Experimental Study Of Soil Venting On The Remediation Of Soil Contaminated By Gasoline Or Diesel Oil

In-situ remediation of petroleum hydrocarbon has significance to the organic pollution control of soil and groundwater. The main technology form of soil venting, the running parameters and the factors affecting the efficiency of soil venting were studied with column/sandbox test with real soils. The concentration of total volatile organic compounds (TVOC) and carbon dioxide in tailing gas and soil gas were analyzed. The changes of concentration of residual oil in soil and its components were also analyzed. The following conclusions could be drawn:①Compared with air injection from column bottom, air extracting from column top was more efficient. Continuous soil venting was more efficient than pulse soil venting. 89.29% gasoline hydrocarbon in column could be removed by air extracting during 264 h of vapor extracting, with the initial concentration of gasoline hydrocarbon of 35.73 mg/g (6%) and venting velocity of 100 mL/min. 96.30% gasoline hydrocarbon was removed during 96 h when venting velocity was 400mL/min. The increase of soil water could accelerate the remediation of sand soil contaminated by gasoline.②The value relation between total petroleum hydrocarbon (TPH) and TVOC of tailing gas from soil column contaminated by gasoline was linearity. The value of TVOC in soil gas could indicate the concentration of residual TPH in soil. From the comparison of venting remediation time basing on the exponential/logarithm numerical fitting of TVOC in soil gas and that of the exponential numerical fitting of TPH in soil, it showed that the remediation time to reach 90% of gasoline removal (t1/10), estimated by the attenuation of residual gasoline in soil, were exactly the same as the remediation time for TVOC to reach 10ppm (t10ppm) estimated by the attenuation of TVOC in soil gas. For TVOC in soil was easy to monitor, it could be used to estimate the remediation time of soil venting based on the numerical fitting. The concentration of TVOC in soil gas lower than 10ppm meant the end of the remediation process.③The dominant composition of gasoline that attenuation naturally in soil was the fraction whose carbon number was below seven. While under soil venting condition, the fraction of gasoline in soil carbon number below six was removed first. Then the fraction carbon number between seven and ten was removed. And the fraction carbon number above eleven was removed last. The heavier the gasoline component's molecular weight, the later its ratio peak value appeared during soil venting. The venting velocity made no difference to the removal order of the components in gasoline. But the faster venting velocity, the shorter the ratio peak value of each component appeared.④The vertical transfer of diesel in fine sand occurred firstly, and the maximum transfer velocity was 0.609cm/min. Physical soil venting had little effect on the remediation of soil contaminated by diesel. When the initially diesel concentration in soil was 30.96 mg/g, the removal rate of diesel was only 3.90% after 196h continuous soil venting with the venting velocity of 100mL/min.⑤The remediation efficiency of six days of pulse low velocity (8mL/min,8h/d) of soil venting to soil contaminated by diesel (initial concentration was 12.46mg/g) and laid aside for 5 months was 21.57-60.14%, which was higher than that of pure physical soil venting and bio-venting strengthened by composting. The CO2/O2 monitor of tailing gas during soil venting showed that there was the activity of microbe. The minimum removal of diesel estimated by the removal and initial concentration of diesel in sandbox was 164.6 g. In this removal, the removal of volatilization was only 0.52%, the removal of total degradation by organism was 4.26%, andthe removal of un-total degradation by organism was 95.35%.⑥The value of TVOC of soil gas could not reflect the concentration of residual diesel in soil. And the relation between the activity of organism and the concentration of diesel in soil was not evident. The oxygen environment in soil changed and the activity of organism decreased after soil venting. The diesel composition analysis of soil samples showed that the lighter composition of diesel had the priority of removal during soil venting.⑦The venting remediation efficiency, the venting velocity and remediation time of soil contaminated by petroleum varied with the kind of petroleum. There were also significant differences at the aspects of composition changed of petroleum and the action of volatize and biodegrade during soil venting. These results all connected with the composition and characteristics of petroleum contaminants, the transfer and transform of petroleum in soil and the venting environment such as soil environment.