Using Gas Phase Extraction To Rehabilitate Petrochemical Contaminated Soil

Petrochemicals play important roles in our daily life,but they ofent pollute soil,water resources and do harm to ecosystems during manufacture,use and storage.Soil remediation industry has just started with the developing techniques.It is urgent to develop high-efficiency and low-cost techniques to meet the demand for the upcoming soil remediation.At present,soil remediation techniques include bioremediation,chemical remediation and physical remediation.For the petrochemical hydrocarbon contaminated soil,chemical remediation is not very effective to remove the VOCs contaminants whereas bioremediation needs too long time.This thesis deals with the remediation of a petrochemical contaminated soil in Tianjin.We determined the types and distribution of pollutants,hydrogeological parameters and conventional physical parameters of the soil with the soil data and hydrogeological analysis.The main pollutants are benzene and 1,2,3 trichloropropane.We developed the gas phase extraction techniques to remove them.The main contents of the thesis are as follows1)Investigation on the hydrogeology and history of the site and analysis of the polluted soil and groundwater.The soil had water content as high as 25% with natural density of 2g/cm3 and porosity of 0.4.The organic compounds accounted for 3.1% in the soil.Benzene and 1,2,3-trichloropropane were the main pollutants,and the benzene in deep soil was 1-26 in excess of the standards.2)Vapor extraction of the polluted soil.In terms of the hydrogeological conditions and VOCs pollutants,a pilot test was carried out to obtain the technical parameters.The vacuum degree of the monitored well first increased,then leveled off,and then gradually droped with the extraction time if the extraction well kept a constant vacuum.Setting up different vacuum degrees for the extraction well,we obtained the optimum vacuum degree(40 k Pa)for the extraction well.The silt layer,silty soil layer and silty clay layer had influence radius of 20,12 and 7 meters,respectively.80% pollutes could be removed in one week of extraction,but the rest was difficult to extract after two weeks,and more powerful extraction was needed.3)In view of the tailing phenomenon of the gas-phase extraction technology,the chemical oxidation coupled gas-phase extraction technology experiment was carried out to form a joint repair through in-situ chemical oxidation combined with multi-phase extraction,and the repair effect of chemical oxidation coupled gas-phase extraction was studied.The results showed that: in the process of chemical oxidation coupled gas-phase extraction,the extraction amount and water recovery speed were related to the thickness of the soil aquifer and the soil permeability coefficient The greater the permeability,the faster the backwater speed.The results of chemical oxidation test of extraction and reinjection show that the concentration of pollutants in the extraction well will increase after extraction,and the concentration of pollutants will decrease after injection.After 10 times of extraction and injection balance,the concentration of pollutants will reduce to the target value of repair to avoid tailing.