Metal Removal from Contaminated Soil and Sediments by the Biosurfactant Surfactin

Abstract

Batch soil washing experiments were performed to evaluate the feasibility of using surfactin from Bacillus subtilis, a lipopeptide biosurfactant, for the removal of heavy metals from a contaminated soil and sediments. The soil contained high levels of metals and hydrocarbons (890 mg/kg of zinc, 420 mg/kg of copper, and 12.6% oil and grease), and the sediments contained 110 mg/kg of copper and 3300 mg/kg of zinc. The contaminated soil was spiked to increase the levels of copper, zinc, and cadmium to 550, 1200, and 2000 mg/kg, respectively. Water alone removed minimal amounts of copper and zinc (less than 1%). Results showed that 0.25% surfactin/1% NaOH could remove 25% of the copper and 6% of the zinc from the soil and 15% of the copper and 6% of the zinc from the sediments. A series of five washings of the soil with 0.25% surfactin (1% NaOH) was able to remove 70% of the copper and 22% of the zinc. The technique of ultrafiltration and the measurement of octanol−water partitioning and ζ-potential were used to determine the mechanism of metal removal by surfactin. It was indicated that surfactin was able to remove the metals by sorption at the soil interphase and metal complexation, followed by desorption of the metal through interfacial tension lowering and fluid forces and finally complexation of the metal with the micelles.