| Soil is the basis for the survival of all kinds of organisms in nature,the premise for the harmonious coexistence of man and nature,and an important guarantee for the safety of the ecological environment.Soil safety is directly related to the survival and development of human beings.Total petroleum hydrocarbon（TPH,Total petroleum hydrocarbon）mainly comes from the development and use of crude oil,industrial production activities,oily wastewater discharge and leakage caused by natural factors.TPH contains toxic components,pollutes soil and groundwater,changes soil microbial communities,changes soil structure and physicochemical properties,and makes soil a carrier of harmful substances,which in turn endangers soil ecology,human,animal and plant health.The treatment and restoration of TPH-contaminated soil is urgent.Chemical remediation technology is a direct,high-efficiency,short remediation period,and in-situ remediation technology for TPH-contaminated soil.This technology converts and degrades TPH pollutants in soil by adding chemical oxidizing agents and activators to the contaminated soil.The purpose of eliminating or reducing soil toxicity.In this paper,the purple soil in southwest China is taken as the research object,and the screening value of TPH(C10-C40)for the first type of land in"Soil Environmental Quality Construction Land Soil Pollution Risk Management and Control Standard（Trial）"（GB36600-2018）is 826 mg/kg and The screening value of the second type of land is 4500 mg/kg as the evaluation standard,and the Ca O2 like Fenton,activated Na2S2O8,and Ca O2/Na2S2O8 composite are selected as the oxidation system,and the optimal oxidation conditions of each oxidation system and the oxidation conditions are determined by single factor and orthogonal experiments.The scope of remediation of soil TPH content was investigated;the influence of soil physicochemical properties on the TPH-loading capacity of purple soil and the remediation effect of the three oxidation systems were investigated;The main research results are as follows:1.The single factor and orthogonal design optimization experiments of oxidation conditions show that:under the condition that the TPH content of the test soil is 10015 mg/kg and the reaction temperature is room temperature 25℃,the optimal oxidation conditions of the Ca O2 like Fenton oxidation system are:the dosage of Ca O2 is 1.4 mmol/g soil,the water-soil ratio was 3.5:1,the molar ratio of Ca O2:Fe SO4:CA was 3.5:1:1,the initial p H was 7.0,and the TPH degradation rate was 78.94%after 48 h reaction;the optimal conditions for the activated Na2S2O8 oxidation system were as follows:The dosage of Na2S2O8 was 0.7 mmol/g soil,the water-soil ratio was 2:1,the molar ratio of Na2S2O8:Fe SO4:CA was 15:1:1,the initial p H was4.5,and the TPH degradation rate was 85.27%after 48 h reaction;The Ca O2/Na2S2O8 optimal conditions for the Na2S2O8 composite oxidation system are:the dosage of Na2S2O8 is 0.6mmol/g soil,the water-soil ratio is 3.5:1,the molar ratio of Na2S2O8:Ca O2:Fe SO4:CA is10:10:1:1,the initial p H is 7.5,and the The degradation rate of TPH in 48 h reaction was 92.47%.2.Soil remediation experiments with different TPH contents showed that soil TPH degradation rate was negatively correlated with soil TPH content.The Ca O2 like Fenton oxidation system can remediate the soil with a TPH content below 6000 mg/kg to meet the requirements of the first category of land,and the soil with a content of less than 12000 mg/kg to meet the requirements of the second category of land;the activated Na2S2O8 oxidation system can remediate the TPH content The soil remediation below 6000 mg/kg meets the requirements of the first type of land use,and the soil remediation below 14000 mg/kg meets the second type of land use requirements;the Ca O2/Na2S2O8 composite oxidation system can remediate the soil with a TPH content below 10000 mg/kg.Meet the requirements of the first category of land use,and remediate the soil with a content of less than 15000 mg/kg to meet the second category of land use requirements.3.Under the condition of TPH dosage of 15000 mg/kg,the effects of different organic matter content,particle size and cation exchange capacity on soil TPH loading capacity were investigated.The system carried out oxidation remediation experiments on soils loaded with different TPH contents.The experiments showed that the soil TPH loading capacity was positively correlated with soil organic matter content and cation exchange capacity,and negatively correlated with soil particle size.The degree of influence was:organic matter content>particle size>cation exchange capacity;soil TPH degradation rate is negatively correlated with soil organic matter content,cation exchange capacity and particle size,and the degree of influence is:particle size>organic matter content>cation exchange capacity.4.The small test experiment of chemical oxidation remediation of actual contaminated soil in a TPH-contaminated site in Chongqing shows that the soil type is red loam,the TPH content is 8156 mg/kg,the organic matter content is 4.31%,and the p H is 7.64.The actual site TPH-contaminated soil,Ca O2 like Fenton,Activated Na2S2O8,and Ca O2/Na2S2O8 composite oxidation systems reacted under the optimal oxidation conditions for 48 h,and the soil TPH degradation rates could reach 69.46%,76.66%,and 90.22%,respectively.The Ca O2/Na2S2O8composite oxidation system can remediate the actual site polluted soil with a TPH content below 8000 mg/kg to meet the requirements of the first category of land use;the Ca O2 like Fenton oxidation system and the activated Na2S2O8 oxidation system can be used.The remediation of contaminated soil on the site meets the requirements for the second category of land use.A comparative study on the changes of soil p H,organic matter content and cation exchange capacity before and after the restoration of the three oxidation systems.After restoration by the Ca O2 like Fenton and activated Na2S2O8 oxidation systems,the soil p H was9.76 and 2.51,respectively.After restoration,the soil p H needs to be adjusted.The soil p H after restoration by the Ca O2/Na2S2O8 composite oxidation system was 7.85,which belonged to the normal soil p H range.The organic matter content of the three oxidation systems decreased by1.69%-1.97%,and the cation exchange capacity changed little.5.Under the optimal oxidation conditions,the Ca O2/Na2S2O8 composite oxidation system is superior to the Ca O2 like Fenton and activated Na2S2O8 oxidation system in terms of TPH remediation effect and influence on soil properties.It is an efficient and green TPH-contaminated soil treatment and remediation technology. |
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