Study On Composite Media Multilevel Filtration For Urban Stormwater Runoff

At present, water shortage, water pollution serious, and urban floods occur frequently are the main features of China’s water resources. These three features are both contradict and restraining each other, the best way to solve the contradiction between them is rainwater utilization reuse. With urban stormwater runoff recharge groundwater and depth reuse as a target for multi-stage filtration technologe research, according to the characteristics of urban stormwater runoff, mainly carried on the research from four aspects:the characteristics of heavy metals, nitrogen and phosphorus nutrients, organic matter(COD), polycyclic aromatic hydrocarbons(PAHs) dissolved ratio, concentration and rate from road-deposited sediment (RDS); the static adsorption effect of zeolite, ceramsite, slag, shell activated carbon, nutshell filter, coconut shell activated carbon for PO43-, ammonia nitrogen, nitrate nitrogen, COD, Cu, Cr, Cd, Pb in artificial preparated rainwater; the efficiency of five different schemes composite media multi-stage filtration technology for the removal of various pollutants in artificial preparated rainwater was studied, and according this put forward the media compound optimization way, its practical application was analysed through a case; from the objectivity of precipitation, the features of media, different rainwater recyling way assessment the reused risk of rainwater filtrated by composite media multi-stage thehnology, quantify the possible impact or losses bring by risk.The research results show that:the dissolved ratio of heavy metals, nitrogen and phosphorus nutrients, PAHs from RDS basically less than10%, so the pollutants in RDS mainly output for particles state, in other words, the pollutants dissolved vert little along with the rainfall; the RDS less than125μm is easily washed away by runoff, but it accounted for48%of the total RDS, and the heavy metals, nitrogen and phosphorus nutrients, COD dissolved concentration and rate are the biggest in this particle size range, so it is the key objects for removal; heavy metals, nitrogen and phosphorus nutrients, COD dissolved rate are very big within5min of the experiment beginning, but nearly for zero as follows, so when the initial split-flow measures are taken, the suspended solids retention by composite media will almost can’t release of dissolved contaminants; the static adsorption effect of six medias for the pollutants in artificial preparated rainwater show that, each media only for one or several kinds of pollutants has a better removal effect, through the media optimization, obtained the combination property order of each media as follows:coconut shell activated carbon> shell activated carbon> zeolite> nutshell filter> ceramsite=slag; by comparative analysis of five kinds of filtering schemes for the pollutants removal rate in artificial comparated rainwater, the filter media compound optimization method is given in the form of a flowchart, the application of this process is explained by a case study; the assessment of filter media characteristics indicate that, the rainwater purified by single meida cann’t achieve a variety approach of reuse; but the rainwater purified by composite media reuse to variety approach, can reach the intermediate risk; the assessment of rainwater reuse in different way show that, when the rainwater reuse for life miscellaneous and construct water landscape, the risk is very low; reuse for industial purpose and surface recharge and groundwater recharge, the risk level is intermediate.The research about characteristics of pollutants dissolved from different partical size of RDS provide a basis for urban road runoff total pollutant control, purification facilities research and development, the risk assessment of rainwater reuse; by the research of composite media multi-stage filtation technology, a filter media compound optimization method based on single media static adsorption performance is proposed, it provide a reference to carry out more extemnsive rainwater purification; the risk assessment model based on rainwater reuse after filtating by composite media multi-stage filtration technology can quantify the possible impact or losses bring by risk.