| Stormwater runoff pollutants are one of the main sources contributed to surface water pollution. Various pollutants in the runoff result in eutrophication, heavy metal and organic pollutions. The research of effective removal of runoff pollutants is of vital importance to stormwater management and control.Soil infiltration system is a traditional wastewater treatment technology, and pollutants can be removed in the physical, chemical and biological processes by interception, sedimentation, absorption, complexation and biological digestion. However, clogging in the traditional soil infiltration system occurs frequently. The main reason can be attributed to low infiltration of clay which has strong absorption for pollutants. Pollutants and metabolites of microorganisms get stuck in the clay with the long-time running.Polyurethane foam, artificial turf and leaf litters were used respectively in this research to improve traditional soil infiltration systems. The experiment was conducted using synthetic stormwater dosing into transparent columns filled with media. Pollutants removal ratios were compared in the improved soil infiltration systems under different pollution loads and runoff rates. The purpose was to improve the pollutant removal efficiency from runoff by improved soil infiltration systems. The research provided a new method for runoff pollution treatment, and improved soil infiltration systems could be applied to the engineering programs with high efficiency.The research included two parts. The first part was runoff pollution monitoring in Anhui University. Experiment was conducted by sampling in the Science and Technology Building, the Dining Hall of Post Graduates, and the Dormitory for Teachers representing working place, catering area and living district respectively. Samples of three rainfall events were analyzed in the laboratory to determine pollution characteristics and provide background statistics for further research. The second part was lab-scale simulations by controlling the pollutant concentrations and influent rates. Polyurethane foam improved soil infiltration system, artificial turf improved soil infiltration system and leaf litters improved soil infiltration system were constructed to treat synthetic wastewater and treatment efficiency was indicated by removal rates with the testing of pollutants concentrations in the effluent.The results of outdoor monitoring showed that the NH4+-N and TN in the runoff had achieved V level of environmental quality standards for surface water (GB3838-2002) and were the main form of nitrogen pollutants in the road runoff. By contrast, the amount of NO3--N and NO2--N was slight. NH4+-N and TN concentrations in the Dormitory for Teachers and the Dining Hall for Post Graduates were higher than the amounts in the Science and Technology Building with the contribution of proteins, sugars, fat and other organic pollutants in daily life and catering. Rainfall parameters had obvious influence on initial runoff pollution and long dry period and strong rainfalls deteriorated the pollution.Both systems had a relatively high removal rate in NH4++-N with the average removal rate of more than98%. The removal efficiency of NO3--N in polyurethane foam system and artificial turf system were poor in low pollution loads with the effluent concentrations higher than the influent concentrations indicating biological reactions of turning NH4+-N to NO3--N in the system.17.52%of NO3--N was removed from the polyurethane foam system only in high pollution load. NO2--N removal efficiency in polyurethane foam system was87.29%, higher than the value in artificial turf system with the removal rate of53.77%. The average TN removal rates in polyurethane foam system and artificial turf system were72.65%and71.07%respectively. Cu and Pb in effluent were not detectable indicating that Cu and Pb could be removed mostly in both systems. The Zn removed efficiency from artificial turf system was higher than the value from polyurethane foam system, and the average removal rates were90.04%and80.3%respectively. Polyurethane foam system, artificial turf system and leaf litters system had comparably good removal rates of TP and SS under different runoff rates. TP and SS removal rate in polyurethane foam system were87.04%and94.32%. Artificial turf system could remove89.07%of TP and82.78%of SS. The removal rates of TP and SS in leaf litters system were91.31%and87.71%. COD removal rates in all the improved systems were bad, and the highest COD removal rate was74.36%in polyurethane foam system. While the removal of COD in artificial turf system and leaf litters system were66.83%and56.40%respectively. Runoff rate was the main factor that influenced hydraulic residence time. The reaction process was restricted by short hydraulic residence time resulting in low removal rate.The results showed that the application of leaf litters could avoid water flushing and maintain stable water flow, and provide sufficient nutrients for microorganisms growth as well. Roots of artificial turf could promote the absorption of nitrogen, phosphorus and heavy metals and improved soil physical, chemical and biological environment. The addition of polyurethane foam could improve soil infiltration and increase oxygen amounts. Clogging occurred in the polyurethane foam system in the research and the possible reasons could be the insufficient amount of polyurethane foam and uneven dispersion of polyurethane foam in the soil which limited the effective functioning of the systems. Relative research was still to be done to further improve soil infiltration and pollutants removal rate. |
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