Study On Removal Efficiency And Mechanism Of Pharmaceutical Contaminants By Electroactivated Peracetic Acid In Water

Pharmaceutical contaminants（PhACs）are a class of emerging contaminants that are widely found in natural water bodies,soil,waste leachate and other environmental media,posing a great threat to drinking water safety,human health and ecological environment.Existing technologies are not only difficult to remove them efficiently,but also have problems such as high energy consumption,secondary pollution and poor practical application.To this end,a novel electro-activated peracetic acid（EC/PAA）system based on peracetic acid（PAA）advanced oxidation technology was proposed in this study,and the removal performance of three systems,sole EC,peroxyacetic acid（PAA）alone,and electro-activated peracetic acid（EC/PAA）,on typical PhACs（carbamazepine,CBZ）was investigated,and the systematic evaluation of the EC and PAA between the synergistic efficiency and mineralization efficacy between EC and PAA were systematically evaluated,and the effects of PAA dosing,current density,p H,and initial CBZ concentration on the removal efficacy of the EC/PAA system were investigated.The experiments of free radical quenching,electrochemistry and electron paramagnetic resonance technology（EPR）were used to identify the active species and intermediate products in the system,reveal the intrinsic reaction mechanism and the possible main degradation pathways of pollutants in the EC/PAA system,and explore the potential applications of the system.The research results could provide a certain theoretical basis for the subsequent research based on PAA advanced oxidation technology.The main findings of the paper are as follows:（1）EC and PAA have good synergistic effect with a synergy coefficient of 2.19.Under the conditions of initial CBZ concentration of 10 mg L^-1,PAA injection of 10mmol L^-1and current density of 20 m A cm^-2,the EC/PAA system has better degradation effect than other systems,and could remove 94.2%of CBZ in 120 min with a reaction rate of up to 0.02308 min^-1and the removal rate of TOC was 64.3%,and the system could achieve efficient degradation of pollutants with low energy consumption.The system was influenced by the initial p H of the solution,because the solution p H is higher than the p Ka of PAA（8.2）,the PAA will undergo autolysis,so the system could have a high removal effect under acidic or neutral conditions.（2）The EC/PAA system could promote the production of reactive substances such as hydroxyl radicals（·OH）,organic radicals（R-O·）,superoxide anions（O₂·^-）and singlet oxygen（¹O₂）.Among them,·OH and R-O·are mainly produced through the direct supply of electrons to PAA by the cathode,leading toα-H fission of PAA;while ¹O₂is produced through the reaction of H₂O₂with·OH in the system.The contribution of·OH in the EC/PAA system was found to be 40.2%and 52.04%by both the probe method and the capture experiment,respectively.The contribution calculated by this method was too high because the capture experiment ignored the consumption effect of excess tert-butanol（TBA）in capturing·OH by PAA.The detection and analysis of CBZ degradation intermediates in the EC/PAA system revealed that CBZ first generated hydroxylation,carboxylation and hydrogen atom extraction products,followed by different intermediate degradation products through dehydrogenation,decarboxylation,polymerization,bond breaking and recombination,which were further oxidized to H₂O,CO₂and other products.（3）The removal of CBZ by the EC/PAA system was 94.2%,84.1%and 74.2%for ultrapure water,tap water and surface water as background water bodies,respectively.This may be due to the fact that the natural organic matter（HA）and some inorganic ions(Cl^-,HCO₃^-,PO₄^3-)contained in the surface water remove·OH and R-O·through competitive reactions,thus weakening the oxidation efficiency of the system.Although the degradation of CBZ in surface water and tap water by the EC/PAA system is not as good as that of ultrapure water,the overall removal of CBZ could be maintained at more than 70%.Among them,the presence of bicarbonate ions（HCO₃^-）,phosphate ions(PO₄^3-),chloride ions（Cl^-）and humic acid（HA）in water inhibited the degradation ability of the EC/PAA system for CBZ.In addition,the EC/PAA system can also be used for the removal of a variety of refractory organic pollutants such as sulfamethoxazole（SMX）,naproxen（NPX）and ciprofloxacin（CIP）,all with good synergistic effects and removal efficacy,indicating that the system has good potential for application.