Thermally enhanced approaches for bioremediation of hydrocarbon-contaminated soils

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 evaluated 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 accompanied 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.