AQUIFER WASHING BY MICELLAR SOLUTIONS - 2 - DNAPL RECOVERY MECHANISMSFOR AN OPTIMIZED ALCOHOL-SURFACTANT-SOLVENT SOLUTION

A large sand column experiment is used to illustrate the principles of complex organic contaminants (DNAPL) recovery by a chemical solution containing an alcohol (n-butanol), a surfactant (Hostapur SAS), and tw o solvents (d-limonene and toluene). The washing solution is pushed by viscous polymer solutions to keep the displacement stable. The main N APL recovery mechanisms identified are: (1) immiscible displacement by oil saturation increase (oil swelling), oil viscosity reduction, inte rfacial tension lowering, and relative permeability increase; (2) misc ible NAPL displacement by solubilization. Most of the NAPL was recover ed in a Winsor, type TT system ahead of the washing solution. The 0.8 pore volume (PV) of alcohol-surfactant-solvent solution injected recov ered more than 89% of the initial residual DNAPL saturation (0.195). W insor system types were determined by visual observation of phases and confirmed by electrical resistivity measurements of phases and water content measurements in the oleic phase. Viscosity and density lowerin g of the oleic phase was made using solvents and alcohol transfer from the washing solution. Small sand column tests are performed to check different rinsing strategies used to minimize washing solution residua l ingredients which can be trapped in sediments. An alcohol/surfactant rinsing solution without solvent, injected behind the washing solutio n, minimizes solvent trapping in sediments, More than five pore volume s of polymer solution and water must be injected after the rinsing sol ution to decrease alcohol and SAS concentrations in sediments to an ac ceptable level. To obtain reasonable trapped surfactant concentrations in sediments, the displacement front between the rinsing solution and the subsequent the following polymer solution has to be stable. (C) 1 998 Elsevier Science B.V.