Investigation into the influencing factors and adsorption characteristics in the removal of sulfonamide antibiotics by carbonaceous materials

Due to the extensive application of sulfonamide antibiotics for disease control on humans and livestock, the discharge of their residuals has caused serious pollution to the water environment. To mitigate this pollution, various types of carbonaceous materials have been used as adsorbents to remove antibiotics from water. In this study, adsorption characteristics of three sulfonamide antibiotics on four carbonaceous materials under complex conditions have been explored in terms of the cycle of adsorption, desorption, and re-adsorption processes, single and interactive effects of multiple influencing factors, kinetics, isotherms, and thermodynamics. Adsorption isotherms of the main substance (sulfamethoxazole) in the co-adsorption system were also analyzed to illustrate the competitive effects of coexisting substances (sulfamerazine and sulfamethazine) and the degree of competition. Results show that initial concentration, pH, and their interactions had significant effects on the adsorption process. The optimal combination of these factors was the initial concentration of 30 mg/L, pH value of 4.0, temperature of 298 K, and ionic strength of 0–0.1 mol/L. The adsorbed amount of SMX was the highest for four materials under the optimal condition (i.e., 91.51 mg/g for PAC, 258.7 mg/g for W-GAC, 184.7 mg/g for 3M-GAC, and 46.14 mg/g for GP). Adsorbents had great potentials to remove sulfonamide antibiotics after desorption, which is valuable for materials' reusability. In addition, the existence of competitive substances would not change the main substance's exothermic or endothermic properties. These results could help reveal the adsorption, desorption, and re-adsorption mechanisms of various carbonaceous materials under complicated situations and provide reference to identify the regeneration conditions of adsorbents as well as determine the levels of influencing factors to remove sulfonamides antibiotics from water.