Studies On Pollutant Reduction Of Storm Water Runoff Through Topsoil

Along with the urbanization process accelerating, proportion of hardening surfaceincrease rapidly, infiltration quantity of road surface runoff rainwater decrease greatly,cause the ground water level losing, at the same time brought the city waterloggingdisasters; Due to the traditional drainage system, peripheral water eutrophicationphenomenon more and more serious. In the long run, that played a blocking effect to theurban economic and social development. Urban greenbelt as an important part of urbanecological system, use plant and soil layer to reduce runoff pollutants is a kind of lowcost, natural environment, a long-term ecological value method.Based on the consult and summarise for the control and treatment methods ofrunoff from cities at home and abroad, through the analysis and investigation for thesurface runoff of rainwater different seasons in xi ’an, combined with the indoorsimulation test, studies the surface soil and soil containing vegetation in the northwestregion of urban surface runoff pollution purification and adsorption rule and runoffpollutants make impact on soil surface basic physical properties, discusses thefeasibility and value about the low potential green space as flood control system of xi"an, at the same time provide theoretical basis for planning and construction in xi ’ancity garden and green space system.The results showed that: Temperature and underlying surface have a great effect onrunoff quality quality. In the summer, rain water quality is bad, especially initial stage.The mainly concentration of pollutants in runoff is beyond the water reuse, in addition,the runoff of BOD5, COD ratio of0.3or less, the biochemical degradability is low. So,the ground runoff rainwater is not suitable for direct reuse.The treatment effect of soil on runoff rainwater is idealization, the removal rate of COD, TP, TN, NH4+-N, NO3--N respectively by surface soil is:44%~70%,41%~74%,74%~51%,40%~85%and46%~56%. the removal rate of COD, TP, TN, NH4+-N, NO3--N respectively by soil with vegetation is:47%~88%,46%~86%,86%~62%,45%~86%and42%~56%.planting vegetation on the soil can remove the pollutants in the runoff preferably,and the alter condition of basin cushion is better than bare soil. The mainly pollutantremoval mechanism of soil layer is soil retaining effect, and the role of the adsorption ofpollutants on soil and plant root absorption on secondary status. Urban greenbelt andurban garden is economic and practical methods which can regulate flood better, thepollutant removal effect is more apparent, it can be used widely in future planning anddesign.The storm runoff will produce a certain impact on the physical properties of thesoil in the process of penetration, the soil moisture content and porosity declineobviously, but the bulk density rise, soil become more compact, which is the reason ofwhy the pollutant reduction increased of soil to the final phase. Planting vegetation onsoil has a strong effect on the absorption of nutrients, additionally, root system boundtogether, storm runoff pollutants removal effect is better.The adsorption time about topsoil for various pollutant is2h~2.5h, commonlyadsorption rate is larger within0.5h, the soil for different concentrations of pollutantsadsorption equilibrium time does not change along with the change of concentration,but the equilibrium adsorption quantity showed increasing trend with the increase ofconcentration.