Experimental Study On Soil Vapor Extraction To Remove Volatile Organic Compounds In Soil

As an in situ remediation technology, soil vapor extraction (SVE) has been widely used to remove volatile organic compounds (VOCs) from soil. In order to find the optimum conditions of removing volatile organic compounds (VOCs) from soil by soil vapor extraction (SVE) technology. Through simulated the ventilation process of SVE, some parameters such as the different continuous ventilation, the different soil water content and intermittent aeration,the diameters of soil columns, soil particle size and different types of pollutants have been studied on restoring yellow brown soil contaminated by benzene and two groups of toluene, ethylbenzene, n-Propylbenzene and benzene, toluene, ethylbenzene. The results showed that when the soil contaminants only one kind of benzene, it was get into tailing stage within 10h and the removal efficiency of benzene was more than 99% at 0.03 L·min^-1 ventilation flow rate ;the ventilation flow rate and soil water content were two important factors on SVE, and they both had the best values.When the column diameter was 14cm, the soil particle size of 10 mesh, continuous up-flow rate of 0.15L·min^-1 and water content about 17.98%, the removal efficiency of toluene, ethylbenzene, n-Propylbenzene and TVOCs amounts to 99.84%,99.45%,98.25% and 99.30%, The repairing effect is best and superior to intermittent ventilation. When soil water content is 6.01% 24.73% the removal efficiency of TVOCs only amounts to 63.03% and when soil water content is 24.73% the removal efficiency of TVOCs only amounts to 89.03%. The results showed that water content which is too high or too low is disadvantageous to the removal of VOCs.The other results showed that the larger bottom area /soil height (S/H) , the better efficient when different column diameter and the same weight of soil loading; soil particle size is 20-40 mesh, soil density increased, non-aqueous phase liquids ( NAPLs) and gas phase mass transfer coefficient decreased, SVE efficiency will be reduced; Another group of experiments study on the removal efficiency of benzene, toluene, ethylbenzene in yellow brown soil when the ventilation flow rate are 0.1L·min^-1 and 0.2L·min^-1. The results showed that benzene, toluene, ethylbenzene are get into tailing stage within 12h ,18h and 24h respectively, and the removal efficiency of TVOCs amounts to 99.52% and 99.55%. The pollutants can be removed very well When the ventilation flow rate is 0.1L·min^-1. After compared with the efficiency of ventilation flow of 0.15L·min^-1 and 0.10L·min^-1 knows that the longer branched chain on benzene ring, the higher boiling point, the lower saturated vapor pressure and the less volatile, furthermore, toluene and ethylbenzene are desorbed and hindered significantly by n-Propylbenzene which is lowest saturated vapor pressure and make toluene, ethylbenzene and n-Propylbenzene polluted soil more difficult to purify. Molecular structure and property are the important factors which also affect the pollutants removal efficiency.