Fundamentals of electrokinetics - In-Situ Remediation of Arsenic-Contaminated Sites - page 104

contaminants in soils are crucial in electrokinetic remediation, as discussed in Section 5.3.1.2,
researchers have investigated their speciations using sequential extraction or selective leaching
techniques prior to applying the electrokinetic process. In addition, the stability of residual con-
taminants in soil has been assessed after electrokinetic remediation. Based on the results of the
lab- or bench-scale feasibility studies presented so far, the electrokinetics has been established
as a promising technology for remediation of soils, especially fine-grained ones in which other
remediating technologies, such as soil washing, have failed.
The first field-scale application of electrokinetic soil remediation was carried out by
Geokinetics in 1987 (Lageman, 1993). Subsequently, a number of field works have been per-
formed by many researchers and companies, focusing on the practical field-scale implementation
of electrokinetic remediation of soils contaminated with inorganics such as heavy metals. The
field-scale feasibility study of electrokinetic remediation by Banerjee et al . (1989), undertaken
at a Superfund site at Corvallis, Oregon, was one among the other early field-scale studies
(Oonnittan et al ., 2009). Table 5.5 summarizes the field-scale projects of electrokinetic reme-
diation undertaken to date. Field-scale electrokinetic remediation can be usually implemented
by the application of low-level direct current (DC) between electrodes placed in a contaminated
area. A variety of conditions and parameters of the process should be optimized prior to field
works through laboratory tests, numerical methods, and/or design procedures. The processes
adopted at each site differ in one or more aspects. Basically, two approaches are defined depend-
ing on the type of contaminant (Oonnittan et al ., 2009). The first approach is enhanced removal
in which the contaminants are transported by electromigration and/or by electroosmosis toward
the electrodes for subsequent removal. This approach is applicable for the removal of inorganic
contaminants such as heavy metals. The second approach is treatment without removal, which
involves the electroosmotic transport of contaminants through the treatment zones and may also
include the frequent reversal of polarity of electrodes to control the direction of contaminant
movement. This approach was developed for the removal of organic contaminants from soils
(USEPA, 1997). Although there have been some major hindrances during field operations under-
taken so far, some of the projects shown in Table 5.5 were able to meet their remediation goals.
Results of the field implementations demonstrate that electrokinetics is a promising technology
for the effective remediation of soils contaminated by various contaminants. Nevertheless, the
field applications that have been undertaken reveal there are several factors, such as soil het-
erogeneities, remediation time, formation of by-products, and soil saturation that limit or affect
the overall performance of the technology in the field. In order to improve the effectiveness
of the process, a detailed study of each case is needed to establish the most adequate operat-
ing conditions, including current intensity or electric field strength, electrode deposition, and
chemical conditioning of electrolyte solutions. Recently, several demonstration projects have
been undertaken to remediate various types of sediments. For example, a field study was carried
out for an alternative sediment remediation technology known as electrochemical geo-oxidation
(ECGO) in Duluth, Minnesota, USA, from 2002 to 2007 and in Copenhagen, Denmark in 2006,
for removal of PAHs, PCBs, Hg, and other miscellaneous contaminants from dredged harbor
sediments (Wittle et al ., 2009). In addition, the demonstration of field-scale electrokinetics
coupled with permeable reactive barriers (PRBs) was undertaken at a landfill site to clean up
the groundwater as well as soil contaminated by the uncontrolled release of landfill leachate
(Chung and Lee, 2007). In summary, a number of field-scale projects have demonstrated the
effectiveness of electrokinetic remediation for removal of various types of contaminants from
different media such as soil, sediment, and groundwater. However, the field demonstrations
indicate that detailed study of contaminated sites is prerequisite for the successful application
of the technology. One must consider several basic questions (Lageman and Pool, 2009): What
parameters must be known to calculate the necessary energy and time to reach a certain reme-
diation goal? How are these parameters obtained and what other field information is needed?
What field equipment should be used? Finally, how is an electrokinetic project designed and
operated?