Field evaluation of highway runoff pollutant removal efficiency using compost filter media

Highway runoff is well recognized as containing a host of heavy metals that may degrade water quality. This awareness has driven attention towards management strategies capable of attenuating the transport of heavy metals to nearby water bodies. Composted biomass has been shown to have the ability to retain common highway runoff pollutants which, in combination with its low cost and abundant supply, has led to interest in its use as a filter material. Addressing the need for validation of this concept, three different models of commercially available Filtrexx® compost filter socks were assessed for heavy metal and total suspended solids (TSS) removal efficiency. The filters each contain a mixture of municipal compost from two Canadian cities and were installed in series as a treatment train adjacent to a busy section of highway 401 in southern Ontario, Canada. Results from a runoff event demonstrate removal efficiencies for the treatment train ranging from 15.5% (nickel) to 93.6% (chromium). Inflow concentrations of cobalt, cadmium, copper and lead exceeded Ontario Provincial Water Quality Objectives (PWQO). Outflow concentrations of these four metals were reduced to below their respective PWQO after passing the three filters. Each consecutive filter also reduced TSS concentrations, with an event average removal efficiency of 69% for the treatment train as a whole.