Heavy metal removal from sediments by biosurfactants

Batch washing experiments were used to evaluate the feasibility of using bi osurfactants for the removal of heavy metals from sediments. Surfactin from Bacillus subtilis, rhamnolipids from Pseudomonas aeruginosa and sophorolip id from Torulopsis bombicola were evaluated using a metal-contaminated sedi ment (110 mg/kg copper and 3300 mg/kg zinc). A single washing with 0.5% rha mnolipid removed 65% of the copper and 18% of the zinc, whereas 4% sophorol ipid removed 25% of the copper and 60% of the zinc. Surfactin was less effe ctive, removing 15% of the copper and 6% of the zinc. The technique of ultr afiltration and zeta potential measurements were used to determine the mech anism of metal removal by the surfactants. It was then postulated that meta l removal by the biosurfactants occurs through sorption of the surfactant o n to the soil surface and complexation with the metal, detachment of the me tal from the soil into the soil solution and hence association with surfact ant micelles. Sequential extraction procedures were used on the sediment to determine the speciation of the heavy metals before and after surfactant w ashing. The carbonate and oxide fractions accounted for over 90% of the zin c present in the sediments. The organic fraction constituted over 70% of th e copper. Sequential extraction of the sediments after washing with the var ious surfactants indicated that the biosurfactants, rhamnolipid and surfact in could remove the organically-bound copper and that the sophorolipid coul d remove the carbonate and oxide-bound zinc. Therefore, heavy metal removal from sediments is feasible and further research will be conducted. (C) 200 1 Elsevier Science B.V. All rights reserved.