Water treatment residual-coated wood mulch for addressing urban stormwater pollution

Innovative treatment materials and technologies are demanded to address urban stormwater pollutants that challenge traditional infrastructure. This study aimed to investigate adsorption behaviors of aluminum-based water treatment residual (WTR)-coated mulch for capturing representative runoff pollutants (i.e., P, Cu, Zn, and Pb) and evaluate its treatment performance in a filtration bed. Data from batch studies were fit using the nonlinear least square optimization technique. Adsorption kinetic data followed the pseudo-2^nd-order reaction patterns, while the adsorption isotherm data obeyed the Freundlich models. Model fitting passed the chi-square tests, as a statistical goodness-of-fit criterion, at a 90% confidence level. Column studies indicate that the WTR-coated mulch with a bed depth of 5.1 or 10.2 cm could effectively alleviate flow-weighted mean concentrations of these pollutants, with a minimal aluminum release, during treatment of the equivalent annual runoff in a typical U.S. Northeastern catchment. This study demonstrates that WTR-coated mulch is an effective and safe adsorbent media to tackle urban stormwater pollution. Practitioner points: Aluminum-based WTR-coated wood mulch can simultaneously and effectively capture representative metals and phosphate in urban runoff. The pollutant adsorption follows the pseudo-2^nd-order kinetic reaction patterns and the Freundlich isotherm model. WTR-coated mulch (5.1–10.2 cm bed depth) sufficiently treats the runoff generated annually in a typical U.S. Northeastern catchment. Higher and more reliable pollutant removals can be achieved with a greater bed depth of the coated mulch in a filtration bed. Aluminium release is minimal during application of the WTR-coated wood mulch.