Surfactant foam technology for in situ removal of heavy chlorinated compounds-DNAPLs

The use of surfactant foam for the remediation of a saturated soil contaminated with a dense non-aqueous phase liquid (DNAPL) was investigated at bench-scale. Despite the presence of the DNAPL, high foam stability was obtained for a mixture of cocamidopropyl betaïne and dodecylsulfate at 0.05%. Foams were assessed in different injection conditions and were compared to commonly used remediation methods. Strong foams improved significantly the DNAPL recovery yield, which amounted up to 98%, owing to the propagation of a flat foam front, with low dissolution (<0.5 g l(-1)) and surfactant consumption (<10 g kg(-1) DNAPL recovered). The effects of important parameters (gas to liquid ratio, injection velocity, gas nature) and methods for foam production on pressure gradient (∇P), remediation efficiency and surfactant consumption were investigated. Even for low injection velocities (4×10(-4) ms(-1)), capillary numbers were high enough (∼8×10(-3)) to push the DNAPL efficiently. DNAPL lowered ∇P for foam propagation because of its destabilising effect. The use of CO2 as gas reduced the ∇Ps for foam propagation by 35%. ∇P were also decreased by 25% for gas to liquid ratios lower than 75%, whereas, DNAPL removal remained high. This technology should lower spreading risks and treatment costs.