Resourceful Treatment Of Domestic Sewage By The Combination Of Anoxic Sequencing Batch Reactor And Vegetable Constructed Wetlands

With the rapid development of new rural construction in China,the discharge of rural domestic sewage is increasing,and the centralized treatment of rural dispersed domestic sewage is facing great challenges.In this study,the combined process of anoxic SBR-vegetable constructed wetland was used to treat rural dispersed domestic sewage as resources.The decontamination capacity and resource recovery potential of anoxic SBR,vegetable constructed wetland and their combined process were respectively explored.The microbial community structures in anoxic SBR and constructed wetland were analyzed.The anoxic SBR was run separately under different HRT,pollution loads,and temperatures.The results show that the removal rates of NH₄⁺-N,TN,TP and COD in anoxic SBR increase with the extension of HRT,and the effect of COD removal is particularly affected by HRT.When HRT is 36 h,the removal rate is as high as 87.9%.The pollution load has a certain influence on the removal effect of pollutants in anoxic SBR,and the removal rate of pollutants decreases after the pollution load is reduced.Temperature has an obvious effect on the removal of NH₄⁺-N,TN and COD from anoxic SBR effluent.With the increase of temperature,the removal rate of NH₄⁺-N and TN increases,while temperature has little effect on the removal of TP.In order to avoid excessive consumption of carbon sources,the optimal operating condition of anoxic SBR was determined(HRT=5 h,COD 284.56 mg·L^-1,NH₄⁺-N 28.44 mg·L^-1,TP 4.85mg·L^-1).The influence of hydraulic load and pollution load on the treatment effect of constructed wetland was explored by running constructed wetland separately.The hydraulic load has a certain influence on the removal rate of NH₄⁺-N,TN and TP,and the removal rate of TP can reach more than 70%under the three working conditions,which has a great influence on the removal of COD.The smaller the hydraulic load,the better the removal effect.When the average influent COD,TP and NH₄⁺-N concentrations were 198.52 mg·L^-1,2.92 mg·L^-1and 20.69 mg·L^-1,the average effluent concentrations of constructed wetland were 64.16 mg·L^-1,0.93 mg·L^-1and 14.75 mg·L^-1,respectively.When the influent pollution load was reduced to 148.12 mg·L^-1,1.81mg·L^-1,and 15.14 mg·L^-1,the average effluent concentrations were 32.25 mg·L^-1,0.51mg·L^-1and 8.60 mg·L^-1,respectively,indicating that the effect of wetland removal was improved after the pollution load was reduced.After comprehensive consideration,the hydraulic load of constructed wetland is determined as 0.299 m³·（m²·d）^-1,the pollution load as COD 148.12 mg·L^-1,TP 1.81 mg·L^-1and NH₄⁺-N 15.14 mg·L^-1.Combining anoxic SBR and constructed wetland,the experiment was carried out under HRT 5 h,hydraulic load 0.299m³·（m²·d）^-1and natural temperature（30±2℃）with simulated domestic sewage and actual domestic sewage respectively.The results show that when the average concentrations of COD,NH₄⁺-N,TN and TP in influent water were 290.95 mg·L^-1,29.81 mg·L^-1,30.76 mg·L^-1and 4.92 mg·L^-1.After the combined process,the average effluent concentrations were 43.62 mg·L^-1,6.64 mg·L^-1,9.99mg·L^-1and 0.21 mg·L^-1.Adopting the actual domestic sewage to explore the purification efficiency of the combined process,the average concentrations of COD,NH₄⁺-N,TN and TP in the effluent were 44.54 mg·L^-1,5.19 mg·L^-1,10.00 mg·L^-1and0.23 mg·L^-1,respectively,and the removal rate can reach more than 78%.The average concentrations of COD,TN and TP in water could meet the first class A standards of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant（GB8918-2002）and NH₄⁺-N could reach the secondary standard.The soil microbial diversity of anoxic SBR sludge and constructed wetland was analyzed,it was found that the dominant groups with high relative abundance in SBR were Bacteroidota,Actinobacteriota,Pastescibacteria.Proteobacteria,Cyanobacteriota,Fimicutes,and Cyanobacteriota were dominant bacteria with high relative abundance in constructed wetlands.Water spinach grew well during the experiment.The average height of water spinach was 82 cm.The average height of each plant was 52 cm and the average weight gain of each plant was 50.8 g,which showed great economic and ecological benefits.