Coupling surfactants with ISCO for remediating of NAPLs: Recent progress and application challenges

Non-aqueous phase liquids (NAPLs) pose a serious risk to the soil-groundwater environment. Coupling surfactants with in situ chemical oxidation (ISCO) technology is a promising strategy, which is attributed to the enhanced desorption and solubilization efficiency of NAPL contaminants. However, the complex interactions among surfactants, oxidation systems, and NAPL contaminants have not been fully revealed. This review provides a comprehensive overview on the development of surfactant-coupled ISCO technology focusing on the effects of surfactants on oxidation systems and NAPLs degradation behavior. Specifically, we discussed the compatibility between surfactants and oxidation systems, including the non-productive consumption of oxidants by surfactants, the role of surfactants in catalytic oxidation systems, and the loss of surfactants solubilization capacity during oxidation process. The effect of surfactants on the degradation behavior of NAPL contaminants is then thoroughly summarized in terms of degradation kinetics, byproducts and degradation mechanisms. This review demonstrates that it is crucial to minimize the negative effects of surfactants on NAPL contaminants oxidation process by fully understanding the interaction between surfactants and oxidation systems, which would promote the successful implementation of surfactant-coupled ISCO technology in remediation of NAPLs-contaminated sites.