Effect of biosurfactants on crude oil desorption and mobilization in a soil system Maria S. Kuyukina a, * , Irena B. Ivshina a , Sergey O. Makarov b,1 , Ludmila V. Litvinenko b,1 , Colin J. Cunningham c,2 , James C. Philp d,3 a Institute of Ecology and Genetics of Microorganisms, Ural Branch of the Russian Academy of Sciences, 13 Golev Street, Perm 614081, Russia b Perm State University, 15 Bukirev Street, Perm 614000, Russia c Contaminated Land Assessment and Remediation Research Centre (CLARRC), Faraday Building, The King’s Buildings, University of Edinburgh, Edinburgh EH9 3JL, Scotland, UK d School of Life Sciences, Napier University, 10 Colinton Road, Edinburgh EH10 5DT, Scotland, UK Available online 5 November 2004 Abstract Microbially produced biosurfactants were studied to enhance crude oil desorption and mobilization in model soil column systems. The ability of biosurfactants from Rhodococcus ruber to remove the oil from the soil core was 1.4–2.3 times greater than that of a synthetic surfactant of suitable properties, Tween 60. Biosurfactant-enhanced oil mobilization was temperature-related, and it was slower at 15 8C than at 22–28 8C. Mathematical modelling using a one-dimensional filtration model was applied to simulate the process of oil penetration through a soil column in the presence of (bio)surfactants. A strong positive correlation (R 2 =0.99) was found between surfactant penetration through oil-contaminated soil and oil removal activity. Biosurfactant was less adsorbed to soil components than synthetic surfactant, thus rapidly penetrating through the soil column and effectively removing 65–82% of crude oil. Chemical analysis showed that crude oil removed by biosurfactant contained a lower proportion of high-molecular-weight paraffins and asphaltenes, the most nonbiodegradable compounds, compared to initial oil composition. This result suggests that oil mobilized by biosurfactants could be easily biodegraded by soil bacteria. Rhodococcus biosurfactants can be used for in situ remediation of oil-contaminated soils. D 2004 Elsevier Ltd. All rights reserved. Keywords: Biosurfactants; Bacteria; Rhodococcus ; Crude oil; Soil; Desorption; Mobilization; Mathematical modelling 1. Introduction In natural conditions, oil penetration through soil is an extremely complex process involving physical, chemical, and biological factors. Crude oil is a highly hydrophobic material with most of its components having low water solubility. These components bind to soil particles and become nonbioavailable to microorganisms. To increase the bioavailability of hydrocarbon pollutants, surface-active agents (surfactants) may be used, allowing desorption and solubilization of petroleum hydrocarbons and thus facilitat- ing their assimilation by microbial cells (Deshpande et al., 1999; Doong and Lei, 2003; Mulligan et al., 2001). There are two mechanisms of surfactant-enhanced soil washing. One occurs below the critical micelle concentration (CMC), when surfactant monomers increase the contact angle between the soil and hydrophobic contaminant, thereby promoting the separation of contaminant from soil particles and finally displacing the oil from the soil (soil roll-up mechanism). The other mechanism, solubilization, occurs above the CMC, when contaminants are partitioned from the 0160-4120/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2004.09.009 * Corresponding author. Tel.: +7 3422 446714; fax: +7 3422 446711. E-mail addresses: kuyukina@iegm.ru (M.S. Kuyukina)8 ivshina@iegm.ru (I.B. Ivshina)8 som@psu.ru (S.O. Makarov)8 c.cunningham@ed.ac.uk (C.J. Cunningham)8 J.Philp@napier.ac.uk (J.C. Philp). 1 Tel.: +7 3422 39 66 26; fax: +7 3422 39 68 69. 2 Tel.: +44 131 650 7327; fax: +44 131 650 7328. 3 Tel.: +44 131 455 2462; fax: +44 131 455 2291. Environment International 31 (2005) 155 – 161 www.elsevier.com/locate/envint