Biosurfactant-Enhanced Remediation of Oil-Contaminated Groundwater

Abstract

Abstract Groundwater contaminated with hydrocarbons poses a serious hazard to the environment. Current oil-contaminated groundwater remediation techniques include physical, chemical, and biological approaches. Chemical surfactants have the potential of high toxicity due to their low biodegradability. Biosurfactants have demonstrated similar performance to that of chemical surfactants, with the added value of low toxicity. The use of surfactants directly over the top layer of crude oil-contaminating groundwater, where environmental conditions are different from that in above ground surfaces, have yet not been explored in depth. Therefore, this study aims to investigate the potential of four different surfactants for their ability to be deployed in conditions mimicking underground aquifer so as to enhance remediation of oil-contaminated groundwater. Selected surfactants comprised two chemical surfactants, referred to as A and B, and two biosurfactants, referred to as BS and C. Surfactants were evaluated for their ability (i) to reduce the crude oil layer thickness through facilitating oil dispersion, and (ii) the extent of natural biodegradation it can achieve. Experiments were performed in glass flasks containing synthetic groundwater and crude oil supplemented with surfactant added at the three different surfactants: oil ratios (S:O) 1:5, 1:10 and 1:50. Reduction of crude oil layer thickness, water turbidity, and bacterial cell count were continuously monitored for 60 days to observe the temporal variation of biosurfactant activity towards crude oil. The performance of surfactants A, C and BS in reducing oil layer thickness was influenced by temperature and S:O ratios. Overall, increase in temperature increased the performance of these three surfactants. S:O ratio was optimal at 1:10 for surfactants A and BS, and at 1:5 for surfactant C. Surfactants A and C reduced the oil layer thickness mainly by means of dispersion and less by biodegradation. In contrast, surfactant BS exhibited an increase in bacterial cell growth that is directly correlated to oil thickness reduction, with an almost equal contribution in the crude oil removal by both dispersion and biodegradation. Considering our findings, it is of high relevance to apply biosurfactants under optimal conditions to enhance the performance of surfactants in crude-oil removal. This study suggests that in order to develop an effective in-situ biosurfactant-based remediation system for oil decontamination of aquatic environments, different parameters should be considered. Such parameters play an important role in treatment feasibility.