Mixed-Media Filter System for Removal of Multiple Contaminants from Urban Storm Water: Large-Scale Laboratory Testing

Abstract

Urban storm water runoff consists of unacceptable levels of nutrients and heavy metals, and a mixed-media filter system is proposed to treat such storm water with multiple contaminants. In this study, a two-dimensional filter simulation test apparatus was constructed to examine the effectiveness of mixed media for the removal of multiple contaminants from synthetic storm water. The mixed media, selected based on several series of batch and column experiments in previous studies, consisted of a mixture of calcite, zeolite, sand, and iron filings. The mixed media was tested for removal of coexisting nitrate, phosphate, Ni, Cu, Cd, Cr, Pb, and Zn at concentrations and conditions relevant for typical urban storm water. Results show that the mixed-media filter was able to maintain high flow rates without any clogging issues, with an average hydraulic conductivity around 30 cm/min. No significant initial release or final desorption of the contaminants was observed. The filter system proved effective for the simultaneous removal of nutrients and heavy metals from the storm water, except for Ni, which had significantly lower removal efficiency than the other metals. Overall, the study indicated that a mixed-media filter can be designed with high contaminants removal capacity, but additional studies are recommended for evaluating long-term performance of the mixed-media filter under variable storm water field conditions.