Study On The Degradation Mechanisms Of Ciprofloxacin In Water By Ultraviolet Activated Persulfate Oxidation(UV/PS)

Recently,antibiotics are one of the most important drugs for treating infectious diseases,and large amounts of these compounds are released into municipal wastewater due to excessive consumption and disposal of unused antibiotics.Antibiotics have been frequently detected in the surface and groundwater bodies,which may caused environmental problems such as bacterial drug resistance,aroused widespread concern.Conventional water treatment methods are difficult to remove antibiotics,so it is of great significance to develop novel technologies for degrading antibiotic efficiently.In this paper,ciprofloxacin（CIP）,a third-generation quinolone drug,was selected as the target pollutant.Vacuum ultraviolet activated persulfate（VUV/PS）and ultraviolet activated persulfate（UVC/PS）processes were used to degrade CIP in water.The reaction mechanisms were studied systematically,the degradation and mineralization of CIP in UVC/PS and VUV/PS systems were compared,the degradation intermediates were detected,and the possible degradation path of CIP in VUV/PS system was proposed.The main conclusions are as follows:（1）Study on reaction mechanism of UVC/PS and VUV/PS systems:Five systems including of PS,UVC,VUV,UVC/PS and VUV/PS processes were constructed to investigate the formation of^·OH and the decomposition of persulfate anion.The results showed that the production of^·OH in these processes is following:PS<UVC<VUV<UVC/PS<VUV/PS,and the decomposition of persulfate anion followed:PS<UVC/PS<VUV/PS,indicate that VUV/PS process is more conducive to the formation of active radicals.In the free radical quenching experiment,when TBA and Me OH were added to UVC/PS system,the degradation efficiency of CIP were84.78%and 75.25%,respectively.When TBA and Me OH were added to VUV/PS system,the degradation efficiency were 80.32%and 77.78%,respectively.Therefore,there are two main radicals in UVC/PS and VUV/PS processes,SO₄^·-and^·OH,of which SO₄^·-plays a main role.（2）Study on degradation and mineralization of CIP by UVC/PS and VUV/PS systems:The degradation and mineralization of these systems followed the rules:PS<UVC<VUV<UVC/PS<VUV/PS,indicating that UVC/PS and VUV/PS systems can degrade CIP effectively.When PS=3.0 m M,the degradation and mineralization of CIP in UVC/PS and VUV/PS systems meets UVC/PS<VUV/PS,and the mineralization are 43.2%and 64.1%,respectively.The optimized conditions of CIP degradation in UVC/PS and VUV/PS systems were as following:PS=7.0 m M,p H=7.00,[CIP]₀=200mg·L^-1.Under these conditions,CIP can be degraded completely within 15 min.The degradation rate is UVC/PS(3.77×10^-1 min^-1)<VUV/PS(5.23×10^-1 min^-1),and the mineralization rate were 79.2%and 84.0%,respectively,which indicates that VUV/PS is more conducive to the degradation and mineralization of CIP in water.（3）Oxidation process analysis of CIP:During the degradation of CIP in UVC/PS and VUV/PS systems,the formation of inorganic ions and organic acids were detected.Under the condition of PS=3.0 m M and after 180 min of reaction,the inorganic ions NH₄⁺-N,NO₃^--N and F^-in UVC/PS system accumulated to 0.44,0.53 and 4.87 mg·L^-1,respectively,while these inorganic ions in VUV/PS system accumulated to 1.23,1.58and 18.26 mg·L^-1,respectively.The formation of inorganic ions and organic acids accorded with the law of VUV/PS>UVC/PS.When PS=7.0 m M,due to the strong oxidation of UVC/PS and VUV/PS systems,the concentrations of organic acids increased first and then decreased.Five aromatic degradation products of CIP in VUV/PS process were also detected by UPLC-QTOF-MS,and a possible degradation pathway of CIP in VUV/PS system was proposed.