Studies On The Degradation Of Nonsteroidal Anti-Inflammatory Drugs At Environmental Concentration In Wastewater By UV/Na₂S₂O₈

Nonsteroidal anti-inflammatory drugs(NSAIDs)is a kind of anti-inflammatory drugs without steroidal structure,and is also a kind of emerging contaminants.Nonsteroidal anti-inflammatory drugs(NSAIDs),especially diclofenac(DCF),ibuprofen(IBP)and naproxen(NPX),are reported frequently in the effluent of wastewater treatment plants(WWTPs)in China.NSAIDs presented in aquatic environment with low concentration and perdurability,with potential adverse effects on aquatic organisms.Especially,the synergistic effects of various NSAIDs on aquatic organisms will be more significant.Due to the incomplete removal of NSAIDs in WWTPs,NSAIDs enter the aquatic environment with the discharge of wastewater.Therefore,the advanced treatment of effluent is necessary.UV//Na2S2O8(UV/PS)is a new advanced oxidation process(AOP)based on sulfate radical(SO4-')and it is efficient in disposing refractory pollutants.Whereas,the mechanisms on UV/PS degradation of NSAIDs in wastewater disposal remains unclear.This study investigated the degradation kinetics,degradation mechanisms,and major influencing factors in the process of UV/PS degrading NSAIDs(mixed solution of DCF,IBP and NPX at environmental concentration(?g/L)).Besides,the toxicity effects of UV/PS degradation products(DPs)of NSAIDs on Cyprinus carpio(C.carpio)were also studied.The results of this study could contribute not only on the development of NSAIDs advanced treatment technology,but also on the ecological risk control of NSAIDs.The main findings are as follows:(1)The results on degradation kinetics of the three NSAIDs by UV and UV/PS:The results UV photolysis indicated that the order of photolysis rate was DCF>NPX>IBP.The removal of DCF,NPX and IBP improved evidently when combined UV with PS,and the degradation of DCF,NPX and IBP in the UV/PS system could be described by pseudo-first-order kinetic equations.Besides,the removal of NSAIDs increased with the increase of PS dosage.(2)The results on degradation mechanisms of NSAIDs in UV/PS process:The radical inhibition experiments showed that,SO4-· played a major role(>50%)in the UV/PS process,followed by-OH,and the direct photolysis was least important(<10%).DCF is more inclined to be photolized than NPX and IBP,thus DCF can still achieve high removal through direct photolysis when radicals are inhibited.The TOC removal was only 20%when the removal of the three NSAIDs reached 90%.The low removal of TOC indicates DPs were generated in the degradation of NSAIDs,and the DPs were hard to be mineralized.According to the DPs detected by LC/MS,it can be concluded that decarboxylation and hydroxylation reactions are main degradation pathways of the three NSAIDs.Dechlorination under the attack of hydration electrons is also a degradation pathway in the degradation of DCF.The hydroxylated products have higher intensity in DPs of IBP,whereas the decarboxylated products have higher intensity in DPs of NPX.(3)The results on UV/PS degrading NSAIDs in different secondary effluents:In pure water,when the initial concentrations of PS and NSAIDs were 10?M and 0.1 ?M,the removal of DCF,NPX and IBP reached 97%,95%and 88%,at 300 s respectively.However,under the same initial reaction conditions in secondary effluent,the removal of DCF,NPX and IBP were only 19%,10%and 2%,respectively.The removal of NSAIDs in effluent were significantly lower than those in pure water,which indicates that it was the constituents in secondary effluent that inhibited the efficiency of UV/PS.The degradation of NSAIDs by UV/PS in different effluents was studied further,and concluded that the removal of IBP fluctuated greatly,with the lowest being 37%and the highest being 81%,and the removal of DCF and NPX were all above 70%.The influences of humic acid(HA),alkalinity(HCO3),nitrate(NO3)and chloride(Cl-)on the efficiency of UV/PS were studied.The results showed that HA and HCO3 had significant inhibitory effects on UV/PS efficiency.While NO3-,Cl-had no significant effect.(4)The results on the toxicity of UV/PS DPs of NSAIDs on C.carpio:The acute toxicity of NSAIDs to luminescent bacteria increased after UV/PS treatment,indicating that the UV/PS DPs of NSAIDs are more toxic than the parent compounds.When C.carpio exposed to 0.1 ?M NSAIDs(Group 1),10 ?M PS(Group 2),0.1 p.M NSAIDs treated by UV/PS for 300 s(Group 3),and 0.1?M NSAIDs treated by UV/PS for 1800 s(Group 4)for 96 h,respectively,all experimental groups showed elevated protein levels,inhibited antioxidant enzymes(superoxide dismutase,catalase,glutathione peroxidase)activities,and increased lipid peroxide(malondialdehyde)content,and the order of toxicity of experimental groups was:Group 4>Group 3>Group 2>Group 1.When compare Group 3 or Group 4 with the blank group,there were significant differences(p<0.05)in terms of protein content,antioxidant enzymes activities,and lipid peroxide content.Results of the time dependent effect showed that the oxidative damage was observed when C.carpio exposed to 0.1 ?M NSAIDs DPs for 48 h,and the damage was continuously enhanced with the prolonged exposure time.UV/PS cannot completely remove the DPs of NSAIDs,and the DPs have potential ecological risks.Therefore,it is necessary to optimize the UV/PS reaction conditions to improve the removal of NSAIDs and the ecological safety of UV/PS.