Study On The Degradation Mechanism Of Enofloxacin From Water With UV Based Oxidation Technology

With the continuous improvement of living standards,ecological and environmental issues have gradually attracted people’s attention.In particular,the massive discharge of antibiotics has potential harm to organisms and humans.Fluoroquinolone(FQs),fourth generation of broad-spectrum antibiotics,was widely used in production and human life.The characteristic of persistence leaded to the capability of biological metabolic was limited.Thus,a large number of the antibiotics was discharged through excrement and urine.Convential process,such as flocculation precipitation,filtration,adsorption,had limited capability for the FQs degradation,thus,this artical in-depth study the gradation of FQs.The emerging advanced oxidation processes(UV、UV/Cl2、UV/ peracetic acid)based on UV light were used to degrade the typical pesticide enrofloxacin in water.The degradation performance and mechanism of UV based advanced oxidation processes on pollutants were described in terms of influencing factors,degradation kinetics,degradation pathways,toxicity evaluation and disinfection by-products.The UV irradiation have been reported as an efficient method for FQs degradation.This study investigated the influence of chemical speciation on enrofloxacin(ENR)photolysis process by UV irradiation.The results showed that chemical speciation of ENR significantly affected the photodegradation kinetics,and the highest degradation rate was observed in the zwitterion form.Presence of natural organic matter(NOM)and inorganic anions had different degrees of influences on ENR photodegradation for three chemical speciation of ENR.The contribution of 1O2 on ENR degradation in neutral and alkalinity condition significantly was higher than that in acidic condition.Compared with chlorination of ENR alone,the yield of trichloromethane(TCM)at acidic condition and neutral condition with UV irradiation was respectively 4.06 and 3.14 folds lower than that without UV irradiation.The haloacetonitrile(HANs)yield at acidic condition with UV pretreatment was higher than without UV pretreatment,whereas otherwise results was founded at neutral and alkalinity condition.Being different from TCM and HANs formation,we founded that acidic condition with UV pretreatment contributed to the decreasing of halonitromethane(HNMs)yield and neutral and alkalinity condition had opposite impacts.Potential toxic risk analysis showed the toxicity obviously decreased in zwitterion form,while toxicity increased in cationic and anionic form after UV irradiation.The synergistic process of UV irradiation and chlorination for the degradation of fluoroquinolone antibiotics was investigated.Degradation efficiency of UV irradiation and chlorine oxidation was significantly lower than UV/chlorine process.The degradation of enrofloxacin in the process well fitted pseudo first-order kinetics.Indirect identify experiment indicate ·OH and Cl· was dominate at degradation of ENR.The contribution of ·OH and Cl· could be calculated and the contribution was 39.3% and 9.4%,respectively.The second-rate constant of Cl· and ·OH with ENR was 3.58× 1011 M-1 s-1and 1.78 × 1010 M-1 s-1,respectively.The increasing of chlorine dosage was accompanied by the increasing of the first reaction rate.p H also significantly affects the degradation rate and acids condition was preceding than alkaline condition.The presence of NOM,nitrate,bicarbonate could significantly affect the degradation rate under UV/chorine process.However,increasing of chloride concentration which not leading the variable of the degradation rate.Intermediate of RNR degradation by UV/chlorine was deteced and propose a degradation pathway.Specially,the ecotoxicity of the enrofloxacin and intermediate was analysis by Chlorella Vulgaris.The result of the ecotoxicity found intermediate of the degradation time was 15 min was the biggest toxicity.However,the products after the degradation time 30 min did not damage the cells.UV/ peracetic acid emerging advance oxidation has attracted many people’s attention.The degradation of enrofloxacin by UV/peracetic acid process conforms to the pseudo-first-order reaction rate model.The degradation rate of enrofloxacin in UV/peracetic acid process was 3.09 and 2.93 times higher than that in UV alone and peracetic acid alone,respectively.When the concentration of oxidant increases from 20 to120 mg/L,there is a positive correlation between the concentration of oxidant and the degradation rate.When the concentration further increases,the reaction rate begins to decline.The degradation rate begins to increase as p H increases.Bicarbonate and chloride ions had little effect on the degradation of enrofloxacin,while nitrate ions promoted the degradation of enrofloxacin at low concentration,but the inhibition increased with increasing concentration.Compared with alone UV or PAA oxidation,the process of UV/PAA could efficiently inhibite the production of DBPs...