Aggression and depletion of residual organic phase in contaminated porous media: In-situ microemulsification approach

Conventional Pump and Treat (P&T) for aquifer remediation fails to achieve quality goals within sustainable times and costs, especially in the presence of trapped residual free organic phase. Nowadays, numerous technologies are available to target contamination sources. Among these, SEAR (surfactant-enhanced aquifer remediation) technology is attracting considerable interest thanks to the mobilizing and solubilizing properties of surfactants. Particularly, the transformation of immiscible organic phases into microemulsions, directly within the porous medium, accelerates clean-up times and reduces the long-term persistence of contamination sources, thereby limiting the risk of groundwater recontamination. This work proposes a novel aquifer remediation strategy investigating the ability of two anionic alkyl-sulfosuccinate surfactants to form in-situ microemulsions with an organic phase, consisting of toluene or trichloroethylene (TCE). After determining the optimal conditions under which the surfactants form microemulsions with the reference contaminants, a column configuration test was performed, simulating under laboratory-controlled conditions a soil flushing process to directly evaluate the ability of the surfactant’s formulations to quantitatively deplete the residual organic fraction through the in-situ microemulsification mechanism. Experimental results highlight the surfactants’ great capability to generate stable microemulsions with organic pollutants in pure organic phase under specific salinity conditions, always below 5 % wt of NaCl. The in-situ microemulsification mechanism has proven to be very effective for the depletion of secondary contamination sources, promoting the removal of over 95 % of the organic phase, requiring a minimal pore volume of formulation.