Comparison of sorptive filter media for treatment of metals in runoff

Rainfall runoff and snowmelt impacted by anthropogenic activities can transport significant loads of metals. Ecological concerns and recent regulatory guidance have spurred development of unit operations such as ex situ sorptive filters and engineered media infiltration systems with the intent of including sorption mechanisms for metals as compared to conventional filter media. Applications of sorptive media for rainfall or snow unit operations include infiltration systems, sorptive clarifiers, separation systems, and deformable, cartridge, or tubular filters. Column breakthrough experiments were conducted for selected sorptive filter media and compared to conventional filter media. Comparing plain sand, granular activated carbon, and cementitious media to oxide coated/admixture media, manganese oxide coated media (MOCM) had the best overall operational behavior with 10% breakthrough bed volumes (V-h), breakthrough capacity (X/M-b), and exhaustion capacity (X/M-exh) two times higher than those of iron oxide coated sand (IOCS). As the empty bed contact time (EBCT) for MOCM increased from 0.5 to 1.1 min; the values of V-b, X/M-b, and X/M increased by a factor of 2. Compared to metal breakthrough for uncoated sand or polymeric media, manganese oxide polymeric media (MOPM) as well as bench scale partial exfiltration reactor media (combining uncoated cementitious media and oxide coated media) provided significant capacities for Pb, Cu, Cd, and Zn. Removal mechanisms for MOCM include adsorption, surface complexation, ion exchange, and filtration, accounting for MOCM's high capacity. Although uncoated cementitious media also had a significant capacity for metals through precipitation and filtration, breakthrough instability of metal precipitates and high effluent pH can limit application in monomedium applications.