Study On The Degradation Mechanism Of Chloroquine Phosphate In UV/chloramine Syste

At the beginning of 2020,when the novel coronavirus epidemic broke out worldwide,a large number of antiviral drugs such as chloroquine phosphate(CQP)were used for the treatment of patients infected with COVID-19.Due to incomplete digestion of patients and improper waste treatment,antiviral drugs and their metabolites could enter the urban sewage system through human excretion,medical wastewater and other ways,leading to increased concentrations of drugs in the sewage system;Since traditional sewage treatment plants cannot effectively remove COVID-19 therapeutics such as CQP in sewage,the residual antiviral drugs in water pose high risks and ecotoxicological risks to aquatic organisms,so the removal of antiviral drugs cannot be ignored.At present,there are few researches on the effective degradation technology,degradation pathways,migration and transformation,and ecological toxicity of CQP.It is necessary to develop appropriate treatment technology to solve the ecological environmental security problems caused by CQP pollution in water sources.In addition,chloramine disinfection has the advantages of low tendency to produce disinfection byproducts and long disinfection time.When combined with UV,it produces · OH,active chlorine free radicals and reactive nitrogen species free radicals,which has good degradation performance for trace organic pollutants in water,making UV/chloramine system have great application potential in water treatment.In this study,CQP was selected as the target drug to investigate the degradation efficiency of UV/chloramine advanced oxidation system on CQP and the effects of different water quality conditions on its degradation.The mechanism of degradation of CQP by UV/chloramine was elucidated using electron paramagnetic resonance(EPR)and competitive dynamics techniques.By means of quantum chemistry calculation,liquid chromatography mass spectrometry(LCMS/MS),gas chromatography(GC)and ECOSAR software,the degradation products of CQP were identified,the degradation path was speculated,the generation of disinfection by-products(DBPs)was explored,the toxicity level of CQP and its products was evaluated,and the degradation products of CQP by UV/chloramine were described.It was found that chloramine alone and ultraviolet alone could not effectively degrade CQP of the target drug,while UV/chloramine system could efficiently degrade 92.3% of CQP,and the reaction was in accordance with the pseudo-first-order reaction kinetics(R2 > 0.99,k CQP=0.0151 min-1).The concentration of chloramine oxidant,p H(6.0～9.0),HCO3-and NO3-promoted the degradation of CQP in UV/chloramine system to varying degrees,while the presence of Cl-and HA inhibited the degradation of CQP in UV/chloramine system.The types of free radicals in the UV/chloramine system were qualitated by EPR,and the detection map showed that there was an obvious hydroxyl radical characteristic peak.CQP has different reaction characteristics with ·OH and Cl· in the system.Although the steady-state concentration of ·OH in the system is higher than that of Cl·,the combination of CQP and Cl· is more efficient.Therefore,in terms of free radical contribution,the contribution rates of CQP and Cl· are equivalent,respectively 34.7% and 34.2%.A total of 11 products were detected by Liquid chromatography-mass spectrometry/mass spectrometry(LC-MS/MS).Combined with quantum chemistry calculation,the most active reaction site is 11 N.UV/chloramine system mainly realized the degradation of CQP through Ndeethylation,deamination and hydrogen extraction.During the reaction,the contents of trihalomethane(THMs),haloacetic acid(HAAs)and haloacetonitrile(HANs)increased first and then decreased,indicating that the addition of oxidizing agent first produced DBPs,and then partially degraded by oxidizing agent and free radical oxidation.The effects of UV/ chloramine on the cell viability of Chinese hamster ovarian cells(CHO)during CQP degradation changed with the reaction time,and the toxicity of the reaction solution to CHO first increased and then decreased.In addition,the toxicity results predicted by ECOSAR software showed that both acute and chronic toxicity of CQP were "highly toxic".With the degradation of UV/ chloramine,the toxicity of the product was gradually lower than that of the parent compound,but the UV/ chloramine system could not completely mineralize it,so the toxicity level of the intermediate product could not be ignored.In conclusion,UV/chloramine system is more suitable to be placed at the end of water treatment process for further treatment.This study comprehensively evaluated the efficiency,mechanism and toxicity of UV/chloramine system to degrade CQP,in order to provide theoretical and scientific basis for future research and application.