On the use of biosurfactants for the removal of heavy metals from oil‐contaminated soil

Abstract

Abstract The feasibility of using biodegradable biosurfactants to remove heavy metals from an oil‐contaminated soil was evaluated by batch washes with surfactin, a rhamnolipid and a sophorolipid. The soil contained 890 mg/kg of zinc and 420 mg/kg of copper with a 12.6% oil and grease content. Highest levels of zinc removal were obtained using 12% rhamnolipid (19.5% of the zinc) and 4% sophorolipid/0.7% HCl (15.8% of the zinc). Highest copper removal rates were achieved (greater than 25%) with 12% rhamnolipid or with 2% rhamnolipid /!% NaOH or 0.25% surfactin/1% NaOH. A series of five batch washes removed 70% of the copper with 0.1% surfactin/1% NaOH ivhile 4% sophorolipid/0.7% HCl was able to remove 100% of the zinc. Sequential extraction procedures showed that the carbonate and oxide fractions accounted for over 90% of the zinc present in the soil and the organic fraction in the soil constituted over 70% of the copper. Sequential extraction of the soil after washing with the surfactin or rhamnolipid (both with 1% NaOH) indicated that these surfactants could remove the organically‐bound copper and that the sophorolipid with acid could remove the carbonate and oxide ‐bound zinc. In conclusion, the results clearly indicated the feasibility of removing the metals with the anionic biosurfactants tested even though the exchangeable metal fractions were very low.