ENHANCED STORMWATER CONTAMINANT REMOVAL USING MODIFIED SORBENTS IN TREE FILTERS

Stormwater runoff, particularly in urban areas, contains several groups of contaminants that negatively impact surface- and groundwater quality if left untreated. Contaminants in runoff are often addressed by structural best management practices (BMP) that capture and treat runoff before discharging it. Many BMPs, such as tree filters, act as primary filtration devices that attenuate total suspended solids, nutrients, and heavy metals from runoff; but typically these BMPs are not designed to treat bacteria and have only minor petroleum hydrocarbon (PH) treatment capabilities. To address this shortcoming, two materials (red cedar wood chips, expanded shale) were modified with either Quaternary Ammonium Silane (QAS) or Silver Nanoparticles (AgNPs) to provide antimicrobial properties to the matrix and/or exploit their affinity to sorb PH, particularly polycyclic aromatic hydrocarbons (PAH). Results show that of the two materials investigated, wood chips exhibit the highest sorption capacity for QAS, making this material favorable for treating bacteria, while at the same time attenuating PAHs and metals by sorption processes. In case of AgNP amendments to wood, less QAS uptake and more desorption from the wood matrix was observed. Relative to wood, expanded shale exhibited less affinity for QAS and AgNP. Batch isotherm studies show that PAH, metal, and bacteria removal is higher with QAS amended wood chips than with AgNP amended wood chips. In this presentation, the contaminant removal efficiency of all modified and unmodified materials will be discussed on the background of how these materials may find use in enhanced treatment of stormwater in tree filter BMPs.