Removal of Sulfamethazine By Hypercrosslinked Adsorbent MN250 in Simulated Groundwater.

Four hundred tons of sulfamethazine are fed to livestock annually in North America to prevent disease and promote growth, but most of the drug is excreted unmetabolized into the environment. Due to slow degradation and high mobility, sulfamethazine contaminates groundwater and causes aquatic ecosystem damage. Current water remediation methods have limitations, which necessitate newer techniques. Hypercrosslinked polystyrene adsorbents show promise because of high surface areas, high mechanical strength, and regenerable properties. Using batch adsorption techniques, this study investigated the capacity and rate of sulfamethazine adsorption/desorption with Purolite MN250 in both distilled water and simulated groundwater containing dissolved minerals and tannins. In distilled water, sulfamethazine adsorption onto MN250 displayed an L-class isotherm consistent with monolayer adsorption, negligible solute—solute interactions at the adsorbent surface, and decreasing activation energies of desorption with increasing surface coverage. MN250 had a maximum capacity of 111 mg g^-1 (C_e = 15.4 mg L^-1), highly correlated to the Freundlich model. Adsorption equilibrium was attained at 59 hours, correlating to Ho’s pseudo-second order model. Sulfamethazine minimally desorbed in distilled water. With common groundwater ions or dissolved humic acid, MN250’s adsorption capacity was 88.8 mg/g (C_e = 15.0 mg L^-1) and 109.3 mg/g (C_e = 11.5 mg L^-1) respectively, both correlating to Langmuir’s model. Groundwater ions and humic acid prolonged equilibration to 99 hours and 138 hours respectively, with kinetics correlating to Ho’s pseudo-second order model. With groundwater ions, the adsorption capacity decreased by 20% and equilibration was prolonged due to ions interacting with MN250 and/or sulfamethazine. Dissolved humic acid increased the capacity by 14% and prolonged equilibration, likely due to humic acid acting as a carrier for sulfamethazine adsorption while also delaying intraparticle diffusion. MN250’s high capacity for sulfamethazine adsorption, minimal desorption and regenerable potential make it a practical alternative for sulfamethazine removal in areas with contaminated groundwater.