A Laboratory Scale Research For Removing Gasoline Pollution From Soil Using Soil Vapor Extraction Technology

Soil Vapor Extraction (SVE) is a widely applied technology for removal of volatile organic compounds (VOCs) from unsaturated soil. The experiment was investigated in the laboratory using volatile gasoline as a model contaminant, performed in one dimension porous media column filled with permeable, homogeneous sands. To find the soil clean up time and optimal contaminant removal rate, consider parameters such as the way of air filling in or venting through the column, the flowing air rate, the concentration of the contaminant, the time of the soil vapor extraction process and the aqueous status of the soil.It is shown that in the experiment SVE is a effective remediation technique for cleaning up soils contaminated by gasoline. When the gasoline mass concentration of the sand was 6%, it would take 101 days to remove 42 percent of the contaminant under the spontaneous air flow condition. The numeral half-life of the contaminant was 139 days. Venting air from top by a vacuum pump was better than a air charge pump at bottom, it may more effective if use both. The higher gasoline concentration of the soil, the more time it took venting to remove the contaminant and the more quantity of gasoline stay in the soil. It took 15h to reach 64.5% removal ratio of 1% contaminant concentration soil. If the gasoline concentration reached 7.6%, 62.1% of the contaminant would extract in 5 days. Continuous air flow was much effective than intermittent air flow in total removal ratio, but intermittent air flow was cost-effective. The column vent intermit 18h every day was economical and have an ideal removal, It took 9d to remove 52% of the contaminant. Relatively, the air speed affected the overall gasoline removal ratio most. When the air speed was 800mL/min, it only took 5h to remove half of the contaminant, and 95% of the gasoline removal ratio needed 1.6d. After the efficient contaminant removal period in high air speed, the gasoline concentration of the sand decreased slowly. It was the time to speed down the air to save energy. The contaminant removal ratio reached 99% both the 17% and 10% water content of the soil, relatively the 17% water content of the soil have a better contaminant removal value. However, the high content of the water in soil transferred downwards to the bottom of the column easily, it may contaminate ground water in real conditions. So it was better to reduce the water content of the soil to prevent contaminant infiltration or use SVE technology immediately. In SVE process, the C4-C6 component of the gasoline range organics volatile and diffuse to the air phase quickly, the heavier compound transferred slower to the air, and most of the organic compound stay in the soil at last was C11-C12 component of the gasoline range organics.