Study On Degradation Of Benzo Heterocyclic Compounds By Low Temperature Plasma Synergistic Sulfate Radicals Technology

Benzotriazole（BTA）and benzothiazole（BTH）are two typical benzoheterocyclic compounds.They are formed by condensing a heterocyclic ring with a benzene ring which have a stable chemical structure and have been widely used in industry and agriculture in recent years,and has been commonly detected in sewage,surface water,groundwater and tap water.Because these compounds have high solubility in water,bio-refractory and have certain biological toxicity,entering the water body will cause great damage to the ecological environment.In addition,traditional wastewater treatment technologies could not effectively degrade these compounds.Therefore,in order to ensure the safety of drinking water and water environment,it is necessary to develop a water treatment process which could efficiently,rapidly and green degrade benzoheterocyclic compound wastewater.Dielectric barrier discharge（DBD）plasma technology is a new advanced oxidation process that integrates various physical and chemical effects such as ozone oxidation,free radical oxidation,ultraviolet photolysis and high-energy electron radiation,which has the advantages of high efficiency,quick and easy operation in the process of degrading pollutants.This article takes BTA and BTH as the target organic pollutants,combination DBD plasma and sulfate radical technology to degrade benzoheterocyclic compounds simulate wastewater.Research on the feasibility,influencing factors,and synergistic reaction mechanism of plasma cooperative system.At first,the degradation of benzoheterocyclic compounds in DBD plasma was investigated.It was found that BTA and BTH could achieve 49.0%and 55.2%removal efficiency after 20 min plasma treatment,respectively.The lower the p H was,the greater the BTA degradation efficiency was.On the contrary,the higher the solution conductivity and the discharge voltage was,the better the BTA degradation efficiency was.However,when the conductivity of the solution was greater than 930μs/cm,the degradation efficiency of pollutants was no longer affected by the solution conductivity.A preliminary study of the degradation mechanism of DBD plasma found that the concentration of O₃ and H₂O₂ in the solution could increase with the the discharge time,and the·OH which produced by the plasma discharge makes an important contribution to the degradation of contaminants.Secondly,the feasibility of synergistic degradation benzoheterocyclic compounds by persulfate（PMS）/sulfite with DBD plasma was studied,and the influencing factors and reaction mechanism of synergistic system were discussed.It was found that the solution p H,the amount of PMS/Na₂SO₃ dosage,and the discharge voltage had a significant effect on the degradation effect of the synergistic system;compared with DBD plasma alone,the introduction of PMS and Na₂SO₃ could increase the degradation efficiency of pollutants by 48.0%and 24.9%,respectively.Correspondingly,the energy yield of the plasma system is increased by 84.0%and 36.3%,respectively.The synergy effect was attributed to the activation of PMS and Na₂SO₃ in the DBD plasma,and the mechanism studies show that the addition of PMS and Na₂SO₃ were not only introduces SO₄·^-into the plasma system,but also significantly increased the production of O₃,H₂O₂ and HSO₅^-.According to the experimental results,except of·OH and SO₄·^-,electrons（e^-）,superoxide anion radicals(·O^2-)and singlet oxygen（¹O₂）were also played an important role in synergistic system.In addition,LC-MS was used to analyze the degradation products of BTA,and it was found that the formation of intermediates is mainly through the opening of benzene ring and triazole ring pathway.The toxicity evaluation results of the products showed that the 20 minute DBD-PMS process could effectively reduce the oral rat LD₅₀ and the developmental toxicity of BTA.Finally,the effects of different concentrations of chloride,carbonate and humic acid on the degradation of contaminants in the synergistic system were also investigated.Through degradation experiments under actual water quality conditions,it was determined that the background composition of the water had an inhibitory effect on the degradation of pollutants.However,although in the tailwater of the sewage plant with the worst treatment effect,the contaminants degradation rate of the synergistic system was still higher than 40.68%.Combined with the conclusion that the energy yield of the DBD-PMS synergy system is almost doubled,this study verifies the feasibility of the degradation effects of BTA and BTH by the DBD-SO₄·^-synergy technology under actual water quality conditions.In general,this study provides a new scheme for the treatment of benzoheterocyclic compound wastewater,which can efficiently,greenly and rapidly degrade pollutants.It also provides new ideas for the development and application of low temperature plasma synergy technology.