Study On Activating Persulfate By Gas-Liquid Two-Phase Discharge For Degradation Of Benzene

Volatile organic compounds?VOCs?can cause harm to human health and the ecological environment.The technologies used to treat VOCs include catalytic combustion,photocatalysis,biological methods,and plasma technology.Non-thermal plasma technology has the advantages of wide applicability,rapid start-up and shutdown of the process,high processing efficiency,and low requirements for the pretreatment process;however,the gas-phase discharge plasma also has problems of low degradation rate or some toxic by-products.This paper proposes a liquid film dielectric barrier discharge?DBD?reactor to degrade VOCs to solve the above problems.Using benzene as the simulated target pollutant,the study found that compared with other DBD reactors,the liquid film dielectric barrier gas-liquid two-phase discharge reactor can produce active species in both the gas and liquid phases at the same time,so that gaseous pollutants can react with the active species in the gas phase and the by-products easily soluble in water generated during the reaction can be further oxidized and decomposed into CO₂ and H₂O in the liquid phase,which will improve the degradation efficiency of benzene.In addition,adding persulfate?PS?oxidant to the liquid phase to form a liquid film DBD/PS composite system can further improve the degradation efficiency of benzene.The main research contents and results of this article are as follows:?1?For benzene degradation in the liquid film DBD reactor,When increasing the discharge voltage,power frequency,and reducing the gas flow rate and the concentration of benzene,the degradation rate of benzene can be improved.As the voltage and frequency and the concentration of benzene increase,the energy efficiency of benzene decreases,and as the residence time increases,it will rise first and then will reduce.The circulation flow rate of the solution has little effect on the degradation of benzene.Strong acid or base pH value of the solution will reduce the degradation rate of benzene;as the conductivity increases,the degradation rate of benzene increases first and then decreases.The change law of energy efficiency is the same to the degradation rate of benzene.?2?For the production of active species in the liquid film DBD reactor,t the concentrations of H₂O₂,O₃ and nitrate ions increase with the peak pulse voltage,power frequency,and water circulation flow rate.Air flow rate has different effects on the production of active species.When the air flow rate is 0.4 mL/min,the concentration of active species produced is higher.In addition,an increase in pH and conductivity results in a decrease in H₂O₂ and O₃ concentrations,while nitrate ions increase with the pH and conductivity of water.?3?For benzene degradation in the liquid film DBD/PS system,its degradation rate is higher than that of the liquid film DBD system.The higher the applied voltage and frequency are,the more the degradation efficiency increases.When the concentration of persulfate increases,the degradation rate of benzene increases first and then remains basically unchanged.A decrease in the gas flow rate and benzene concentration can increase the degradation rate of benzene.The circulating flow of the solution will increase the degradation rate of benzene,and acidic or basic conditions have a negative effect on the degradation of benzene.?4?Compared with the liquid film DBD system,the liquid film DBD/PS system significantly increased the ozone concentration,but decreased the hydrogen peroxide concentration.EPR spectroscopy was used to identify the free radicals generated by the DBD/PS system,and it proved that the liquid film DBD/PS system can produce SO₄^-·and·OH.Ethanol and tert-butanol are used as free radical scavengers,and the results show that both SO₄^-·and·OH are involved in the DBD/PS oxidation process.NaN₃ is an effective scavenger for removing¹O₂,and the result indicates that ¹O₂ can promote the degradation of benzene or also participate in the degradation of benzene.NO₃^-is e_aqq scavenger,and an addition of NO₃^-into the solution has an inhibitory effect on benzene degradation,indicating that e_aqq has a certain role in benzene degradation,and e_aqq also plays a role in PS activation.