Reduction of Contaminants in Soil and Water By Direct Electric Current - Electrokinetics for Petroleum and Environmental Engineers - page 35

purposes (Pamukcu and Wittle, 1992; Probstein and Hicks, 1993, Lageman,
1993; Acar and Alshawabkeh, 1993, 1996a; Acar et al., 1994; Hicks and
Tondorf 1994; Eykholt and Daniel, 1994; Shapiro et al., 1995; Yeung et
al., 1996; Alshawabkeh and Acar, 1996b; Electorowicz and Boeva, 1996;
Reddy and Parupadi, 1997; Dzenitis, 1997; Chilingar et al., 1997). While
electoosmosis is analogous to soil washing, ion-migration is probably the
primary mechanism of mass transport when the contaminants are ionic or
surface charged. Relative contribution of electroosmosis and ion migra-
tion to the total mass transport varies according to soil type, water con-
tent, ion species, and their concentration. In silts and low-activity clays,
electroosmotic flow reaches maximum in comparison to hydraulic flow.
But the mass transported by ionic migration is always much higher than
the mass transported by electroosmotic advection (Acar and Alshawabkeh,
1993). The effect of electroosmosis decreases significantly when pH and
zeta potential drops in the later stages of a sustained electrokinetic process
under a constant electric potential (Hamed et al., 1991 and Pamukcu et al.,
1997). When micelles (i.e., charged aggregate of molecules or particles) are
formed with other species in the processing fluid, or when slurry masses
are treated, electrophoresis may become significant (Pamukcu et al., 1995).
Chilingar and co-workers (1997) reviewed and evaluated the electro-
bioremediation technologies for remediation of soils contaminated with
hydrocarbons and metals. They found many successful applications of the
combined technologies (Loo et al., 1994) including: (i) primarily passive
biotreatment for degradation of gasoline and diesel in the soil and ground-
water, (ii) combination of biodegradation and electrokinetic transport with
a hot air venting system and ultraviolet light bio-control system for degra-
dation of gasoline in the clayey soil, (iii) closed recovery system consisting
of special enhanced bioremediation for treatment of soil and ground water
for a site contaminated with gasoline.

2.2.1 Theoretical Considerations: Transport of Charged

Species - Electromigration

As in many electrochemical systems, flow of electric current through a
network of a multi-phase material , such as wet soil occurs in different
phases simultaneously: in the bulk liquid (electrolyte in the pores), on the
surface of the solid (clay particles), and in the interface layer(s) between
the solid and the liquid. Flow of the current can be achieved by ionic con-
duction through the liquid phase and electronic conduction through the
solid phase and the interface layer(s). The electronic conduction orthogo-
nal to and along the interface layer(s) takes place via charge transfer. In