COD The average concentration was 75.13mg/L,the average concentration of TN was 1.33mg/L,and the TP effluent concentration was 0.By controlling the HRT in the agricultural waste filter and controlling the inflow and outflow of water,the COD concentration of the effluent can meet the requirements of subsequent wetland treatment of NO₃^--N.?3?The experimental data show that the compound system of agricultural waste filter and constructed wetland can effectively enhance the removal effect of NO₃^--N in sewage.Under the condition that the influent NO₃^--N concentration is 15mg/L,and the wetland hydraulic retention time is 24h,as the experiment runs,the removal rate of NO₃^--N from the reed constructed wetland directly entering the prepared sewage gradually decreases from77.14%.With an average removal rate of 43.60%,the average removal rates of NO₃^--N for the compound wastewater by the agricultural waste filter-reed constructed wetland composite system and the agricultural waste filter-Thalia dealbata constructed wetland composite system were 99.18%and 98.77%,respectively.When the hydraulic retention time is 16h,the removal rate of the reed constructed wetland directly entering the prepared sewage is NO₃^--N is35.94%,the agricultural waste filter-reed constructed wetland composite system and the agricultural waste filter-Thalia dealbata constructed wetland compound The average removal rates of NO₃^--N for the prepared sewage by the system were 99.73%and 98.73%,respectively.When the hydraulic retention time is 12h,the removal rate of NO₃^--N directly into the reed constructed wetland prepared with sewage is 6.94%,the agricultural waste filter-reed constructed wetland composite system and the agricultural waste filter-Thalia dealbata constructed wetland The average removal rates of NO₃^--N for the compound wastewater by the composite system were 34.01%and 56.07%,respectively.?4?The experimental results show that the removal rate of NO₃^--N of the compound wastewater by the combined system of agricultural waste filter and constructed wetland is mainly affected by the COD concentration of the effluent of the filter,the number of microorganisms in the filter,the ambient temperature,and the hydraulic residence time of the constructed wetland.The type of planting plant has a small effect on the overall removal rate of NO₃^--N.?5?According to the analysis results of biological metagenomic classification and sequencing,it is learned that the agricultural waste filter-constructed wetland composite system can improve the microbial structure diversity in wetlands.Among the 9 samples studied,Proteobacteria,Chloroflexi,Bacteroidetes,Acidobacteria,Firmicutes,Actinobacteria is the main mycoplasma in each sample,with an average abundance of 83.65%at each stage.At the level of beta,Betaproteobacteria?Betaproteobacteria?accounted for the highest proportion in each sample,and played an important role in the denitrification of constructed wetlands.