Study On Deep Purification Of Grade A Effluent From Municipal Sewage Treatment Plant By Plant Floating Bed System

China’s North China Plain area has a stable flow of urban rivers mostly for sewage treatment plant tailwater recharge,but most of the sewage treatment plants implemented in the "urban sewage treatment plant pollutant discharge standards"(GB 18918-2002)in the first class A pollutant concentration limits higher than the "surface water environmental quality standards"(GB 3838-2002)in Class Ⅳ water standards,a large number of pollutants in the sewage is discharged into natural A large number of pollutants in sewage are discharged into natural water bodies,resulting in water pollution.In order to maintain the quality of the water environment in natural water bodies and to promote the deep treatment of traditional sewage treatment plants to reduce pollution and carbon emissions,it is necessary to adopt a greener and more efficient process for the deep treatment of the primary A effluent of sewage treatment plants.The plant floating bed system,as a deformation process of the artificial wetland system,can effectively remove pollutants from the wastewater and effectively combine wastewater treatment with utilization,realizing the resource utilization of wastewater.In order to optimise the purification effect of the plant floating bed system on the primary A effluent of the wastewater treatment plant,its construction and operating conditions will be explored from the perspectives of floating bed plant species,planting density,plant ratios,hydraulic residence time and effluent location.The plant floating bed system will be constructed by selecting a single plant species,namely Acorus calamus,Zelenia,Watercress,Chrysanthemum,Reeds,Phyllostachys,Dryas,Barracuda,Water Onion,Iris,Zygomorpha and Plantain,to investigate the growth of the floating bed plants and the removal efficiency of pollutants in the simulated wastewater.The water onion,releaf,plantain and iris were found to be more effective in water purification,but the plantain was relatively poor in cold resistance,with a survival rate of 74%during the test period,and was not suitable for use as a floating bed plant for tailwater treatment in winter.The suitable planting density for plant floating beds was investigated,and water onion,rehmannia and iris were selected as floating bed plants,and plant floating beds were constructed with planting densities of 96 plants/m2,67 plants/m2 and 33 plants/m2 respectively,to investigate the growth of floating bed plants and the removal efficiency of pollutants in the simulated wastewater.The plant growth and pollutant removal efficiency of the three systems were 67 plants/m2>96 plants/m2>33 plants/m2.To explore the suitable plant ratios for the plant floating beds,Iris+Water Onion and Iris+Reptilia plant floating beds were constructed using(1:2)(1:1)(2:1)plant ratios to investigate the growth of the floating plants and the removal efficiency of pollutants in the simulated effluent.When the floating beds were constructed in a(1:2)ratio,there was a symbiotic relationship between the two plants,with the highest biological increase in the plants before and after the test,and the best pollutant removal efficiency in the simulated effluent.A dynamic test was conducted to screen the appropriate hydraulic residence time in the plant floating bed system.The Iris+water onion and Iris+releasing flower plant floating bed systems were constructed in a ratio of(1:2)with a plant density of 67 plants/m2 and fed into the primary A effluent of a wastewater treatment plant.After the basic stabilization of pollutant removal rate in the effluent,the overall performance of TN,NH4+-N,TP and COD removal rate in the water is 4d>3d>>2d for HRT,and the TN concentration is far below the requirements of GB 18918-2002 for Class A standard and close to the requirements of GB 3838-2002 for Class V water;NH4+-N and COD in the effluent from the plant floating bed all reach the requirements of GB 3838-2002 for ClassⅣ water;TP The effluent NH4+-N and COD of the plant floating bed meet the requirements of GB 3838-2002 for Class Ⅳ water;the concentration of TP meets the requirements of GB 3838-2002 for Class Ⅲ water.The plant floating bed system was investigated for the removal of pollutants along the course of the primary A effluent from the wastewater treatment plant.The change in water quality along the course of the primary A effluent from the wastewater treatment plant showed that the removal rates of TP and COD in the water increased with the growth of the test unit,while the removal rates of TN and NH4+-N in the water at the front end of the test unit were best at an HRT of 3 d.From the analysis of the test results,the Iris+Water Onion and Iris+Recluse plant floating bed systems constructed in a ratio of(1:2)with a plant density of 67 plants/m2 and a hydraulic retention time of 3-4 d were most suitable for the primary A effluent treatment of the wastewater treatment plant.