Degradation Of Organic Matter Polluted Soil By Sprinkle Mode Dielectric Barrier Discharge Plasma

The soil environment of our country is not optimistic on the whole,the soil pollution in some areas is heavy,the soil environment quality of cultivated land is worrying,and the soil environment problems in the abandoned land of industry and mining are prominent.In the process of remediation of contaminated soil,non-thermal plasma technology has attracted wide attention in recent years.Researchers have carried out a lot of research work and achieved good remediation effect,but there is still a certain distance from its practical application,among which a very important limitation is the problem of mass transfer of active substances in soil.In order to solve the above problems,this paper designed and manufactured a dielectric barrier discharge（DBD）reactor by soil sprinkle mode for the remediation of organic contaminated soil.The traditional degradation mode of gas discharge-active particles entering soil layer with carrier gas-active particles colliding with pollutant molecules was changed into a degradation mode of soil particle gap and particle surface discharge-active particles colliding with pollutant molecules.The remediation effect,mechanism and influencing factors of soil sprinkle into DBD plasma mode for treating atrazine and p-nitrophenol single contaminated soil and its compound contaminated soil were investigated.The main research results are as follows:（1）The effects of electrical parameters,soil parameters and gas parameters on discharge characteristics of the soil sprinkle into DBD plasma reactor were investigated.The operating parameters of the plasma reactor were obtained,that is,the peak-peak value is34-38 k V,the power frequency is 100-400 Hz,the soil entry speed is 0-36 kg/h,the particle diameter mesh is greater than 20 mesh,and the carrier gas type is nitrogen,air and oxygen.（2）Atrazine（ATZ）was selected as the target pollutant to study the degradation effect,influencing factors and degradation mechanism of ATZ under the soil sprinkle into DBD plasma mode.The results show that the soil sprinkle into DBD plasma mode has a good remediation effect on atrazine contaminated soil.After the initial ATZ concentration of 10mg/kg was discharged for 50 s,the degradation efficiency reached 70.95%,the energy efficiency was 0.014 mg/k J,the reaction rate constant was 1.098 min^-1,and G₅₀was 195.8J/g_soil.The degradation efficiency of atrazine increased with the increase of applied voltage and supply frequency.And the degradation efficiency decreased with increasing the initial concentration of pollutants,decreasing the soil particle diameter or decreasing the soil p H.With the increase of soil water content,the degradation of atrazine increased firstly and then decreased,and the optimal value was reached at 0.8%.The results of FT-IR and LC-MS showed that the intermediate products of atrazine contaminated soil were mainly triazine rings after the soil sprinkle into DBD plasma mode treatment,and no oligomers were generated,which was easier to be further degraded.（3）The degradation effect,influencing factors,degradation mechanism of p-nitrophenol（PNP）contaminated soil treated by the soil sprinkle into DBD plasma mode were studied.The results showed that the degradation efficiency of 100 mg/kg PNP contaminated soil was 54.19%,the energy efficiency was 0.109 mg/k J and G₅₀was 337.4J/g_soilafter 50 s remediation.With the increase of applied voltage and treatment time,the degradation efficiency of PNP increased.PNP degradation efficiency increased firstly and then decreased with the decrease of soil particle diameter and the increase of carrier gas flow rate.The degradation efficiency of PNP decreased with the increase of the initial concentration of pollutants and the increase of soil entry speeds.GC-MS and LC-MS showed that most of the degradation products were the initial products of PNP degradation.Toxicity Estimation Software Tool（T.E.S.T.）was used to predict the toxicity of the main intermediate products,which indicated that the toxicity of PNP contaminated soil was significantly reduced after remediation.By changing the degradation efficiency of PNP measured by carrier gas（air,nitrogen and oxygen）,it was found that O·、OH·and O₃played a major role in the degradation process of PNP,while N²⁺and NO_xcontributed little to the degradation process because of their relatively weak oxidation capacity.（4）The remediation effect of the soil sprinkle into DBD plasma mode on ATZ and PNP mixtures contaminated soil was studied,and the mutual effects between pollutants in the remediation process was preliminarily explored.The results showed that compared with the single contaminated soil,the degradation efficiency of ATZ decreased and the degradation efficiency of PNP increased in the mixtures contaminated soil with the same total contamination concentration,which indicated that PNP had more advantages in the competition of active substances.A similar conclusion can be reached by comparing total pollutant removal with total energy efficiency.PNP has a significant effect on the change of the total energy efficiency of the mixtures pollution,while the change of ATZ concentration has no effect on the total energy efficiency.