A laboratory study of surfactant flushing of DNAPL in the presence of macroemulsion.

Computed tomography (CT) monitored experiments are conducted in a three-dimensional water-saturated sandpack to evaluate the performance of a biodegradable surfactant (Glucopon-425N) in recovering a residually trapped dense nonaqueous phase liquid (DNAPL) tetrachloroethylene (PCE) from two sandpacks. Effects of flow rate, surfactant concentration, and pore size on the remediation process are evaluated. Axial variation in porosity of a sandpack has significant effect on the residual distribution of DNAPL in the sandpack and its subsequent recovery. DNAPL is recovered in two stages in general: mobilization followed by macroemulsion-solubilization. Mobilized DNAPL is recovered as a free-phase for all the experiments in the 30-mesh sandpack and only limited mobilization was observed in the 50-mesh sandpack. The dominant mechanism of recovery is macroemulsion flow (accounts for 46-86% of solubilized-emulsified PCE) in both the sands which leads to much higher PCE effluent concentration than the solubility limit as determined in batch solubilization studies. The effluent PCE concentration in the later stage depends on surfactant concentration but not on surfactant flow rate or pore size.