Thermally Enhanced Bioremediation of NAPL Polluted Soil-Water Resources

Abstract

The use of conventional techniques for physico-chemical remediation of hydrocarbon such non-aqueous phase liquids (NAPL)-polluted sites may disturb the natural biotic settings of the (sub)-surface. However, natural attenuation has been reported very slow and sometime results as incomplete removal under prevailing site conditions. In particular, microbial growth is quite slow in cold regions, which reduces the applicability of bioremediation in treating NAPL-polluted soil-water. Thus, this study aims to evaluate the thermally enhanced bioremediation techniques to treat NAPL-polluted soil-water using practical experiments. A one-dimensional large column setup was designed and fabricated for this purpose. The column was integrated with automatic temperature controlling baths to maintain different soil-water temperatures (4 °C, 20 °C, 28 °C, and 36 °C), which was circulated through the porous media filled in the column setup. Results show a high dissolution rate of toluene, the selected light NAPL, at an elevated temperature of 28–36 °C. The biodegradation rates of the NAPL were found to be 0.002 mg L/h, 0.008 mg L/h, 0.012 mg L/h, and 0.015 mg L/h at soil-water temperature levels of 4 °C, 20 °C, 28 °C, and 36 °C, respectively. It was found that at high soil-water temperature (28 °C and 36 °C), a significant increment in microbial actions accelerates the biodegradation rate of NAPL in the subsurface system. The outcomes of this study may help in treating NAPL-polluted sites using solar or geo-thermal based heating systems for thermally enhanced bioremediation.