Media Cation Exchange Capacity (CEC) as a Predictor of Dissolved Copper Sorption in Biofiltration

Abstract Submission: Engineered media in stormwater biofiltration are designed to address water quality objectives. The effectiveness of biofiltration for specific contaminants is often tied to specific media types or media amendments, making it challenging to replicate successful performance when the exact media are unavailable. Our study aims to identify key measurable properties of media that influence the treatment of stormwater contaminants. Dissolved copper (Cu), removed mainly through sorption in biofiltration, was chosen as the target contaminant. Physico-chemical properties of six media types, including ASTM-C-33 sand, three wood-derived biochars, a regenerated activated carbon, and a zeolite (in size fractions appropriate for applications in biofiltration) were comprehensively characterized. In batch experiments with Cu-spiked parking lot runoff, cation exchange capacity (CEC) was the media property mostly strongly correlated with the sorption affinity constant (R2 > 0.85), suggesting that Cu sorption may be estimated from media CEC; this hypothesis is supported by column experiments measuring the Cu breakthrough curves from four media mixes. The columns were designed to mimic field conditions in terms of vertical profile, runoff flow rate and composition, and inflow Cu concentrations. Breakthrough curves of outflow Cu concentrations matched estimates predicted from batch experiments, confirming that media CEC can predict the lifespan of columns for dissolved Cu treatment. Our study, exemplified by Cu, demonstrates that specific water quality objectives in biofiltration can be achieved by selecting the right media property, instead of the media type. Our study introduces an approach to designing biofiltration media that has the potential to significantly broaden media choices.

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