An increase in energy demand leads to further exploration,transportation,and utilization of petroleum,which creates severe soil contamination because of recurrent accidents and oil spills.Remediation of these contaminated soils is challenging.Among many treatment methods practiced for remediation of petroleum-contaminated soils,surfactant-enhanced soil washing has been widely practiced as a preferred treatment option,as it is a fast and environmentally accepted method.In this paper,we review research undertaken on various anionic,nonionic,cationic,biological,and mixed surfactants for the remediation of petroleum hydrocarbon-contaminated soils.Upcoming surfactants like gemini and switchable surfactants are summarized.We assess the challenges and opportunities of in-situ and ex-situ soil washing,the mechanisms of surfactant-enhanced soil washing,and the criteria to follow for surfactant selection.Furthermore,we briefly discuss the operational and environmental factors affecting soil washing efficiency and soil and surfactant properties affecting surfactant adsorption.We also describe the advantages of coupling soil washing with effluent treatment and surfactant reuse challenges and opportunities.Moreover,challenges and possible new directions for future research on surfactant-enhanced soil washing are proposed.
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