Study On Cathode/Anode Mediated Activation Mechanism Of Persulfate

Electroactivated persulfate technology has been proved to have a good removal effect on various refractory organic pollutants widely existing in natural water,soil,landfill leachate and other environmental media.However,there are still some problems such as high energy consumption,secondary pollution and poor practical application effect,and the specific reaction mechanism of this technology is not clear.To solve the above problems,an electroactivated persulfate system with anode and cathode separation was constructed,and the synergistic effect between electrochemistry and persulfate was systematically evaluated.The removal efficiency of the anode and cathode separation system and the whole system on carbamazepine（CBZ）,a typical refractory organic pollutants,was investigated,and the reaction mechanism and possible degradation path of carbamazepine in the process of the two systems were explored.The effectiveness of two different methods in exploring the mechanism of electroactivated persulfate system was evaluated,which provided theoretical basis and reference value for the subsequent research on advanced oxidation technology based on electroactivated persulfate system and theoretical guidance for its application in the actual water treatment process.The main research contents and conclusions of this paper are as follows:（1）The effects of electric/persulfate（E-PMS）system on the removal efficiency of CBZ under different operating conditions were investigated,the optimal operating conditions were determined,and the removal and mineralization efficiency of CBZ under negative/anode mediated E-PMS system was evaluated.It is found that with the increase of PMS concentration and current density,the removal efficiency of CBZ also increases.However,when the dosage and current density of PMS increase to a certain value,the further increase will not significantly improve the removal efficiency of the system.In addition,with the increase of initial p H value of solution,the removal rate of CBZ decreased,indicating that acidic conditions were more conducive to the removal of refractory organic pollutants in the system.CBZ removal experiment results show that there is a good synergistic effect between electrochemistry and persulfate,and the synergistic coefficient is 8.568.The E-PMS system has better CBZ removal effect than other control systems,which can achieve 99.15%CBZ removal within 60 min,and the chemical reaction rate reaches 9.056×10^-2min^-1,and the comparison of energy consumption shows that E-PMS system has the lowest energy consumption compared with other control systems.The cathode/anode separation experiments showed that the removal of CBZ by electroactivated PMS with single anode was more effective than that by single cathode electroactivated PMS.（2）The types and production pathways of active substances in E-PMS system were investigated,and the main mechanism of the system on the degradation of CBZ was revealed.·OH,SO₄^·-,O₂^·-,and ¹O₂ were identified using quenchers methanol,tert-butanol,p-benzoquinone and furfuryl alcohol.Further investigation of the production pathway of active substances in E-PMS system showed that·OH,SO₄^·-,O₂^·-,and ¹O₂were produced at the cathode,while·OH,O₂^·-,and ¹O₂ were produced at the anode.The estimated relative contribution rates showed that the relative contribution rates of direct electron transfer reaction（DET）,PMS oxidation alone,non-free radical oxidation and ROS oxidation to the degradation of CBZ were 3.09%,2.65%,0.44%and 93.82%,respectively.By detecting and analyzing the intermediates produced by CBZ in E-PMS,E（cathode）-PMS and E（anode）-PMS systems,it is found that there are 5 cathode degradation paths for CBZ in E-PMS systems.It can be degraded into small molecules of organic matter through dehydrogenation,hydroxylation,C-N bond breaking and ring opening,and finally converted into inorganic substances such as H₂O and CO₂.（3）The effectiveness of quenching method and probe method in E-PMS system was evaluated.It was found that the addition of high concentration reactive oxygen quenchers（such as TBA and p BQ at m M level）had significant effects on the decomposition mechanism of PMS and the generation of reactive oxygen species.Because the reaction mechanism of the system changes significantly in the presence and absence of high concentration reactive oxygen species quencher,the traditional quenching method can not well reveal the real effect of reactive oxygen species on pollutant degradation in persulfate process water treatment.In contrast,the exposure amounts of·OH,SO₄^·-,O₂^·-,and ¹O₂during PMS oxidation and electrocatalytic PMS oxidation were measured using microros probes atμM level,such as p-chlorobenzoic acid（p CBA）,atrazine（ATZ）,carbon tetrachloride（CCl₄）and metronidazole（MDE）,but the reaction mechanism did not change significantly.In addition,the relative contribution of various ROS to pollutant removal can be quantitatively evaluated.These results suggest that the probe method may provide a more realistic way to assess the role of ROS in pollutant degradation in persulfate process water treatment than traditional quenching methods.