Study On Removal Of Diclofenac In Water By Peracetic Acid And Peroxymonosulfate-based Advanced Oxidation Processes

Pharmaceuticals and personal care products（PPCPs）,as emerging contaminants in water environment,may produce a potential threat to aquatic life and human health.Diclofenac（DCF）is a commonly used non-steroidal anti-inflammatory drugs（NSAIDs）for the treatment of arthritis,pain and fever.Due to widespread application and low removal efficiency in traditional sewage treatment processes,it has become one of PPCPs with high detection frequency in surface water and ground water with the concentration ranging from ng L^-1 toμg L^-1.DCF can produce acute or chronic toxicity and bioaccumulation effects on shellfish,fish,amphibians and even birds,thus threatening human health.Therefore,it is necessary to explore some effective new methods to remove DCF from contaminated water.In this paper,DCF was selected as the target pollutant,and four advanced oxidation processes（AOPs）,i.e.,ultraviolet（UV）activated peracetic acid（PAA）（UV/PAA）,Cu²⁺enhanced UV activated PAA(Cu²⁺/UV/PAA),zero valent copper（ZVC）activated PAA（ZVC/PAA）and ZVC activated peroxymonosulfate（PMS）（ZVC/PMS）,were explored to degrade DCF in water.The main contents as followed:（1）The degradation kinetics and mechanism of DCF by UV/PAA were investigated.The reactive radicals produced in UV/PAA system were identified by radical scavenging experiment.The effects of different factors on DCF removal were discussed,the removal of TOC in the system was analyzed,and the degradation products of DCF were detected.It was found that the addition of PAA could enhance DCF degradation in UV system,which was due to the role of HO^·,CH₃COO^·and CH₃COOO^·produced by the photolysis of PAA.The degradation of DCF in UV/PAA system followed the pseudo first-order kinetics.In the p H range of 3.0-11.0,DCF had the highest observed pseudo first-oder reaction rate constant(k_obs)at p H 8.5,and its k_obs was enhanced with the increase of PAA dose.Cl^-,SO₄^2-and Fe³⁺had almost no effect on DCF degradation,CO₃^2-,NO₃^-and Cu²⁺improved the degradation of DCF,while dissolved organic matter（DOM）inhibited DCF removal.Moreover,the degradation of DCF in actual water was inhibited.The mineralization rate of DCF by UV/PAA was low,and the elimination of total organic carbon（TOC）within 50 min was at only 8.6%.Prabable degradation pathways of DCF in UV/PAA system included hydroxylation,decarboxylation,formylation,dehydrogenation,dechlorination-hydrogenation,dechlorination-cyclization,dechlorination-hydroxylation and amidation.（2）The degradation kinetics and mechanism of DCF by Cu²⁺/UV/PAA were investigated.The reactive radicals produced in Cu²⁺/UV/PAA system were identified by radical scavenging experiment.The effects of different factors on DCF removal were discussed,the removal of TOC in the system was analyzed,and the degradation products of DCF were detected.It was found that both UV and Cu²⁺could activate PAA to produce HO^·、CH₃COO^·and CH₃COO^·,which could promote DCF removal.The degradation of DCF by Cu²⁺/UV/PAA followed the pseudo first-order kinetics and its degradation was probably attributed to direct photolysis,HO^·oxidation and organic radicals（RO^·）oxidation such as CH₃COO^·and CH₃COOO^·.In the p H range of 3.0-11.0,DCF had the highest k_obs at p H 8.5,and its k_obs was enhanced with the increase of PAA dose and Cu²⁺dose.NO₃^-promoted the degradation of DCF,while Cl^-,SO₄^2-,CO₃^2-and DOM had little effect on DCF removal.Compared with UV/PAA,the degradation of DCF in actual water by Cu²⁺/UV/PAA almost was not inhibited,and the mineralization rate of DCF was slightly higher（the elimination of TOC within 50 min was at 11.3%）.The transformation path of DCF in Cu²⁺/UV/PAA was similar to that in UV/PAA system.（3）The degradation kinetics and mechanism of DCF by ZVC/PAA were investigated.Based on the X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）and field emission scanning electron microscope（FESEM）characterization results of ZVC before and after reaction and radical scavenging experiment,the degradation mechanism of DCF by ZVC/PAA was proposed.The effects of different factors on DCF removal were discussed,the removal of TOC in the system and the reusability of ZVC were analyzed,and the degradation products of DCF were detected.It was found that PAA could be activated by ZVC to produce HO^·,CH₃COO^·and CH₃COOO^·,which were responsible for the removal of DCF.The corrosion of ZVC was occurred to produce Cu⁺under acidic condition,which was the main activator for PAA,H₂O₂ and O₂.The degradation of DCF in ZVC/PAA system followed the pseudo first-order kinetics.The recommended p H for this reaction system was3.0,and the k_obs of DCF was enhanced with increasing ZVC dose and PAA dose.Cl^-,CO₃^2-,Fe³⁺,Cu²⁺and DOM promoted DCF degradation,while SO₄^2-and NO₃^-had almost no influence on DCF removal.In addition,the degradation of DCF in actual water was slightly inhibited.The mineralization rate of DCF by UV/PAA was low,and the elimination of TOC within 60 min was at only 6.9%.After three times of recycling,ZVC still maintained high catalytic activity.The probable degradation pathways of DCF in ZVC/PAA system included hydroxylation,amidation,dechlorination-cyclizaiton,dechlorination-hydrogenation,dechlorination-hydroxylation,decarboxylation and formylation.（4）The degradation kinetics and mechanism of DCF by ZVC/PMS were investigated.According to the XPS,XRD and FESEM characterization results of ZVC before and after reaction and radical scavenging experiment,the activation mechanism of PMS by ZVC was proposed.The effects of different factors on DCF removal were discussed,the removal of TOC in the system and the reusability of ZVC were analyzed,and the degradation products of DCF were detected.It was found that PMS could be activated by ZVC to produce SO₄^·-and HO^·,which were responsible for DCF removal.The corrosion of ZVC was occurred to produce Cu⁺under acidic condition,which was the main activator for PMS.The degradation of DCF in ZVC/PMS system followed the pseudo first-order kinetics.In the p H range of3.0-11.0,DCF had the highest k_obs at p H 3.0,and its k_obs was enhanced with increasing ZVC dose and PMS dose.NO₃^-and Cu²⁺had almost no influence on DCF removal,Cl^-,Fe³⁺and DOM promoted DCF degradation,while HCO₃^-and high concentration of SO₄^2-inhibited DCF removal.Moreover,the degradation of DCF in actual water was inhibited.Druing the removal of DCF by ZVC/PMS,the elimination of TOC within 30 min was 22.8%.After three times of recycling,ZVC still maintained high catalytic activity.The probable degradation pathways of DCF in ZVC/PMS system included hydroxylation,dehydrogenation,decarboxylation formylation and dechlorination-cyclizaiton.To sum up,UV/PAA,Cu²⁺/UV/PAA,ZVC/PAA and ZVC/PMS systems all could effectively remove DCF in water,but Cu²⁺/UV/PAA and ZVC/PAA systems were more suitable for the removal of DCF in actual water.