Transformation kinetics and pathways of sulfamonomethoxine by UV/H2O2 in swine wastewater

Abstract

Sulfamonomethoxine (SMM), as one of the most predominant antibiotics in animal wastewater, is pending for effective control to minimize its environmental risks. Transformation kinetics and pathways of SMM by UV/H2O2 in swine wastewater were systematically investigated in this study. Direct UV photolysis (as a dominant role) and ∙OH oxidation contributed to SMM degradation in UV/H2O2 system. The less effective reaction rate of SMM in real wastewater than synthetic wastewater (0.1–0.17 vs. ∼0.2–1.5 min−1, despite higher H2O2 dosage and extended reaction time) resulted mainly from the abundant presence of conventional contaminants (indicated by COD, a notable competitor of SMM) in real wastewater. SMM degradation benefited from higher H2O2 dosage and neutral and weak alkaline conditions. However, the effect of initial SMM concentration on SMM degradation in synthetic and real wastewater showed opposite trends, owning to the different probability of SMM molecules to interact with UV and H2O2 in different matrices. Carbonate had an inhibitory effect on SMM degradation by scavenging ∙OH and pH-variation induced effect, while nitrate promoted SMM degradation by generating more ∙OH. The removal efficiency of SMM in real wastewater reached 91% under the reaction conditions of H2O2 of 10 mM, reaction time of 60 min, and pH 6.7–6.9. SMM degradation pathway was proposed as hydroxylation of benzene and pyrimidine rings, and secondary amine, and the subsequent cleavage of S–N bond.