Study On The Transformation Efficiency Of Typical Pharmaceuticals In Water By Emerging Characteristic Free Radicals Based On UV Induction

Pharmaceuticals and personal care products(PPCPs)are one of the most frequently reported emerging contaminants in the world.Numerous studies have confirmed their potential adverse effects on humans and animals,showing teratogenic,mutagenic,carcinogenic and reproductive developmental toxicity.In this paper,trimethoprim(TMP)and iohexol(IOH)were selected as the research objects.The degradation characteristics,cost-effectiveness,degradation pathways and the production potential of disinfection by-products(DBPs)of TMP and IOH in water by reactive chlorine species(RCS)(UV/NaClO2)and sulfate radical system(UV/PS)based on UV-induced emerging characteristic radicals were investigated.To provide theoretical and technical support for solving this problem in sewage treatment plant.Due to the endogenous free radicals HO· and RCS(Cl·,CIO·)in the system,the UV/NaClO2 combined process can remove TMP faster than UV photolysis or chlorite oxidation alone.The second-order reaction rate constants of TMP with Cl·,ClO· and ·OH were 1.75 ×1010,1.3 × 109 and 8.66 × 109 M-1 s-1,respectively.Under the effect of UV/NaClO2 combination process,the degradation rate of TMP under acidic condition is much higher than that under alkaline condition.The presence of Cl-significantly promoted the UV/NaClO2 degradation rate of TMP,while HCO3-and NOM had inhibitory effects.The optimal condition for TMP degradation in UV/NaClO2 system is that the optimal dose of NaClO2 is 1000μM when the UV intensity is 2.43 mW cm-2.In the subsequent disinfection,the overall weighted toxicity assessment was UV/Cl2>UV/NaClO2>UV/ClO2.Due to the important role of active chlorine in the system,the TMP degradation efficiency of UV/NaClO2 is much higher than that of UV/ClO2,and the toxicity is much lower than that of UV/CIO2.UV activated PS process can remove IOH faster than UV photolysis or PS oxidation alone.In UV/PS system,·OH and SO4·-were the main reactive radicals,and the contribution of SO4·was dominant.The kapp of·OH and SO·4·-with IOH were 1.01 ×1010 M-1 s-1 and 1.29×1010 M-1 s-1,respectively.Under the effect of UV/PS combination process,the degradation rate of IOH was the best under neutral conditions,and was inhibited under acidic and alkaline conditions.Cl-,NH4+and NOM inhibited the degradation of IOH,HCO3-and SO42-had no significant effect on the degradation of IOH.The optimal condition for IOH degradation in UV/PS system is that the optimal dose of PS is 200 μM when the UV intensity is 9.76 mW cm-2.In summary,the emerging characteristic radical RCS system(UV/NaClO2)and sulfate radical system(UV/PS)can not only efficiently remove PPCPs,but also have the potential for water toxicity risk control.Chlorite is a raw material for the production of chlorine dioxide.It is directly used in water systems and has high cost-effectiveness control potential.It has obvious advantages over the advanced oxidation process of HO·.In this study,the RCS system and sulfate radical system were deeply explored through degradation characteristics,costeffectiveness,degradation pathways and related toxicity assessment of DBPs,which provided a theoretical basis for the practical application of water treatment processes,and was conducive to effectively reducing water quality risks and promoting the further development of water quality science.