Feasibility evaluation of novel anionic-nonionic gemini surfactants for surfactant-enhanced aquifer remediation

Surfactant-enhanced aquifer remediation (SEAR) can effectively remove residual dense non-aqueous phase liquids. In this work, a series of environment-friendly anionic-nonionic gemini surfactants, namely, ethylene glycol succinate polyoxyethylene sulfonate (GEOnS-m, n = 3, 5 and 7; m = 10 and 12), were synthesized and evaluated for application in SEAR. The critical micelle concentrations of GEOnS-m were 2.14 × 10−3–1.62 × 10−2 mM, and the molar solubilization ratios of GEOnS-m for tetrachloroethylene were 1.93–3.44, which were 1.5–5 times higher than traditional surfactants. The GEOnS-m solutions remained stable at 5–25 °C, 50 mM salt, and pH = 5.0–9.0. The micelle size decreased as the temperature decreased, which reduced the solubilization capacity (24.9%–37.0%) of the GEOnS-m solutions. Inorganic salts could improve the solubilization capacity of the GEOnS-m solutions by promoting micelle polymerization and increasing the hydrophobic core volume for solubilizing tetrachloroethylene. This work found that 0.80%–4.00% of GEOnS-m adsorbed on the media during simulated column flushing, which was less than the traditional surfactants due to stronger electrostatic repulsion between the micelles and the media. Meanwhile, the solubilization capacity of GEOnS-m was positively correlated with the hydrophobic carbon chain length, while, the adsorption amount in the media and application cost of GEOnS-m were positively correlated with the EO number and negatively correlated with the hydrophobic carbon chain length. Comprehensive evaluation results revealed that GEO3S-12 was preferred for SEAR. This work not only developed suitable surfactants for SEAR but also attempted to further the rational design of surfactants for diverse applications by combining different functional groups into one molecule.