Soil electrokinetic remediation (EKR) is an attractive technology [1,2], due to the optimistic
experimental results of extensive laboratory even pilot-scale . This method is designed to remove
contaminants from low permeability soils under the effect of applied current. However, this method
possesses several drawbacks, for example, the EKR will cause soil acidification, but the EKR process
requires an acidic condition during the application, which will promote the release of the heavy metal.
Unfortunately, the condition of soil acidification is unacceptable. Furthermore, electrode configuration
possesses inefficient electrical area, the EKR process is a very time-consuming application and high
energy consumption etc. Obviously, the single EKR technology cannot achieve the best results, but
combining electrokinetic with other remediation methods, promises to obtain more efficient removal
of pollutant, less time and lower energy consumption. The authors objectively review the various
technologies that can be combined with EKR based on these published studies in the last decade and aim
to provide massive references to relative researchers.
Acar, Gale, et al.  described the principles of electrokinetic remediation, direct electric
current was applied to electrodes immersed in water, results in oxidation at the anode and
reduction at the cathode. This is the original EKR, also termed unenhanced electrokinetic
remediation. Electric fields are applied to soil to migrate the charged ions via electrodes placed
into the ground, negative ions move to anode, and positive ions (such as heavy metal ion)
are attracted to cathode. It has been confirmed that the initiates movement of contaminants
by electromigration, electro osmosis, electrolysis and diffusion , and non-ionic species are
transported along with the electroosmotic flow . The key electron transfer reactions that
occur at electrodes during the EKR process is the electrolysis of water:
According to the experiments and pilot-scale studies conducted in the last 10 years, metals such as cadmium , chromium [8-19], copper [20-28], lead [29-35], manganese [36,37], mercury [38,39], nickel , uranium , and zinc , as well as dye [43,44], hydrocarbon[45-54], organochlorines [55-59], polychlorinated biphenyls [60,61], phenols [62,63], chlorophenols , are suitable for electrokinetic remediation and recovery. The author divides those technologies combined with EKR into physical technology, biotechnology and chemical technology, provides the application of these combination-technologies in soil remediation and evaluates these technologies. The most commonly used of these techniques are physical techniques, such as activated bamboo charcoal [65,66], electrode matrix-rotational operation mode , flushing [30,68-71], hexagonal two dimensional [72-74], ion exchange membranes , permeable reaction barrier (e.g. activated charcoal [28,76], Fe(0) [77,78]), pulsed variable electric field [26,79-81], sequential extraction analysis , ultrasonically , upward , washing  and several methods about electrode configuration [11,86, 87]. As for chemical technology, some enhancement methods such as acid enhanced , ammonia enhanced [21,66], iodide-enhanced  and enhanced solution (e.g. complexing agent , chelate agents [90-93], cosolvent , surfactants [51,52,95-97]) are also more commonly used, in addition, there are some other interesting methods such as chemical oxidation [98-101] and zero-valent iron . There are few examples of biotechnology applications, but it is a very promising research direction, including bioleaching , bio stimulation [104,105], microbial pretreatment , phytoremediation , sulfur-oxidizing bacteria . In addition, in order to solve the energy problem, microbial fuel cell  and solar cell [19,27,110-114] are also used in combination with EKR technology for soil remediation.
EKR is very powerful for inducing controlled changes in soil,
however, no single EKR technology that can achieve the best results
but mixing electrokinetic with other technology promises to be the
most effective method so far. Over the past decade, two potential
applications caught our attention. The first is the hexagonal
two-dimensional electrode, which can effectively minimize the
inefficient electrical area. The second is the pulsed variable
electric field, which can effectively minimize energy consumption.
In addition, an interesting idea targets mobile contamination
plumes by development of permeable reaction barrier (PRB).
Throughout the past several decades, the development of EKR
was rapidly, therefore, it is also important to review the studies
and findings so as to estimate the prospect for future researches.
Extensive literatures are reviewed and some of the thoughts on
future development directions of EKR combination-technology are
proposed in this invited paper. This paper aim to provide massive
references to relative researchers, and hope to become a useful
This work was supported by the National Natural Science
Foundation of China (Grant No 41571306), Excellent Youth
Foundation of Hubei Scientific Committee (Grant No 2018CFA067)
and Foundation of Hubei Educational Committee Educational
Commission of Hubei Province of China (Grant No D20181101).
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Professor, Chief Doctor, Director of Department of Pediatric Surgery, Associate Director of Department of Surgery, Doctoral Supervisor Tongji hospital, Tongji medical college, Huazhong University of Science and Technology