Media Optimization And Phosphorus Removal Performance In The Surface Flow Stormwater Constructed Wetland

Urban rainfall runoff is the second largest non-agricultural point source of pollution.Nitrogen and phosphorus in rainwater runoff are one of the important causes of water eutrophication.Rainwater wetland is a typical structure of surface flow constructed wetland.It is an effective and economical technical measure to control the pollution of rainwater runoff.It purifies water mainly through the synergistic action of plant and matrix.In this study,the fillers of rainwater wetland were optimized and their removal effects on various pollutants were investigated.It provides theoretical basis and technical support for improving phosphorus removal efficiency of rainwater wetland.Ca-P and Mg-P accounted for 37.18%of the total phosphorus adsorbed by activated alumina.The zeta potential was 18.4 mV at pH=7.The high specific surface area of 174.69 m~2/g and pore volume of 0.4802 m~3/g were also beneficial to the adsorption.Fe-P and Al-P accounted for 72.47%of phosphorus adsorption on steel slag,and the adsorption was relatively stable.At pH=7,Zeta potential was-6.4 mV,specific surface area and pore volume were 0.82 m~2/g and 0.0095 m~3/g,respectively.Zeolite had a very high negative charge.At pH=7,Zeta potential was-23.1 mV,the specific surface area was very low,0.76 m~2/g,so the phosphorus fixation ability of zeolite was very weak.Three kinds of fillers,steel slag,activated alumina and zeolite,were selected through mixing proportion experiments among different fillers.When the mass ratio of No.2 steel slag,activated alumina and zeolite was 1:3:4,the phosphorus removal efficiency was the best.At this time,the phosphorus adsorption removal rate could reach90%on average,and the pH of effluent increased by only 0.98 units on average.Among the total volume of the matrix,80%was planted soil and 20%was mixed filler.The thickness of matrix was 30 cm.Two groups of wetlands with plants and without plants were set up,and 189 reeds were planted in one group.The hydraulic load of rainwater wetland is 40.0 L/(m~2·d)for 3 hours each time.The removal rate of total phosphorus in the effluent of rainwater wetlands with plants was 49.56%-71.09%,and that of rainwater wetlands without plants was 34.09%-79.36%.In most cases,the removal efficiency of rainwater wetlands with plants is better.When the influent ammonia nitrogen concentration was 20 mg/L,the removal rate of rainwater wetlands with plants was 87%-98.90%,and that of rainwater wetlands without plants was 86.86%-96.71%.The removal effect of rainwater wetlands without plants was better.When the concentration of nitrate nitrogen in influent water was 20mg/L,the removal rate of nitrate nitrogen in effluent of rainwater wetland with plant was 96.59%-98.60%,and that of rainwater wetland without plants was 98.55%-98.92%.The removal rate of nitrate nitrogen in effluent of rainwater wetland without plants was better.The removal rate of total nitrogen in rainwater wetland with plants was 85.93%-91.44%,which was lower than that in rainwater wetland without plants.The removal rate of total nitrogen in rainwater wetland without plants was very stable,which was 88.56%-93.06%.In addition,after 10 days of drought,the liquid level of plant reactor decreased by3 units,which total of 30 L,and that of non-plant reactor decreased by 0.5 units,which total of 5 L.Planting plants was better for rainwater wetlands to remove total phosphorus,but the attention of frequent water replenishment should be paid.