Insight Into The Kinetics And Mechanism Of Refractory Organic Pollutants Degradation In The Electro-permanganate-ozone Process

Recently,with people’s increasing environmental awareness,refractory organic pollutants have gradually aroused the attention of researchers for their extremely low concentration,complex structure,wide variety,and perdurability.Permanganate has been widely used in the actual water treatment for its stable performance and low cost without the generation of disinfection by-products.But permanganate oxidation and permanganate-based oxidation have selective oxidation,which makes it has the limited oxidation performance for refractory organic pollutants degradation,and its degradation process is always influenced by the p H of the reaction solution.To solve the above problems,this study proposed a novel Electro-permanganate-ozone process（E-PM-O₃）and systematically evaluated the synergy between electricity,permanganate,and ozone.Then it studied the degradation performance of the E-PM-O₃process and revealed the reaction mechanism and the degradation pathway of pollutant in this process.Finally,it investigated the potential application ability of this process in actual water treatment.This study could provide some references and guidance for future permanganate-based research.The main research contents and conclusions of this paper are shown as follows:（1）This study evaluated the degradation and mineralization performance for the target contaminants of the E-PM-O₃ process and investigated the impacts of the operation condition.The results showed that there was a good synergy between electricity,permanganate,and ozone,whit SI=2.602.The E-PM-O₃ process had a synergetic effect for DCF removal,degrading 89.7%DCF in 20 min.And its reaction rate(6.177 s^-1)was significantly higher than the other six comparison process.Besides,this process also had an outstanding mineralization efficiency with the lowest energy consumption.The investigation of the effect of operation factors proved that improving the addition of oxidants dosage and electric current density could promote the removal efficiency of this process.But when they reached a certain level,further improving these factors had a little positive effect on this process.So,when choosing the operation parameters,we should consider the objective removal efficiency and operating cost.The acidic condition is optimized for the removal of DCF in the E-PM-O₃ process.And the change of p H in the reaction solution is slight,so,the effect of the change of solution p H on the process could be neglected.（2）Mechanism experiments proved that the E-PM-O₃ process could simultaneously promote the generation of·OH and RMn S.Different from our previous studies of the electro-permanganate process,the E-PM-O₃ process could not only generate Mn（Ⅲ）_aqbut also generate Mn（Ⅵ）_aq and Mn（Ⅴ）_aq.Further studies proposed the generation pathways of·OH and RMn S.It could be seen that·OH mainly generated by electro-reduction,homogeneous catalysis effect of Mn²⁺,and heterogeneous catalysis effect of Mn O₂.As for the formation of RMn S,there were mainly two ways,the electro-reduction of high valence manganese and the oxidation of low valence manganese by·OH or O₃.And in the E-PM-O₃ process,electro-direct oxidation,O₃ directly oxidation,·OH oxidation,and RMn S oxidation all made contribution to the removal of DCF,and the relative contribution of they were 4.16%,12.68%,40.54%,and 42.64%,respectively.14types of intermediate products were detected in the E-PM-O₃ process,and we speculated that there were four possible degradation pathways for DCF degradation.And the DCF could be degraded into the smaller molecular matters or inorganic matters by dehydrogenation,decarboxylation,dichlorination,and hydroxylation.（3）Finally,we evaluated the potential application of the E-PM-O₃ process.Compared with the ultrapure water,the E-PM-O₃ process had lower removal efficiency in the actual water matrices.But it could still keep a desirable removal efficiency.Phosphate and bicarbonate could inhibit the degradation efficiency of the E-PM-O₃ process.While chloride ion and humic acid could promote it.The E-PM-O₃ process is also proving to be effective for the degradation of various refractory organics,like carbamazepine,sulfadimethoxine and phenol,except for nitrobenzene and atrazine,which was limited by the generation of·OH.All these results proved that the E-PM-O₃ process could maintain a desirable removal performance in actual matrices,and it also effective for various organics degradation,which shows that it has the potential application for water treatment.In conclusion,this study proposed a novel process,the E-PM-O₃ process for refractory organics degradation with high efficiency.And revealing the reaction mechanism of this process,proposing the generation pathways of reactive oxidation species.It could provide some theoretical basis and reference for future research on electricity catalyzing permanganate.