Investigation Of Mechanism In Oxidizing Species And Aqueous Pollutants Decomposition Induced By Pulsed Corona Discharge Treatment

Advanced oxidation processes?AOPs?based on ozone exhibit high energy efficiency in the treatment of wastewater with refractory organic pollutants.Pulsed corona discharge?PCD?as a kind of AOPs with highest energy efficiency,the advantage in water treatment with electric discharge is the production and utilization of oxidative species in situ,namely ozone and hydroxyl radicals?·OH?,thus avoiding the energy loss from the synthesis of ozone.Application of PCD to the gas-liquid mixtures increases the oxidation efficiency of aqueous pollutants for a few times using short-living reactive oxygen species generated in gas-liquid surface and airborne long-living reactive oxygen species through mass transfer between gas-liquid phase,together with physical field.In this research,the combination of the oxidation mechanism of oxidative species and pollutants decomposition based on PCD oxidation as the main content provides the theoretical and technical support for the application of PCD in water treatment.In this study,scavengers of·OH were applied to the degradation of three kinds of target pollutants with different kinetics to explore the role and distribution of the short-living and long-living oxidative species in the oxidation of organic compounds.Thiocyanide was used as the target pollutant.The pollutant conversion pathway and influencing factor based on the oxidation by PCD were investigated.The choice of energy input rate in treatment of aqueous media with PCD requires quantification of reactive oxygen species reactions dependent on oxidation kinetics,i.e.,the condition of reactor could be chosen to oxidize different organic pollutants for the high energy efficiency.The role of surfactant and non-surfactant·OH scavengers in PCD was studied in respect of oxidation of phenol,oxalic acid and humic acid,and the performance of target pollutants degradation under different pulse repetition frequency was also investigated.The target pollutants have different degradation kinetics.Phenol reacts fast,whereas oxalate is known to selectively react with OH-radicals.Humic acid oxidation is slow.Results disclosed the mechanism of phenol oxidation with surface-borne radicals and long-living ozone oxidizing also via radical mechanism in the bulk of treated solution.Oxidation of oxalate takes place predominantly with the surface-borne radicals since the non-surfactant scavengers ruling out radicals formed in the bulk reactions reduce the oxidation efficiency to a two-fold smaller extent.Oxidation of HA is insensitive to oxidants,and its oxidation depends only on the·OH from the interface due to the scavenger impact by itself.Results showed that rapid energy intake is advised for oxidation induced exclusively by radical reactions,such as humics,whereas abatement of admixtures reacting with both surface-borne and long-living oxidants benefits from reduced pulse repetition frequency.Overall,the predominant role of surface-borne reactions was confirmed in PCD treatment of aqueous media.Aiming at constructing appropriate conditions for the anammox process,simulated thiocyanate wastewater was taken as the research object.The dynamic transformation of nitrogen pollutants under different pH conditions was investigated along the PCD treatment.The effects of SCN^--N degradation by-product(SO₄^2-and HCO₃^-)concentrations on the transformation of NH₄⁺-N was studied.And,the degradation kinetics of NH₄⁺-N under different conditions was studied by fitting to 0-order model.Results showed that PCD technology could effectively oxidize nitrogenous compounds including SCN^--N and NH₄⁺-N to NO₃^--N by in-situ generated O₃ and·OH,and the increase in pH is beneficial to the oxidation reaction.SO₄^2-and HCO₃^-produced in the process of SCN^--N oxidation have significant inhibitory effects on the PCD oxidation of NH₄⁺-N.The inhibitory effects of HCO₃^-is higher than SO₄^2-.This work indicates that for the treatment of wastewater with high concentration of SCN^-,PCD technology can be used as a pretreatment technology for the anammox process,which exhibited superiority in terms of eliminating toxicity inhibition and creating suitable water quality characteristics.In light of above work,due to the rapid conversion of thiocyanide to ammonia based on PCD,PCD can be used as a pretreatment process of anammox for the removal of total nitrogen by adjusting the reaction conditions.Combined with the different role of the scavengers,the effect and distribution of oxidants in the oxidation of pollutants with different kinetics were summarized.This work dealt with establishing detailed regularities in water treatment by PCD,and the interface reaction was verified.These obtained results could potentially provide theoretical support for the industrial application of PCD technology.