Selective adsorption of phenanthrene in nonionic–anionic surfactant mixtures using activated carbon

Surfactant enhanced soil washing is an efficient remediation process for sites contaminated with hazardous hydrophobic organic compound (HOC). To reduce the cost of the process, the used surfactant should be recovered. This paper presents investigation of selective adsorption of HOC in nonionic–anionic surfactant mixtures by activated carbon as a means of recovering surfactants, using phenanthrene (PHE) as an HOC, Triton X-100 (TX100) as a nonionic surfactant, and sodium dodecyl sulfate (SDS) as an anionic surfactant. The sorbed amount of TX100 on activated carbon decreased from 0.433 to 0.227 mmol/g as SDS dose increased. However the sorbed amount of PHE increased from 0.125 to 0.178 mmol/g as SDS dose increased because molar solubilization ratio of the surfactant mixtures decreased. As a result, selectivity for PHE sorption that represents the ratio of PHE partitioning to surfactant partitioning increased with increase in the proportion of SDS in the surfactant mixture. Selectivity for PHE to surfactant was much higher than 1 over a wide range of surfactant composition. The highest selectivity, 95.97 ± 49.94 at 5.61 × 10−2 mmol-PHE/L, was obtained in the solution containing only SDS. These results suggest that addition of anionic surfactant may improve surfactant recovery when selective adsorption for surfactant recovery is included in soil remediation by surfactant enhanced soil washing.