Study On The Degradation Mechanism Of Typical Psychoactive Substances By Advanced Oxidation Processes

This study investigated the occurrence of 13 psychoactive substances in a wastewater treatment plant?WWTP?in Beijing,and selected ketamine?KET?with a low removal rate and methamphetamine?METH?with a high concentration as the target contaminants.The degradation of METH and KET was systematically studied by UV/H₂O₂,UV/PS,UV/Fe²⁺-H₂O₂/PS.Meanwhile,high performance liquid chromatography-electrospray ionization mass spectrometry?HPLC-ESI-MS?was used to analyze the degradation products of KET and METH in different oxidation systems,and the possible degradation pathways were proposed.The main conclusions are as follows:?1?The occurrence characteristics of thirteen psychoactive substances in the WWTP in Beijing,together with their ecological risks in the effluent were studied.The results showed that thirteen psychoactive substances were detected in both influent and effluent,with the total mass concentrations of 2395.10 and 63.59 ng/L,respectively.Ephedrine?EPH?accounted for 93.9%and 67.8%of the total mass,followed by codeine?COD?and methamphetamine?METH?.KET removal rate was the lowest?18.9%?and the removal of other psychoactive substances occurred mainly in the secondary biological treatment and tertiary treatment units?ultrafiltration membrane and UV disinfection?.The ecological risks of psychoactive substances in the effluent of WWTP were low,with all RQs?risk quotient?values less than 0.10,however,the long-term mixing effects of residual psychoactive substances on the ecosystem of the receiving river should not be ignored.?2?The influence of H₂O₂ dosage,initial pH and common water background components?HCO₃^-,Cl^-,NO₃^-,HA?on the degradation kinetics of KET and METH by UV/H₂O₂ was investigated.The results showed that UV or H₂O₂ alone had no effect on their removal.UV/H₂O₂ had a strong synergizing effect,which could effectively remove 99%of KET and METH?100?g/L?within 120 and 60 min,respectively.The degradation followed pseudo-first order reaction kinetics well?R²>0.99?.According to the competition kinetics,the rate constants of?OH with KET and METH were calculated to be 4.43×10⁹ and 7.91×10⁹M^-1·s^-1,respectively.The k_obs gradually increased with the increase of H₂O₂ dosage and reached the maximum at pH 7.The degradation of KET and METH were significantly inhibited by HCO₃^-,Cl^-,NO₃^-,HA,among which Cl^-had relatively little effect on the degradation of KET.Seven reaction intermediates of METH in UV/H₂O₂ system were identified by UPLC-MS/MS,and the possible degradation pathways were speculated.?3?The degradation effect and pathway of KET and METH by UV/PS were studied.The results showed that 100?g/L of KET and METH could be completely degraded by UV/PS in30 min at pH 7 with 500 and 200?M of PS,respectively.The degradation process of METH and KET by UV/PS was fitted the pseudo-first order kinetic model?R²>0.99?.The free radical capture experiment showed that SO₄^-?and?OH existed simultaneously in the reaction system.The bimolecular reaction rate constants of SO₄^-?and?OH with KET were 3.76×10⁹ and 4.43×10⁹ M^-1·s^-1,with METH were 3.29×10⁹ and 7.91×10⁹ M^-1·s^-1,respectively.HCO₃^-promoted KET degradation but inhibited METH degradation,and Cl^-has a dual effect on KET degradation.NO₃^-and HA both significantly inhibited the degradation of the target compounds.Six reaction intermediates of KET and METH in UV/PS system were identified by UPLC-MS/MS.The degradation mechanism was analyzed and the possible degradation pathways were speculated.?4?The degradation effect and pathway of METH by UV/Fe²⁺-H₂O₂/PS were studied.The results showed the removal rate of METH by UV/Fe²⁺-H₂O₂/PS was over 97%and the METH degradation followed the pseudo-first order kinetic model?R²>0.99?.k_obs increased with the increasing concentration of H₂O₂/PS.The degradation of METH was promoted with low dosage Fe²⁺,while inhibited with HCO₃^-,NO₃^-,HA,and higher Fe²⁺.Cl^-had double effects on the degradation of METH.Free radical capture experiments showed that the coexisting?OH and?O₂H were the main active species in UV/Fe²⁺-H₂O₂ system.The coexisting?OH and SO₄^-?were the main active species in UV/Fe²⁺-PS system.The reaction intermediates of METH in UV/Fe²⁺-H₂O₂/PS system were identified using UPLC-MS/MS.The degradation mechanisms of hydroxylation,ring opening and electrophilic substitution were revealed.?5?By comparing the degradation effect of KET and METH with a series of advanced oxidation systems,it was found that k_obs in UV-H₂O₂/PS system reached the highest under neutral conditions?pH 7?,while k_obs in UV/Fe²⁺-H₂O₂/PS system reached the highest under acidic conditions?pH 3,5?with a molar ratio of Fe²⁺and H₂O₂/PS.Based on competitive kinetics experiments,it is revealed that the bimolecular reaction rate constants of KET,METH in ionic states with?OH and SO₄^-?are higher than those in molecular states.There were 64 figures,24 tables and 284 references in this dissertation...