Experimental Research On The Riverside Bioretention For Treating Polluted River

Action Plan for Prevention and Control of Water Pollution proposed that by 2020, efforts should be made to eliminate unusable water bodies in the Yangtze River Delta. However, under high-density population and developed industries, the inflow rivers of Taihu Lake in the Yangtze River Delta are seriously polluted so far, most of them could not meet water quality standard. The main reason lies in the excessive nitrogen and phosphorus loading. Hence, it has great realistic significance to research a simple and efficient river water treatment technology.In this paper, the bioretention was used to treat river water. According to the water quality and hydrological characteristics of rivers flowing into Taihu Lake, the bioretention was used to optimize the removal of nitrogen and phosphorus. Then, a feasible engineering design plan was presented. The main conclusions include:(1) The bioretention with activated carbon has the highest removal of nitrate (93-96%) compared with surfactant-modified activated carbon (SMAC), surfactant-modified zeolite (SMZ), zeolite, flyash and ceramsite. Although the SMAC could adsorb the most of nitrate, it would inhibit the growth of denitrifying bacteria, which leads to the bioretention with SMAC is similar to traditonal bioretention's removal of nitrate (49-66%).(2) The nitrate and total nitrogen concentrations of the bioretention with activated carbon would decrease with the increase of activated carbon height at the beginning, then they would keep stable; the removal of nitrate and total nitrogen would decrease with the increase of hydraulic loading; the activated carbon height and the hydraulic loading only have low impact on the removal of ammonia, total phosphorus and permanganate index. The best activated carbon height is 150mm, the best hydraulic loading is 4L/h. Under these conditions, the effluent quality could reach Class ? when the influent water quality is below Class V. and the total nitrogen concentration could meet the water quality standard of inflow rivers of Taihu Lake in 2020.(3) The combination of submerged and non-submerged zones in a bioretention could improve the removal of nitrate, ammonia, total nitrogen, total phosphorus and permanganate index, especially the total phosphorus. It could also prevent the deterioration of effluent quality at the beginning. Under these conditions, the best hydraulic loading would improve from 4L/h to 8L/h, the effluent quality could reach Class ? when the influent water quality is below Class V, and the total nitrogen concentration could also meet the water quality standard in 2020.(4) A bioretention is designed to treat a river which has 7.2m width,1.15m depth, and 0.01m/s flow rate. Under the conditions of the influent quality below Class V (the concentrations of nitrate, ammonia, total nitrogen, total phosphorus and permanganate index are respectively 4mg/L,2.4mg/L,8mg/L,0.4mg/L and 8mg/L) and 0.19m/h hydraulic surface loading, the floor space of the bioretention is 2539m2 and the operating cost is about 168000 yuan per year. The bioretention has advantages in the desired treatment effect and the floor space compared with the constructed wetland.