Stormwater runoff acts as a nonpoint source of groundwater pollution in urban areas, where it mobilizes trace contaminants from impervious surfaces, agricultural and recreational environments. Traditional infiltration systems designed to promote groundwater recharge are not equipped to remove these contaminants. Low cost geomedia can augment stormwater infiltration systems to passively treat contaminants in urban runoff prior to groundwater recharge. Functionalized organoclay composites, which take advantage of the high surface area and cation exchange capacity of inexpensive, naturally abundant clays, can be an ideal candidate for stormwater geomedia. To determine the feasibility of organoclay geomedia for stormwater treatment, polydiallyldimethylammonium chloride (pDADMAC)- and poly(4-vinylpyridine-co-styrene) (PVPcS)-coated montmorillonite composites were synthesized and characterized under simulated stormwater conditions. Seven representative trace metals and eight trace organic contaminants in urban runoff were used to assess the adsorption capacity of the composites and biochar, an alternative commercial engineered adsorbent, in batch adsorption and column filtration studies. The extent of contaminant adsorption was a function of contaminant and adsorbent surface charge, hydrophobicity, functional groups, and natural organic matter (NOM) content. For example, fouling by NOM decreased the adsorption of all contaminants on biochar; yet, enhanced removal of non-ionic and cationic trace metals and organic contaminants was observed for the clay composites. This effect was pronounced for pDADMAC composites due to permanent positive charge attracting negatively charged contaminant-complexed NOM. Biochar columns exhibited slower breakthrough for all organic contaminants, whereas trace metal breakthrough was slower in clay composite columns. Results indicate that while slow breakthrough occurs in biochar columns, biochar-amended infiltration systems may induce clogging and decrease stormwater permeability due to lower hydraulic conductivity compared to clay composite and control columns. Our findings suggest that polymeric organoclay composites can be a promising geomedia for trace metal adsorption in runoff to complement biochar and other geomedia for improved urban stormwater treatment.

Polymeric functionalized clay composites for adsorption of trace contaminants in urban stormwater infiltration systems

255th National Meeting (2018)

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