Technical Note Thermally enhanced approaches for bioremediation of hydrocarbon-contaminated soils Amedea Perfumo a , Ibrahim M. Banat a, * , Roger Marchant a , Luigi Vezzulli b a Biotechnology Group, School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, N. Ireland, UK b Department for Study of Territory and its Resources (DIP.TE.RIS.), University of Genoa, Genoa, Italy Received 15 December 2005; received in revised form 3 May 2006; accepted 3 May 2006 Available online 19 June 2006 Abstract Successful remediation of contaminated soils is often limited by the low bioavailability of hydrophobic pollutants, which may slow the process significantly. In this study we investigated the benefits of high temperature in enhancing hydrocarbon degradation rates and eval- uated the effect of different biostimulants. Hexadecane polluted soil microcosms with various amendments were incubated both at 60 °C and room temperature (18 °C) and analyzed periodically up to 40 d for the degradation of hydrocarbon and the response of the microbial population. Natural attenuation showed a satisfactory intrinsic degradative capability at 60 °C and the addition of inorganic N, P and K increased the degradation rates by 10%. The addition of rhamnolipid biosurfactant further enhanced the bioavailability of alkane to microbial degradation resulting in up to 71% removal at 60 °C and 42% at 18 °C. Significant input to hexadecane degradation occurred at 60 °C (70%) as a result of the bioaugmentation with thermophilic Geobacillus thermoleovorans T80, which did not take place at 18 °C. Coupling high temperature to all amendments resulted in 90% removal of the hexadecane from soil after 40 d which was also accompa- nied with an increase in bacterial numbers. The results suggest that thermally enhanced bioremediation may be an efficient technology for the treatment of hydrocarbon-contaminated soils. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Degradation; Hexadecane; Geobacillus thermoleovorans; Thermophilic; Oil contamination 1. Introduction The clean-up of petroleum hydrocarbon-contaminated soils remains a priority task for the restoration of the nat- ural environment due to the serious threat contaminants pose to soil, groundwater and drinking water safety (ASTM, 1995). Among the many techniques employed to remediate polluted sites, environmental friendly technolo- gies of bioremediation are gaining increasing prominence due to their obvious advantages (Head, 1998). A variety of bioremediation methods have been devel- oped to support and increase the degradative activities of native microbial populations (natural attenuation), thus allowing a reduction in time required and subsequent saving in costs. The two main approaches to bioremediation are: (a) environmental biostimulation involving the addition of mainly oxygen and/or mineral nutrients (usually combi- nation of nitrogen, phosphorus and trace metals) and (b) bioaugmentation through the direct application of selected degrader microorganisms to the site (Korda et al., 1997). Several factors, both physico-chemical (e.g., soil charac- teristics, nutrients, oxygen, pH, quality and quantity of the contaminants, history of the pollution) and biological (number and species of indigenous microflora, presence of degrading microorganisms) affect the rate of microbial degradation of hydrocarbons in soil. Among them, temper- ature plays a significant role in controlling bioavailability of low-solubility hydrocarbons and hence the nature and the extent of microbial metabolism (Margesin and Schin- ner, 2001). The rate at which microbial cells can convert contaminants during bioremediation depends on the rate 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.05.006 * Corresponding author. Tel.: +44 2870323062; fax: +44 2870324965. E-mail address: IM.Banat@ulster.ac.uk (I.M. Banat). www.elsevier.com/locate/chemosphere Chemosphere 66 (2007) 179–184