Enhanced Soil Washing For PAHs-contaminated Soils By Sapindus Saponin And Recovery Of Washed Surfactant Solution

Surfactant-enhanced remediation has been suggested as a promising technology for the remediation of organic-contaminated soils. Biosufactants have been used in enviromental application to enhance solubility of organic components for soil washing or flushing due to their typical desirable properties including solubility enhancement, surface tension reduction, biodegradabilities and enviromentally friendly nature. In this paper, the application of biosurfactants for the remediation of PAHs-contaminated soils and the corresponding mechanisms were reviewed. First, Sapindus saponin, extracted from the fruit pericarp of Sapindus mukorossi Gaerth, was studied in enhancing solubilization and soil washing for phenanthrene. Then, the treatment and recovery of washed surfactant solutions by organo-bentonite was studied. The main original conclusions are drawn as follows:(1) It was found that Sapindus saponin, extracted from the fruit pericarp of Sapindus mukorossi Gaerth, could effectively remove phenanthrene from contaminated soil with a maximum removal percentage of about85-89%, slightly lower than Tween80. The low solution pH is favorable for Sapindus saponin in enhancing phenanthrene solubilization and adsorption onto the soil. The removal percentages of phenanthrene increased at first and then decreased with the increasing of solution pH. And the maximum washing effiiciency for phenanthrene from contaminated soil was obtained at pH6.0around.(2) An alternative approach using organo-bentonite to recover washed surfactant solutions was developed. It was found that PAHs can be effectively removed by organo-bentonite from surfactant solutions in a high proportion relative to the sorption loss of surfactant. The physicochemical properties of PAHs, surfactant hydrophilicity and surfactant concentration, the repeated times of organo-bentonite had effect on the selectivity parameter for PAHs removal to surfactant sorption loss. Surfactant recovery is more feasible for the surfactant with lower aqueous concentration, higher hydrophilicity, or containing PAHs with higher hydrophobicity. The repeated usage of organo-bentonite is favorable for increasing the performance of selective sorption for surfactant recovery and reducing the operation costs for the post-treatment or surfactant recovery after soil washing process.