Emulsion-based recovery of a multicomponent petroleum hydrocarbon NAPL using nonionic surfactant formulations

Surfactants can aid subsurface remediation through three primary mechanisms - solubilization, mobilization and/or emulsification. Among these mechanisms, emulsification in porous media is generally not well studied or well understood; particularly in the context of treating sources containing multicomponent NAPL. The objective of this research was to elucidate the processes responsible for recovery of a multicomponent hydrocarbon NAPL when surfactant solutions are introduced within a porous medium to promote the formation of kinetically-stable oil-in-water emulsions. Emulsifier formulations considered here were selected to offer similar performance characteristics while relying on different families of non-ionic surfactants - nonylphenol ethoxylates or alcohol ethoxylates - for emulsification. The families of surfactants have particular environment relevance, as alcohol ethoxylates are often used where replacement of nonylphenol content is necessary. Results from batch and column studies suggest performance of the two formulations was similar. With both, a synergistic combination of emulsification and mobilization led to recovery of a synthetic gasoline NAPL. The relative contribution of solubilization to the recovery was found to be minor. Moreover, the physical processes associated with emulsification and mobilization acted to limit the amount of preferential recovery (or fractionation) of the multicomponent NAPL.