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Description
Scientific studies conducted in the U.S. and worldwide have reported widespread occurrence of pharmaceuticals in treated drinking water, surface water, groundwater, wastewater treatment plant effluent and sludge, and animal manure. Sulfathiazole (STZ) and sulfamethoxazole (SMZ) are pharmaceuticals that are used for human and animal treatment and have been found widely throughout the environment at levels from 7 ng/L to 7.3 _g/L. In this research, the degradation of SMZ and STZ in aqueous solution by ozonation, ozone/UV, and H2O2/UV was investigated. The degradation process was investigated experimentally in a semi-batch reactor under various operation conditions, i.e. ozone gas dosage, H2O2 concentration and water quality in terms of varying bicarbonate concentration and pH. Both SMZ and STZ were successfully degraded by all of the treatment methods. The experimental results during ozonation revealed that as the influent ozone gas concentration increased from 0.9 -- 3.5 mg/L, the removal of sulfonamides increased. With bicarbonate levels ranging from 2 -- 20 mM, results showed that increasing the bicarbonate ion concentration acted as a promoter of ozone decomposition up to 4 mM for SMZ and 8 mM for STZ and then acted as a scavenger of •OH radicals which reduced the degradation rate of both SMZ and STZ. Varying pH levels from 2 -- 10 revealed that as the pH increased the degradation of SMZ and STZ increased. Results for ozonation and ozone/UV treatment of the sulfonamides followed similar trends, i.e., removal of target sulfonamides increased with increase in influent ozone gas concentration. However, ozone alone degraded the sulfonamides faster than ozone/UV. This is because the lamps used in this study emit UV light primarily at 350 nm and the decomposition of ozone may have not been enhanced; UV light absorption of ozone is known to be at a maximum at 254 nm. With H2O2 concentrations of 0.9 -- 11.7 mM, the H2O2/UV experiments revealed longer degradation times for both sulfonamides as compared to ozonation and ozone/UV. Similar to ozone, H2O2 absorbs UV light primarily at 254 nm, while the UV lamps used in this study primarily emitted UV light at 350 nm. Thus, the decomposition of H2O2 to •OH may have not been enhanced by the UV light. Based on the comparison of moles of oxidant required to degrade the sulfonamides, it was determined that ozone is the best treatment technique to degrade SMZ and STZ as compared to ozone/UV and H2O2/UV for UV light emitted primarily at 350 nm. With approximately 3 mg/L of influent ozone, ozonation required 10.4 moles of ozone to degrade a mole of SMZ. While ozone/UV treatment required 14.6 moles of ozone to degrade a mole of SMZ. For STZ the results are similar, ozone treatment required 10.5 moles of ozone while ozone/UV treatment required 16.4 moles of ozone to degrade a mole of STZ
