The effect of temperature on the bioventing of soil contaminated with toluene and decane

The effect of temperature on evaporation and biodegradation rates during so il bioventing (SBV) was studied for a mixture of toluene and decane in benc h-scale soil columns at a continuous air flow and consecutively at two diff erent flow rates. The effect of temperature on SBV was monitored by GC head space analysis of contaminant, CO2 and O-2 concentrations in the soil gas o ver time. Separation of evaporation and biodegradation processes into three different phases based on their rates was used together with Q(10) and E-1 0 (values that give the factor by which biodegradation and evaporation rate s increase when the temperature is raised by 10 degrees) to compare quantit atively the removal kinetics at 10 and 20 degrees C. Adsorption of toluene and decane onto soil (a phase partitioning process) at 20 and 10 degrees C was described with linear Freundlich isotherms. A temperature decrease from 20 to 10 degrees C resulted in an increase of soil-air partitioning coeffi cients by a factor of 1.8 and of 2.1 for toluene and decane, respectively. The mean Q(10) value for the biodegradation of toluene was found to be 2.2 fora temperature rise from 10 to 20 degrees C. A toluene content in the soi l gas above 75% of the saturation concentration inhibited biodegradation at both temperatures. The SBV efficiency was dependent on temperature with re spect to remediation time. SBV at 20 degrees C resulted in a 99.8% and a 98 .7% reduction of toluene and decane initial concentrations, respectively. T o reach similar results at 10 degrees C, about 1.6 times as much time and 1 .4 times as much air were required; however, at both temperatures the total amounts of biodegraded hydrocarbons were approximately the same. The evapo ration-to-biodegradation ratios at 20 degrees C were 82.5:17.5 for toluene and 16:84 for decane, whereas at 10 degrees C they were 71:29 and 2:98, res pectively. A comparison of Q(10) values showed that, except during the init ial phase of SBV only a modest decrease in biodegradation rates should be e xpected after a decrease in temperature from 20 to 10 degrees C. Flow rate reduction had a significant impact on the toluene evaporation rate at a hig her temperature, whereas for decane this rate was only slightly affected by temperature. In contrast to decane, the ratio between toluene vapor pressu res at 20 and 10 degrees C maybe used to predict the removal of toluene by evaporation during the above-mentioned phases of SBV, when evaporation is i mportant.