Fundamentals of electrokinetics - In-Situ Remediation of Arsenic-Contaminated Sites - page 85

CHAPTER 5

Fundamentals of electrokinetics

Soon-Oh Kim, Keun-Young Lee & Kyoung-Woong Kim

5.1 INTRODUCTION

Numerous sites are contaminated due to various activities such as improper treatment of wastes,
abandoned mining wastes, leakage of landfill leachate, military activities, impertinent collec-
tion of used batteries, and accidental spills. Contamination frequently affects large areas of soil
underlying the surface, and contaminants found in these areas include a wide range of toxic
chemicals such as heavy metals, metalloids, radionuclides, and organic compounds. In addition,
there are various types of contaminated lands such as paddy soils, farmlands, factory sites, mine
fields, and residential districts. Toxic contaminants within and migrating from these lands threaten
human health through their detrimental effects on agricultural crops and drinking water reser-
voirs, including groundwater and surface water in the local area. Accordingly, the remediation
of contaminated sites has become a great environmental concern and urgent priority. Develop-
ment of high-performance technologies for cleaning up these sites is one of the most important
technological challenges.
Until recently, a variety of technologies have been developed to remediate soils, sediments, and
groundwater, and they can generally be classified into three groups based on the principles applied.
The first one is biological remediation, which has been mainly used to detoxify contaminants, par-
ticularly organic toxicants. The technology includes phytoremediation, bioventing/biosparging,
biopile, landfarming, composting, biofilter, and in-situ bioremediation. The second group is
physico-chemical decontamination, which has been usually applied to remove inorganic contam-
inants, especially heavy metals. This includes excavation, soil washing/flushing, solidification
and stabilization (SS), soil vapor extraction (SVE), and electrokinetics. The third decontamination
method is based on thermal principles and includes incineration, thermal desorption, vitrification,
and thermally enhanced SVE.
Even though a number of remediation technologies have been developed so far, most of them
are costly, energy intensive, ineffective, and could cause adverse and secondary environmental
impacts. A major limitation to most successful remediation technologies, such as SVE and soil
washing/flushing, is that they are restricted to soils with high hydraulic conductivity. In other
words, they cannot be effectively used to clean up low-permeability and fine-grained soils and
sediments. Furthermore, most of the technologies have been demonstrated to be inadequate for
remediation of soils affected by a mixture of contaminants, such as heavy metals coexisting
with organic contaminants. In contrast, electrokinetics has been recognized as one of the most
promising technologies to overcome such limitations and difficulties.
Electrokinetics is also termed electrokinetic soil processing, electrokinetic remediation,
electroreclamation, electrochemical remediation, and electrochemical decontamination. The elec-
trokinetics needs low-level current, which is normally direct electricity, except for some special
applications, in order of mA cm − 2 of a cross-sectional area between the electrodes to remove con-
taminants from soils. The low-level direct current results in physico-chemical and hydrological
changes in the soil mass, leading to species transport by coupled mechanisms.
The electrokinetics is an effective technology for removing contaminants in low-permeability
soils ranging from clay to clayey sand. The advantages of this technology include its low cost of

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