Experimental study on rainfall-runoff pollutant reduction by urban green space

Based on the state that non-pointed pollution caused by urban rainfall-runoff was one of the major factors which led to urban surface water contaminated and ecology deteriorated, a soil aquifer treatment system was built to experimentally study the pollution reduction effectiveness of green space, and the impacts of land cover, influent concentration, soil depth, hydraulic loading rate and residence time were analyzed. The results exhibit that green space has a better and stabilized ability to reduce three representative urban rainfall-runoff pollution concentrations, which COD are 44.5, 144.3, 487.2 mg·L^-1, NH₄⁺-N are 4.27, 11.44, 36.61 mg·L^-1 and TP are 0.98, 2.85, 9.66 mg·L^-1, respectively, and with 8.15, 7.13 and 6.12 cm·h^-1 hydraulic loading rate, respectively. The pollution reduction rates of COD, NH₄⁺-N and TP by green space are 33.41%-37.14%, 58.74%-61.49% and 63.65%-67.08%, respectively. The effect of land cover to pollution reduction rate is not significant because of the limitation of oxygen and hydraulic residence time. When pollution concentration increases, the comprehensive pollution reduction ability of green space is kept in 50%-60%, with a little increased tendency. Pollution reduction process happens mainly in the upper layer of the green space soil with a depth of 50-70 cm.