Elevated critical micelle concentration in soil–water system and its implication on PAH removal and surfactant selecting

Abstract

Triton X-100 (TX100) and Brij 35 (B35) were used to investigate the elevated critical micelle concentration (CMC) induced by surfactant sorption and its influence on PAH removal in soil washing systems. The surface tension technique was applied to determine the CMC and the apparent CMC (CMCsoil) in soil–water systems. Surfactant sorption experiments were conducted by the batch equilibration technique. Surfactants sorbed on the soil at concentrations below the CMCsoil were quantified with data from the surface tension experiments for both an aqueous system and a soil–water system. Due to sorption, the CMCsoil values of the two surfactants are 2.75 and 6.31 times their corresponding CMC values in aqueous solutions, respectively. At concentrations below CMCsoil, the loss of B35 (92–99.7 %) was greater than that of TX100 (63–92 %). The PAH removal efficiencies are greatly dependent on the CMCsoil value. At surfactant concentrations below CMCsoil, the PAH removal is very low and remains almost invariable. Whereas, at concentrations above CMCsoil, the PAH removal increases greatly. B35 inhibited PAH desorption at concentrations below its CMCsoil. For TX100, some degree of PAH desorption enhancement was observed at concentrations below its CMCsoil. CMCsoil is a key parameter while selecting a surfactant for a specific soil washing system, only surfactant concentrations above their CMCsoil should be evaluated.