Adsorption mechanisms for in-situ eco-treatment of urban waters as influenced by non-equilibrium partitioning of heavy metals

Under conditions of low rainfall pH, low residence times ( τ sf ) and low alkalinity, urban storm water is capable of delivering heavy metals in a predominately dissolved form. Even with the entrainment and delivery of a wide gradation of anthropogenic solids, low residence times of less than several hours are not sufficient to partition the dissolved heavy metal fraction onto these solids. Therefore, in-situ eco-treatment systems that are loaded by storm water having a combined delivery and treatment residence time of less than several hours require treatment design that facilitates adsorption or partitioning of the dissolved heavy metal mass. This study examines the importance of temporal partitioning at short residence times (typically less than two hours) for eco-treatment of urban heavy metals. Results from field testing of a partial exfiltration reactor (PER), a source control eco-treatment system, designed to facilitate adsorption, indicates dissolved mass removal can exceed 80% on an event basis. With respect to source control design treatment of urban storm water there are a number of conclusions that can be drawn from this study.