1.6 Cosolvency and Alcohol Flushing

 It has been demonstrated that adding a cosolvent to an oil-water system will increase the

aqueous solubility of the oil [Nkedi-Kizza et al., 1987; Banerjee and Yalkowsky, 1988]. An

alcohol will decrease the polarity of the water, allowing the nonpolar organic compound to

dissolve more readily [Augustijn et al., 1997]. The relationship of the cosolvent in the aqueous

phase to the solubility of the hydrophobic compound was described by Rao et al. [1990].

 log S...x =log S, +A- .C-, fc (1-2)

The log of the solubility of component i in the cosolvent-water mixture (Smx) is equal to the

sum of the log of the aqueous solubility of i (Sw) and the product of the water-cosolvent

interaction (/, ), the cosolvency power of the solvent for i (a,), and the volume fraction of

cosolvent (fe). For most completely miscible organic solvents (CMOS), / = 1.0.

 The cosolvency power (o-a) is defined by Eq.1-3, where S, is the solubility ofi in pure

cosolvent [Rao et al., 1990].


 C, = log S (1-3)


This is the most important parameter in cosolvency theory. There is a well validated linear

relationship between the interfacial free energy of the cosolvent and the molecular surface area

of the hydrophobic organic compound [Banerjee and Yalkowsky, 1988]. Thus, the solubility of

solute i increases with decreasing solvent polarity.

 Due to costs and duration for conventional pump-and-treat systems for plume control at

DNAPL sites, enhanced dissolution techniques are desirable. One of these methods is cosolvent

flushing, in particular using alcohols as the solubility enhancement agent. This has been called a

variety of terms like cosolvent flooding, enhanced pump-and-treatment, enhanced dissolution,