Reduction of Contaminants in Soil and Water By Direct Electric Current - Electrokinetics for Petroleum and Environmental Engineers - page 34

used successfully to transport reactive agents, such as nano-particle slur-
ries to enhance in-situ reactions that convert contaminants, or chelating
or surfactant agents to solubilize the contaminants so they can be trans-
ported with water advection. More recently, evidence was provided that
shows how direct electric current can contribute to success of the desired
transformation reactions by not only providing the “driving force” nec-
essary to deliver active reagents, but also by lowering the energy for the
redox reactions to occur. This enhancement of transformation reactions
was attributed to the double-layer polarization of the clay surfaces leading
to Faradaic processes under the applied electric field.
In most field situations, the contaminants are found adsorbed onto
soil surfaces, iron-oxide coatings, soil colloids and natural organic mat-
ter. Most contaminants are retained in clay interstices as hydroxycar-
bonate complexes, or present in the form of immobile precipitates and
products in soil pore throats and pore-pockets that “lace” the vadose
zone. This exacerbates clean-up efforts as the available technologies, such
as in-situ bioremediation, chemical treatment or the traditional pump-
and-treat method may not be able to treat the entire site effectively in low
permeability soils. Electrokinetics treatment, when designed to properly
address the site specific features, can potentially reduce the subsurface pol-
lution by transporting and/or transforming contaminants, and enhance
resource recovery by extracting trapped materials (i.e., heavy metals, oils
and petroleum) which may not be extractable by other means. This chapter
first provides an overview of the use of direct electric current for envi-
ronmental mitigation in the subsurface, and discusses with examples the
application of direct electric current to:

i. transport of environmental contaminants for the purpose of
extracting them out of subsurface soil and water;
ii. transfer of environmental contaminants for the purpose of
their destruction in-situ or conversion to environmentally
less toxic/benign compounds; and
iii. recover resource by extraction and accumulation of usable
materials from subsurface soil and water.

2.2 Overview of Direct Electric Current in Subsurface

Environmental Mitigation

Electrically induced migration of ions and water is a proven method of
externally forced mass transport in clay soils for contaminant remediation