| Shale gas is a clean energy source that can greatly meet energy demand,but at the same time,shale gas mining cause serious petroleum hydrocarbon pollution to the surrounding soil environment.Conventional chemical oxidation is difficult to degrade refractory components in petroleum hydrocarbons efficiently.However,advanced oxidation processes based on sulfate radical can effectively degrade refractory organic pollutants,which has broad application prospects in the field of soil remediation.In this paper,the situation of petroleum hydrocarbon pollution in the shale gas development site was investigated and the status of soil petroleum hydrocarbon pollution in a typical shale gas development site has been identified.Taking petroleum hydrocarbons as the research object,using ultrasonic,heat,zero-valent iron alone activated sodium persulfate and ultrasonic/thermal,ultrasonic/zero-valent iron composite activated sodium persulfate as the research methods,the effects of different activation methods on the degradation of petroleum hydrocarbons in soil were investigated through laboratory test,and the related influencing factors in the degradation process were explored.The kinetics of oxidative degradation process was revealed and the petroleum hydrocarbon degradation process was analyzed.The main results are as follows:(1)The soil sample analysis results of the typical shale gas development site indicated that the petroleum hydrocarbon pollution in the development site was mainly concentrated at 0-20 cm in the soil surface.The petroleum hydrocarbon pollution in the mud storage area was the most serious,and the petroleum hydrocarbon concentration could reach 5140 mg/kg.The petroleum hydrocarbons in the regional polluted soil did not exceed 10,000 mg/kg.(2)The laboratory test of different activation methods for remediation of contaminated soil showed that in the contaminated soil with a hydrocarbon petroleum concentration of 19850 mg/kg,the removal rate of US activation for 3 days was 56.41%,and the removal rates of other methods for activation of 3 d were above 70%.The petroleum hydrocarbon degradation in each repair process was consistent with the first-order reaction kinetics model.The composite activation treatment was obviously better than the single activation.The most effective activation method was US/zero-valent iron composite activation.The petroleum hydrocarbon removal rate was 10%higher than the single iron activation,and the petroleum hydrocarbon removal rate was 82.23%.Rapid and efficient degradation of petroleum hydrocarbons can be achieved.The best composite method US/zero-valent iron activation process pH was close to neutral,which is conducive to the implementation of soil remediation.(3)The analysis of the influencing factors of each repair process showed that the free radical transfer process was mainly based on water and the repair effect can be enhanced by the influence of soil permeability and other factors.The main controlling factors of different activation methods were water-soil ratio,but the amount of water in the soil should be reasonably controlled to avoid excessive sulfate in groundwater;followed by sodium persulfate addition.pH had little effect on the treatment effect.(4)The degradation process of petroleum hydrocarbons in soil showed that the reaction mainly concentrated on 0.5 d before in the oxidative degradation of petroleum hydrocarbons of activated persulfate technology.The first 4 hours was the rapid degradation stage,and the apparent removal rate can reach 30.38 g/h.The cycloalkanes,alcohols,alkanes and olefins experienced substitution and addition reactions to form halogenated hydrocarbons and alkanes.Due to the slow oxidative degradation rate of saturated alkanes above C16,it mainly existed in the form of long linear paraffins mainly composed of C16-C21 in the end.The order of degradation of petroleum hydrocarbon pollutant components was:cycloalkanes,alcohols,esters,olefins,saturated alkanes above C16 and halogenated hydrocarbons. |
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