Study On Influencing Factors Of Thermally-Enhanced Soil Vapor Extraction On Remediation Of Soil Contaminated By Semi-volatile Linear Hydrocarbon

With the rapid development of petroleum exploitation and petrochemical industry,the site contaminated by petroleum hydrocarbons is gradually increasing.There is the advantage of economy,high efficiency and great maneuverability by using soil vapor extraction technology to remediate the soil contaminated by petroleum hydrocarbons.Thermally-enhanced soil vapor extraction is capable of remediating soil polluted by petroleum hydrocarbons with higher boiling point.In order to better guide the actual remediation of petroleum hydrocarbon contaminated soils on-site,researches on the mechanism of remediation of soil polluted by petroleum hydrocarbon under the operation of thermally-enhanced soil vapor extraction,further on expanding the scope of application as well as optimizing corresponding engineering technical parameters of the technology is pretty urgent.In laboratory,thermally-enhanced soil vapor extraction device with two dimensions was set up.The device was composed of soil column,temperature control and heating system,gas extraction and circuit system and sensor monitoring system.The prepared sandy-soil contaminated by undecanone,tridecane,tetradecane,pentadecane and hexadecane was put in the column,simulating of remediation process by using thermally-enhanced soil vapor extraction on-site.The experiment was carried out on the remediation of soil contaminated by semi-volatile straight chain hydrocarbon at normal atmospheric temperature and under thermally-enhanced condition,and further on the impact of soil moisture and organic matter on remediation efficiency under thermally-enhanced condition.At normal atmospheric temperature(unheated status),the volatility of n-alkanes in sandy soils was very low,and thus the concentration of the n-alkanes in extracted gas kept constant at the lower level.However,the operation of thermally-enhanced soil vapor extraction for consecutive six days made the concentration of n-alkanes in soils decreased significantly.The distribution of n-alkanes was determined by temperature field within the soil column.The greater the soil temperature,the lower the n-alkane residual level.It was observed that under heating condition,the temperature distribution within soil column is funnel-shaped,and the closer to the heat source,the faster the soil temperature rose.The data collected by temperature sensors was well simulated by CMG-STARS software.Thermally-enhanced operation increased the vapor pressure of n-alkanes in soils,and thus promoted the distribution of the contaminants to extracted gas.In the process of soil remediation by using thermally-enhanced soil vapor extraction,soil temperature under higher moisture for the first and second day rose slowly.The increase of moisture obviously inhibited the migration of n-alkanes with high boiling point to soil gas phase.When moisture was kept at higher level,thermally-enhanced soil vapor extraction made water vapors continuously converge near the inlet of extraction well.Due to the transpiration and heat dissipation processes,the soil temperature within 10 cm around the inlet of well was always low which made the distribution ratio of n-alkanes to soil gas was decreased.In the process of soil remediation by using thermally-enhanced soil vapor extraction,the increment of soil organic matter significantly limited the migration of mass transfer of n-alkanes in soil and thus migration to gas phase.In the soils with less organic matter,migration rate of n-alkanes to soil gas phase was depended on their vapor pressure and soil concentration.When soil organic matter was increased,more n-alkanes were migrated into soil organic fraction,and the migration velocity of these contaminants was mainly determined by soil organic matter/air partition coefficient.The increase of soil organic matter made the volatilization of n-alkanes delayed,and thus residual level of the pollutants rose.