Remediation of DNAPL-contaminated aquifers using density modification method with colloidal liquid aphrons

Abstract Entrapped and pooled dense non-aqueous phase liquid (DNAPL) often persists in aquifers and serves as a long-term source of groundwater contamination. Despite vigorous research efforts over the last two decades, all current DNAPL pool remediation strategies suffer from a combination of inefficiency, enhanced risk of contaminant spreading due to uncontrolled mobilization, and or high treatment costs. In the present contribution, we report a novel strategy that makes the density of the representative DNAPL of trichloroethene (TCE) reduction utilizing colloidal liquid aphrons (CLAs) in the remediation process. The effects of the electrolyte (AlCl 3 ) concentrations, the volume fraction of the dispersed oil phase ( n -octane) and temperature on the demulsification behavior of CLA dispersion were discussed. Steady-state flow and dynamic viscoelasticity were measured by using a controlled stress rheometer HAAKE RS 6000 with cone-plate geometry in an attempt to reveal the rheological properties of CLAs. A series of batch experiments was conducted to evaluate the recovery efficiency of DNAPL from sand pack under different volumes, flow rates of CLAs and surfactant (Tergitol 15-S-9) flushing solutions. Experimental results suggest that CLAs can be destabilized by a low concentration of Al 3+ in the continuous phase. The flow behavior of CLAs presents the typical non-Newtonian liquids with strong shear thinning properties and it could be well described by the Hershel–Bulkley model. Above the phase volume ratio (PVR =  V org / V aq ) of 8, the systems display viscoelastic behavior. Relative to water, the density reversal of TCE occurs at an electrolyte concentration of 0.05 M, which effectively prevents TCE downward migration during surfactant flushing. As much as 94% of the TCE entrapped in the sand column is removed under the conditions of amounts of 1 PV (pore volume) for CLAs, 4 PV and 1.5 mL/min for Tergitol solution. This approach holds great promise for manipulating DNAPL densities prior to or during remediation processes.