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 betaine 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 gI(-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 (del P), remediation efficiency and surfactant consumption were investigated. Even for low injection velocities (4 x 10(-4) ms(-1)), capillary numbers were high enough (similar to 8 x 10(-3)) to push the DNAPL efficiently. DNAPL lowered del P for foam propagation because of its destabilising effect. The use of CO2 as gas reduced the del Ps for foam propagation by 35%. del 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. (C) 2015 Elsevier B.V. All rights reserved.