Occurrence And Degradation Mechanism Of Non-steroidal Anti-inflammatory Drugs In Sewage Treatment System—Diclofenac Represented

Non-steroidal anti-inflammatory drugs?NSAIDs?are used to treat fever,pain,inflammation and other diseases,which is one of the most widely used drugs in the world.There is about 30 million people used 500 million prescriptions per year.In many countries,NSAIDs were detected in sewage,surface water and groundwater.Although the concentrations of NSAIDs were at a trace level,they are still toxiced to aquatic organisms and posed a potential threat to the environment and human health.The Wastewater-based epidemiology?WBE?has become an important tool to complement traditional surveys,which can be used to investigate the consumption of illicit drugs and PPCPs by providing real-time variability data and assessing regional differences and seasonal trends.But the use of WBE research in China was almost none.Therefore,we selected NSAIDs as the research object and detected the concentration of NSAIDs in the influent of WWTPs and evaluated the consumption pattern of NSAIDs by WBE in order to explore the patterns of NSAIDs usage and regional differences.At the same time,Diclofenac?DCF?was selected as the representative of NSAIDs to carry out its adsorption behavior in various types of sludge as well as the degradation behavior under chlorine and UV disinfection.Related research findings are as following:?1?The concentrations of five NSAIDs?including paracetamol?ACM?,aspirin?AYS?,diclofenac,ibuprofen?IBU?,and naproxen?NAP??in influent samples from four WWTPs in Guangzhou and Zhuhai cities of Guangdong Province were N/A¹38.45 ng·L^-1,consistent with the data reported in previous publication in China,but much lower than that in developed countries.The mass loads of ACM(17430 mg·?d·1000 persons?^-1)were highest and the DCF mass loads(13.75 mg·?d·1000 persons?^-1)were the lowest.The per capita mass loads of NSAIDs in China were much lower than that of developed countries.The differences in their regional distribution were related to the health of people,living habits,economic development and traditional concepts.The seasonal changes of the mass loads of the five NSAIDs were different.The mass loads of ACM and IBU significantly increased in winter,while the mass loads of AYS,DCF and NAP were not significantly seasonal,which were related to the diseases they treated,such as colds,fever,arthritis,etc.?2?The adsorption process of DCF onto suspended particulate matter,secondary sedimentation tank sludge and concentrated sludge was a two-step process:a rapid adsorption process followed by a slow one.The adsorption capacity was related to the organic matter content and specific surface area of sludges.Adsorption kinetics followed the pseudo-second-order kinetic equation,indicating that the adsorption process was dominated by chemical adsorption and the adsorption reaction was the rate-limiting step of the entire adsorption behavior.The adsorption of DCF on the three sludges conformed to Linear model,Langmuir isotherm model,and Freundlich isotherm model,respectively.All of the adsorption reactions were spontaneous exothermic reaction.The adsorption capacity decreased with the increase of pH value.The increase of ionic strength enhanced the adsorption of DCF.The dissolved organic citrate decreased the adsorption capacity of DCF,urea had no effect on sludge adsorption to DCF.The desorption capacity increased with the increase of pH value.?3?The results showed that the degradation of DCF by sodium hypochlorite followed the second order kinetics.The pH value had an important effect on the oxidative degradation of DCF by NaClO,and had a good oxidative removal rate under acidic pH.When pH<5,the reaction rate constant was significantly increased.The removal rate of DCF increased with temperature increasing,which followed Van't Hoff rule.Furthermore,NO₂^-,NH₄⁺,HA,SDBS and Tween-80 showed significant inhibition to DCF chlorine oxidation with their content increasing.?4?Under UV irradiation,the kinetics of photodegradation of DCF followed pseudo-first-order kinetic,and photolysis rate decreased with the increase of DCF initial concentration.The photolysis of DCF included direct photolysis and self-sensitized photolysis of reactive oxides such as·OH,¹O₂ and O₂·.The photodegradation rate slightly increased with the increase of reaction temperature.The pH value affected the existence of DCF and the photodegradation rate decreased and then increased.Furthermore,Cl^-,Br^-,I^-,NO₃^-,NO₂^-,HA,SDBS and Tween-80 showed significant inhibition to the photodegradation of DCF with their content increasing.NH₄⁺had little effect on photolysis of DCF.