Study On Sulfamethoxazole Degradation By Ultrasound/Ozone Oxidation Process

Nowadays, people’s demanding on environment is rising with the development ofliving standard. Contaminations of natural waters by antibiotic pharmaceuticals areregarded as a rising issue of global concern. The abuse of antibiotics has caused a seriesof environmental problems on the water resources of the world that cannot be ignored.It is, therefore, important to develop efficient and economic treatment techniques tolimit the presence of antibiotics in aquatic environments.In this study, sulfamethoxazole (SMX) degradation was investigated usingultrasound/ozone oxidation process (UOOP). It was proved that the ultrasound didenhance ozonation for SMX degradation. The influencing factors of ozoneconcentration, pH, initial SMX concentration, ultrasound power density and radicalscavenger were studied. The results indicated that SMX degradation followed apseudo-first-order kinetic model under experimental operating conditions. SMXdegradation rate atincreased with increasing ozone concentration, pH and ultrasoundpower density and was inversely proportion to the initial SMX concentration. At thesame time, the optimum operation condition is found at ozone concentration4g/h, pH9,initial SMX concentration50mg/L and ultrasound power density800W/L, respectively.Meanwhile, after60min treatment, the COD was removed by80%and thebiodegradability (BOD5/COD ratio) increased from0to0.54. And the biologicaltoxicity of the intermediates decreased from100%to18%.The degradation mechanism of SMX and the strengthening mechanism ofultrasound were also determined in this research. It was proved that ultrasoundsignificantly enhanced SMX ozonation by assisting ozone in producing more hydroxylradicals in UOOP so that improving the oxidation rate and saving investments andoperation costs. The reaction rate constants were also compared between ozone-aloneand UOOP system. The results demonstrated ultrasound also made the rate constantsimprove by kinetics analysis. When ultrasound was added to the ozonation process, thereaction rate increased by6%-26%under different pH conditions through the ozonedirect and indirect oxidation ways.Moreover, main intermediates oxidized by US, O3and UOOP system wereidentified. Although the main intermediates in ozonation and UOOP were similar, theintroduction of ultrasound in UOOP had well improved the cleavage of S–N bond. Inthis condition SMX become much easier to be attacked, which led to enhanced SMXremoval rate in UOOP compared to the other two examined processes. Finally, the SMXdegradation pathways were proposed.