Comparison of the effectiveness of UV, UV/VUV photolysis, ozonation, and ozone/UV processes for the removal of sulfonamide antibiotics

Abstract

UV (254 nm) and UV/VUV (254/185 nm) photolysis, ozonation, and O3/UV combination were investigated and compared for the transformation of two sulfonamide (SAs) antibiotics, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP). Change in toxicity, the effect of bacteria growth inhibition of the treated solutions, and the cost-efficiency of the methods were studied. In UV/VUV radiated solutions, the formation of •OH results in the doubled transformation rate. The relative contribution of various ROS (•OH, 1O2, O2•−) to the transformations were also investigated in the case of UV and UV/VUV photolysis. Both SAs can be eliminated ten times faster during ozonation than UV photolysis; but conversion via ozonation is associated with the formation of products with low reactivity to ozone and has biological effects. The O3/UV process did not enhance the transformation rate but positively affected mineralization and significantly decreased the ecotoxicity of the treated solutions. Ozonation was cost-effective, but O3/UV is a much safer technology to minimize environmental impacts because it effectively reduces the ecotoxicity and the bacterial growth inhibition effect of the treated solution. The observed differences between SMT and SMP are primarily related to the transformation of the N-containing rings. Our results showed a correlation between the reactivity of the N-containing groups of SAs, the rate of mineralization, and the change in ecotoxicity and antibacterial effect and emphasized the need for toxicological characterization of the treated samples. The removal of parent compounds is not sufficient to avoid the release of toxic substances into the environment.