Combining solvent extraction and bioremediation for removing weathered petroleum from contaminated soil

This study aimed to remediate a highly contaminated soil with weathered petroleum using an integrated technology combining solvent extraction and biodegradation. Soils were washed using a composite organic solvent consisted of hexane and pentane (4:1 v/v) and then bioremediated in microcosms which were bioaugmentated with Bacillus subtilis FQ06 strains and/or rhamnolipid. The optimal solvent extraction conditions were determined as extraction for 20 min at 25 °C with solvent-soil ratio of 6:1 (v/w). On this basis, total petroleum hydrocarbon was decreased from 140,000 to 14,000 mg kg-1, which was further reduced to < 4000 mg kg-1 by subsequent bioremediation for 132 days. Sustainability assessment of this integrated technology showed its good performance for both short- and long-term effectiveness. Overall results encouraged its application for remediating contaminated sites especially with high concentration weathered hydrocarbons.