Remediation of toluene-contaminated soils by sequential treatment: Soil vapor extraction systems and internal combustion engine units

Abstract

This paper reports soil vapor extraction (SVE) systems and internal combustion engine (ICE) units to remediate soils contaminated with toluene. Response surface methodology (RSM) was used to evaluate the influence of toluene concentration, air flow rate and soil water content on SVE systems, thus to identify the optimal conditions for SVE systems. ICE units were used to treat the SVE off-gas extracted from toluene-contaminated soils, and the performance in removing toluene was effectively evaluated. Furthermore, the pulsed operation of SVE systems and the thermal enhancement with ICE off-gas were explored, and the positive effects on remediation efficiency were analyzed. The remediation experiments performed in toluene-contaminated soils allowed concluding that the optimal desorption time of toluene was 615 min with the toluene concentration of 0.3 g/kg, air flow rate of 10 L/min and soil water content of 9 %. The ICE units showed that the main components of ICE off-gas were CO, CO₂ and hydrocarbon (HC). After 25 min, the concentration of HC decreased to 140 ppm, and the volume fractions of CO and CO₂ were 0.3 % and 9.5 % respectively. ICE units had consistently achieved toluene destruction and removal efficiencies (DREs) of 100 %. Moreover, the pulsed operation and thermal enhancement promoted equilibrium partitioning of toluene between the soil matrix and the gas phase, thereby facilitating the desorption of toluene, which decreased the required time and energy needed for the remediation. This study provides theoretical support for system design and applicability assessment of SVE systems and ICE units in the remediation of contaminated soils.