Research On Oxidation Of Sulfamethoxazole In Aqueous Solution Via Persulfate Activated With Typical Transition Metal Ions

Sulfamethoxazole (SMX) is a nonbiodegradable antibiotic,long-term exposing low concentration of SMX in water will make microorganisms resistant to it, which will endanger human health. Conventional process can not completely remove SMX from aqueous solution.Therefore, it is necessary to develop an economical and feasible technology for SMX treatment.Five different transition metal ions and their combination with hydroxylamine hydrochloride were chosen to activate peroxymonosulfate (PMS). Sulfate radical SO4-·, an active species to oxidize SMX, was produced during the process. The single activated experiments of PMS showed Co2+ and Fe2+ had a better activation performance, and the activation rate of PMS reached 78% and 51%, respectively. The joint activation experiments showed Co2+/NH2OH and Fe2+/NH2OH exhibited a higher performance, and the activation rates were 81% and 91%,respectively. Hence,Co2+,Fe2+ and Co2+/NH2OH,Fe2+/NH2OH were selected to activate PMS for SMX oxidation.The oxidation of SMX in different activated systems, including PMS, PMS/Co2+,PMS/Fe2+, PMS/Co2+/NH2OH and PMS/Fe2+/NH2OH system, indicated that PMS activated via separate Co2+ and Fe2+/NH2OH joint activation oxidizing SMX had high SMX degradation capacities. The removal rates of SMX in the two activated systems could reach 62% and 52%, respectively. Furthermore, the effects of temperature, pH, PMS concentrations,SMX concentrations, NH2OH concentrations, Fe2+ concentrations, different coexistence substances in water on oxidation performance of the two systems were investigated.In PMS/Co2+ system, the treatment efficiency of SMX increased with its own concentrations reducing and PMS concentrations increasing. Due to thermal-activation of PMS, the amount of So4-· increased, so, the removal efficiency of SMX increased with temperature increasing. Removal rate of SMX reached 94% at 55 ℃. As pH increasing from 3 to 9, SMX removal rate decreased from 62% to 23%. While pH=11, SMX removal slightly increased with SO4-· increasing by alkali-activated PMS. The presence of humic acid and anions (Cl- and HCO3-)in water reduced the degradation of SMX to a certain extent. In addition, analysis experiments of radicals indicated there were two kinds of radicals, SO4-·and -OH, in the system, but the main radical for SMX oxidation was SO4-·.In PMS/Fe2+/NH2OH system, removal efficiency of SMX increased with its own concentrations decreasing and PMS concentrations increasing. SMX degradation rate gradually increased with NH2OH concentrations increasing within a certain range. While NH2OH concentration is enough, the removal of SMX increased from 39% to 77% with Fe2+concentration increasing from 5μM to 12.5μM, when Fe2+ concentration increased to some extent, the degradation rate of SMX would not increase affected by hydroxylamine concentration. Due to thermal-activation of PMS, the amount of SO4-· increased,so the removal efficiency of SMX increased with temperature increasing. As pH increasing from 3 to 11, SMX removal rate decreased, due to the presence form of hydroxylamine and different presence of Fe3+/Fe2+. The presence of humic acid and anions (Cl- and HCO3-) in water reduced the degradation of SMX to a certain extent. In addition, analysis experiments of radicals indicated there were two kinds of radicals, SO4-· and ·OH, in the system, but the main radical for SMX oxidation was SO4-·, and benzoic acid added into the PMS/Fe2+/NH2OH system could inhibit the degradation of SMX.Removal rates of SMX from filtrated Songhua River by PMS/Fe2+/NH2OH and PMS/Co2+ were 4% and 93%,respectively,which confirmed the high efficiency PMS/Co2+system to remove contaminants in aqueous solution. Furthermore,removal efficiency of SMX from sewage secondary sedimentation tank effluent showed that both systems had a certain removal efficiency of SMX, the efficiency were 32% and 50%, respectively. It could be seen increasing the dosage of activator in the PMS/Fe2 /NH2OH system appropriately could promote the degradation of pollutants. Considering the toxicity of Co2+, it is feasible to use PMS/Fe2+/NH2OH system as an alternative advanced treatment technology to control SMX pollution in the water.