Thermally Enhanced Bioremediation of NAPL Polluted Soil-Water Resources

Brijesh Kumar Yadav,Pankaj Kumar Gupta

doi:10.3390/pollutants2010005

Brijesh Kumar Yadav, Pankaj Kumar Gupta

Open Access

https://doi.org/10.3390/pollutants2010005

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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.

Highlights

Received: 13 August 2021Sandy aquifer regions are at high risk of hydrocarbon contamination in and around areas of oil-handling activities
Leakage of LNAPLs presents a major risk to ecosystems as they can result in widespread pollution from small spillages, while DNAPL can persist in subsurface for a long time
The LNAPL pool retained around the capillary fringe and groundwater table dissolves with groundwater and subsequently moves to surrounding locations due to advection, diffusion, and dispersion mechanisms of mass transport [1,2,3]

Summary

Introduction

Sandy aquifer regions are at high risk of hydrocarbon contamination in and around areas of oil-handling activities Hydrocarbons such as nonaqueous phase liquids (NAPLs) are of particular concern under varying environmental conditions because of their high sensitivity to subsurface variability, which enables them to spread widely in the subsurface [1,2]. NAPLs are not freely miscible in water, but a small quantity of NAPLs dissolved with water is sufficient to seriously degrade its quality. Based on their density, NAPLs are classified as light and dense NAPLs, known as LNAPLs and DNAPLs, respectively [3].

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