Fundamentals of electrokinetics - In-Situ Remediation of Arsenic-Contaminated Sites - page 94

• Applicability to saturated and unsaturated soils.
• Applicability for heavy metals, metalloids, radionuclides, and organic contaminants, as well
as in any of their combinations (contaminant mixtures or multiple contaminants).
• Feasibility to treat the entire soil mass between the electrodes.
• Effective controlling of the flow of water and contaminants.
• Easy integration with conventional technologies, including barrier and treatment systems.
Even though electrokinetics has been applied due to its discriminative merits, its ability to
achieve remediation goals has yet to be addressed due to major disadvantages such as:
•

Solubilization of major elements in soils and dissolution of mineral constituents of soils.

• Decrease in the efficiencies of electric current as well as contaminant removal due to non-

target chemicals coexisting in soils.

• Post-treatment for land reclamation due to acidification and/or alkalification.

• Precipitation of metal species near the cathode.

• Problems due to electrode corrosion and excess soil heating.

5.3 DESIGN AND OPERATION OF ELECTROKINETIC REMEDIATION

There are a variety of factors and parameters affecting the performance of electrokinetic reme-
diation (Alshawabkeh et al ., 1999; Page and Page, 2002; Virkutyte et al ., 2002). First, the
types and features of soil and contaminants are crucial. The properties of soil evaluated prior
to application of electrokinetic remediation include soil texture, porosity, electric conductivity,
pH and pH buffering capacity, zeta potential of the surface, water content (degree of saturation),
adsorption capacity, organic content, and mineralogy. The characteristics of contaminants tar-
geted are type, concentration (initial level of contamination), ionic mobility, and chemical forms
in soil (Alshawabkeh et al ., 1999). In addition, electrical parameters are important because they
affect electromigration, electroosmosis, and electrolysis of water, and finally control the trans-
port of contaminants. Hence, the overall efficiency and economy of the process are significantly
influenced by electrical parameters. The electrical parameters, which are determined before appli-
cation of electrokinetics, are electric field strength (electrical potential gradient) and current level
(current density) (Kim and Kim, 2002). In order to improve the performance of electrokinetic
remediation, the design of an electrokinetic system should be optimized prior to implementation.
The representative design factors are related to the electrode, electrolyte, enhancement scheme,
and type of electricity. The design of electrodes includes the distance between electrodes with
different polarities (anode-cathode), the spacing of electrodes with equivalent polarity (anode-
anode and cathode-cathode), the configuration (array) of electrodes, and the material and shape
of electrodes (Alshawabkeh et al ., 1999). The pH and composition of electrolyte should be taken
into account. The types of electricity are also important to improve the electrokinetic process.
So far, the direct current (DC) has been usually used in electrokinetic remediation. However, the
alternating current (AC) can be considered depending on the goal of the process (e.g., removal of
volatile organic contaminants through soil heating). Even though the DC electric wave has been
frequently used, in addition, one must evaluate which type of DC electric wave is most suitable
to achieve the most efficient process because a variety of types of DC electric wave (e.g., full-
wave, half-wave, pulse-wave with high frequency) can be generated by using different types of
rectifier. In the next section, the factors affecting the performance of electrokinetic remediation
are briefly discussed along with the parameters considered to optimize the operation and design
of the process.

5.3.1 Factors affecting the performance of electrokinetic remediation
5.3.1.1 Properties of soil
A variety of soil properties affect electrokinetic performance, and they are divided into physical,
chemical, and mineralogical features. The physical properties include texture or particle size