Enhanced removal of DNAPL trapped in porous media using simultaneous injection of cosolvent with air: influencing factors and removal mechanisms

Factors influencing dense non-aqueous phase liquid (DNAPL) removal by concurrent injection of cosolvent and air were evaluated using micromodels and visualization techniques. Cosolvent (ethanol/water) was injected simultaneously with air into glass micromodels containing residual perchloroethylene (PCE). Impacts of the air flow rates and PCE solubility in the remedial fluid on PCE removal processes were examined. Although two major processes, immiscible displacement and dissolution, may contribute PCE removal from porous media during cosolvent-air (CA) flooding, PCE displacement occurred only in the initial flooding period and was independent of the air flow rate and ethanol content. However, faster airflow through the porous medium improved remedial fluid distribution and dynamics and resulted in enhanced dissolution of the DNAPL. Dissolution rates were directly related to PCE solubility in the remedial fluid. Enhanced contact between cosolvent and DNAPL during CA flooding was observed in a non-homogeneous micromodel with random flow paths.