of a nonionic surfactant and water decreases. For ionic surfactants, the reaction
between the hydrophilic component and water decreases when the salinity of the
system increases (Rosen and Kunjappu 2012).
In general, interfacial tension decreases with increasing temperature (e.g.,
5.5 Â 10
À5 N m
À1 C
À1 for crude oil–water systems), and may be affected by pH,
the addition of surfactants, and other substances in the solution (Schowalter 1979).
The interfacial tension in the DNAPL–water system is directly related to the
capillary pressure through the interface (Mercer and Cohen 1990). The interfacial
tension in a DNAPL–water system varies between zero for completely miscible
liquids, and 72 Â 10
À3 N m
À1 for absolutely immiscible liquids (72 Â 10
À3 N m
À1 is
the water/air surface tension at 25
C) (Lyman et al. 1982).
(2) Mobilizing Residual Contamination
Surfactants are used to reduce the IFT in order to (a) displace maximum pure
products (DNAPLs), and (b) decrease residual saturations.
DNAPLs are displaced when the reduced IFT coupled with the change of
non-wetting phase viscosity overcomes the capillary pressure. Therefore, it becomes
necessary to choose the optimal surfactant concentration which will improve the
recovery yield, and thus reduce residual saturation.
Previous studies have shown that all tested surfactants have the effect of solubilizing and reducing IFT of the TCE–water and PCE–water systems. For TCE,
Aerosol-MA-80 (5 wt%) significantly reduces the IFT of the TCE–water system as
it falls from 35.2 dyn cm
À1 to 0.2 dyn cm
À1 (Dwarakanath et al. 1999). Tween
80 (5 wt%) reduces it from 35.2 dyn cm
À1 to 10.4 dyn cm
À1 (Suchomel et al. 2007).
As for PCE, the Aerosol family of surfactants is very efficient for reducing the
system IFT from 47.8 dyn cm
À1 to less than 0.01 dyn cm
À1 (Dwarakanath et al.
1999; Sabatini et al. 2000; Childs et al. 2004). Triton x-100 and Tween 80 are also
effective (Taylor et al. 2001; Harendra and Vipulanandan 2011).
Field experiments, described in specialized literature, reported recovery yields of
pure chlorinated solvents ranging from 60 to 70% (Rao et al. 1997; Holzmer et al.
2000; Jawitz et al. 2000; Brooks et al. 2004; Soga et al. 2004), or sometimes more
than 90% (Londergan et al. 2001; Abriola et al. 2005; Ramsburg et al. 2005; Pennell
et al. 2014).
2.5.3 Using Surfactant Foam for DNAPL Recovery
Recent laboratory studies on surfactant foam technology for in situ removal of
chlorinated DNAPLs have shown that this technique presents a promising line of
research (Maire et al. 2015, 2016):
• High foam stability for . surfactant at 0.05% was maintained despite presence of
DNAPL
• Strong foams (finely textured foams) resulted in more than 95% DNAPL recovery yield with surfactant consumption below 10 g kg
À1 of DNAPL recovered
• No DNAPL fragmentation or enhanced dissolution (<0.5 g L
À1 ) were observed
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
97
between the hydrophilic component and water decreases when the salinity of the
system increases (Rosen and Kunjappu 2012).
In general, interfacial tension decreases with increasing temperature (e.g.,
5.5 Â 10
À5 N m
À1 C
À1 for crude oil–water systems), and may be affected by pH,
the addition of surfactants, and other substances in the solution (Schowalter 1979).
The interfacial tension in the DNAPL–water system is directly related to the
capillary pressure through the interface (Mercer and Cohen 1990). The interfacial
tension in a DNAPL–water system varies between zero for completely miscible
liquids, and 72 Â 10
À3 N m
À1 for absolutely immiscible liquids (72 Â 10
À3 N m
À1 is
the water/air surface tension at 25
C) (Lyman et al. 1982).
(2) Mobilizing Residual Contamination
Surfactants are used to reduce the IFT in order to (a) displace maximum pure
products (DNAPLs), and (b) decrease residual saturations.
DNAPLs are displaced when the reduced IFT coupled with the change of
non-wetting phase viscosity overcomes the capillary pressure. Therefore, it becomes
necessary to choose the optimal surfactant concentration which will improve the
recovery yield, and thus reduce residual saturation.
Previous studies have shown that all tested surfactants have the effect of solubilizing and reducing IFT of the TCE–water and PCE–water systems. For TCE,
Aerosol-MA-80 (5 wt%) significantly reduces the IFT of the TCE–water system as
it falls from 35.2 dyn cm
À1 to 0.2 dyn cm
À1 (Dwarakanath et al. 1999). Tween
80 (5 wt%) reduces it from 35.2 dyn cm
À1 to 10.4 dyn cm
À1 (Suchomel et al. 2007).
As for PCE, the Aerosol family of surfactants is very efficient for reducing the
system IFT from 47.8 dyn cm
À1 to less than 0.01 dyn cm
À1 (Dwarakanath et al.
1999; Sabatini et al. 2000; Childs et al. 2004). Triton x-100 and Tween 80 are also
effective (Taylor et al. 2001; Harendra and Vipulanandan 2011).
Field experiments, described in specialized literature, reported recovery yields of
pure chlorinated solvents ranging from 60 to 70% (Rao et al. 1997; Holzmer et al.
2000; Jawitz et al. 2000; Brooks et al. 2004; Soga et al. 2004), or sometimes more
than 90% (Londergan et al. 2001; Abriola et al. 2005; Ramsburg et al. 2005; Pennell
et al. 2014).
2.5.3 Using Surfactant Foam for DNAPL Recovery
Recent laboratory studies on surfactant foam technology for in situ removal of
chlorinated DNAPLs have shown that this technique presents a promising line of
research (Maire et al. 2015, 2016):
• High foam stability for . surfactant at 0.05% was maintained despite presence of
DNAPL
• Strong foams (finely textured foams) resulted in more than 95% DNAPL recovery yield with surfactant consumption below 10 g kg
À1 of DNAPL recovered
• No DNAPL fragmentation or enhanced dissolution (<0.5 g L
À1 ) were observed
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
97