Filtration Treatment of Pollutants in Urban Runoff Using Expanded Polypropylene Media

摘要

Pollutants such as heavy metals and PAHs (Polynuclear Aromatic Hydrocarbons) in stormwater runoff are a major problem in urban areas because these pollutants are discharged directly, in most cases without any treatment, into the receiving environments like river and lake. Since many of the pollutants are associated with suspended particulate materials in stormwater, SS (suspended solids) is of acknowledged importance in stormwater runoff treatment by BMPs (best management practices). Filtration, which is commonly used for removing particulate matter in stormwater structural BMPs, depends on various factors (e.g., filter media size, flow rate, bed depth, filter surface properties, etc). Especially, the characteristics of filter media are important factor affecting removal efficiency of pollutants and replacement period of filter media in filtration performance. In this study, EPM (expanded polypropylene media) as a filter media was manufactured at different expansion ratios (i.e., 5, 10, 15 times) and tested in the up-flow filtration for removing pollutants in urban stormwater runoff. The specific surface area of EPM_(10), EPM_(15), EPM_(30), EPM54 was 0.760 m~2/g, 0.799 m~2/g, 0.812 m~2/g, 0.845 m~2/g, respectively. The SS removal efficiency (64.1%) by EPM media was higher than that (44.2%) by sand media. In case of EPM_(10) media, it took 175min of removal rate of filtration system to be approached under 50% and EPM_(15) media was spent 110min. However, the SS removal efficiency of EPM 15 was over 10% higher than that of EPM_(10). The COD_(Cr) removal efficiency of EPM media was also increased with increasing expansion rate. The experimental results in this work show that pollutant removal efficiency by EPM media was increased with increasing expansion ratio but replacement period of media was decreased. EPM media are expected to adsorb non-biological organics like PAHs owing to its hydrophobicity.