Sulfamethazine Adsorption Isotherms and Kinetics with Hypercrosslinked Polymer MN250 at Varying Ionic Strengths.

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 soil mobility, sulfamethazine contaminates groundwater and causes aquatic ecosystem damage. Current treatment methods to remove sulfamethazine are not universally effective, which necessitate newer remediation techniques. Hypercrosslinked polystyrene adsorbents show promise because of high surface areas, high mechanical strength, and regenerable properties. Using batch adsorption techniques, this study compared the capacity and rate of sulfamethazine adsorption onto Purolite hypercrosslinked adsorbent MN250 under conditions of varying ionic strength (KCL ranging from 0.005 to 0.5 M). The maximum adsorption capacity of MN250 for sulfamethazine (Qe) was 181.00 mg/g in 0.005 M KCl solution, which decreased 34% in 0.05 M KCL. In 0.5 M KCl, the maximum Qe value (153.4 mg/g) increased 26% over MN250’s capacity in 0.05 M KCl. The adsorption kinetics displayed prolonged adsorption over 144 to 168 hours at all concentrations, best fitting Ho’s pseudo-second order model. The decrease in capacity and kinetics from 0.005 to 0.05 M KCL is likely due to: (i) KCl ions interacting with charged or aromatic groups within the polystyrene polymer, which may alter sulfamethazine’s mechanism of adsorption (i.e., Van der Waal forces such as pyrimidine or aniline π-π interactions, hydrogen bonding, and/or electrostatic forces); and/or (ii) ions in solution are likely to create an electrical double layer at MN250’s polymer surface, depending upon the zeta potential of MN250, which decreases the activity coefficient of sulfamethazine. At ionic strengths simulating seawater (0.5 M), salting-out phenomena decreases sulfamethazine’s solubility, which acts as an additional driving force for sulfamethazine adsorption onto MN250. MN250’s high capacity for sulfamethazine adsorption across a wide range of ionic strengths highlights its potential for groundwater remediation.