From: Public Services and Procurement Canada
Electrokinetics is a technology that extracts or immobilizes organic and inorganic contaminants from soil, sediment, sludge or groundwater. Electrokinetics requires the application of a low-intensity electric current between pairs of electrodes (anodes and cathodes) located in and around a contaminated area or installed perpendicular to the direction of groundwater flow to create a barrier. The difference in potential between the electrodes creates physicochemical changes in soils or sediments and facilitates the migration of ions and water to the electrodes. Metallic ions, ammonium, and organic compounds with a positive charge migrate towards the cathode, while anions such as chloride, fluoride, nitrates, and negatively charged organic compounds migrate towards the anode. The application mechanisms of electrokinetics include dissolution, precipitation, volatilization, sorption and three principal transport mechanisms, namely electroosmosis, electromigration and electrophoresis.
In the presence of organic contaminants with a low polarity, separation by electrokinetics alone is not very effective. In these cases, chemo-electrokinetic (a chemical compound with a strong polarity such as carboxymethyl-ß-cyclodextrin) is added to the contaminated matrix to enhance the solubility of the hydrophobic organic compounds and the migration towards an electrode according to the variation of electrical potential, and can improve the application of the technology, especially in fine particle enriched soils (clayey or silty soils).
Electrokinetic technology can be combined with the extraction of contaminants. The processes of contaminant extraction may consist of: electro-deposition (formation of a deposit on the surface of a conductive extractor), precipitation near the electrodes, pumping of water near the electrodes, volatilization of contaminants combined with steam extraction or formation of a complex with ion-exchanging resins. When there is no extraction of contaminants, electrokinetics is used to move the contaminants to an in situ treatment zone, located between the pairs of electrodes where another remediation technology is applied.
Electrokinetics causes much oxidation-reduction reactions that can lead to the formation of some undesirable by-products, such as the formation of chlorine in gaseous form, acids, or strong bases at the periphery of the electrodes. The installation of a recovery and treatment system for gaseous effluents may be necessary.
The implementation of this in situ technology may include:
Other installations or systems may be required depending on the additional technology that will be put in place for the recovery or in situ treatment of soils or groundwater. These are specified in the fact sheets associated with each one of these technologies.
Other materials or storage may be required at the site, depending on the complementary technologies that will be put in place for the treatment of soil and groundwater.
Electrokinetics does not allow the destruction of contaminants; it is used to migrate contaminants to an in situ treatment area where another remediation technology can be used. This technology can produce solid (precipitation) and gaseous residues that need to be processed or appropriately disposed.
Notes:
Tests examining the effect of temperature change on hydraulic conductivity and establishing the zone of freezing with a pilot scale tubing system are recommended to properly design the full-scale containment system.
For groundwater treatment, when a system is decommissioned, it is often possible to observe an increase in contaminant concentrations in the groundwater after the system shut down. Concentrations following system shutdown should be monitored to ensure they remain below the applicable criteria.
This technology induces significant geochemical changes in the aquifer (acidification and basification near the electrodes). Return to ambient conditions must be monitored.
Numerous redox reactions can be generated by electrokinetics, which may create noxious gases such as chlorine gas that must be treated. The formation of solid deposits (precipitates) is also possible during this technology, which must be recovered and disposed. Soils near the electrodes should also be removed and disposed since their chemistry is altered by the precipitation process (e.g. pH change). Significant changes in pH around the electrodes can induce the formation and mobilization of secondary products, such as the mobilization of heavy metals.
Electrokinetic technology may be combined with other technologies to optimize remediation. For example:
A system for recovering and treating contaminants that can accumulate around the electrodes may be required, as well as a system for recovering and treating gaseous effluents, if required.
The following websites provide application examples:
Electrokinetic technology, although expensive, is an interesting in situ remediation solution to treat contamination within fine particle soils (clayey and silty soils) where other remediation technologies are not suitable. There have been only a few commercial applications of electrokinetic remediation in North America. However, there have been successful demonstrations of the in situ electrokinetic remediation technology in Europe.
In the state of Wisconsin in the United States, a site consisted of high levels of trichloroethylene and dense non-aqueous phase liquid, with some areas having concentrations higher than 1000 mg/kg. The soil consisted of saturated clay and silt. Remediation was carried out with two anodes and a cathode and monitoring for this site was done remotely, thereby saving some operational costs. The entire project lasted over 2 years, until 2008. Post-treatment sampling showed that more than two thirds of the total trichloroethylene was withdrawn, and the dense non-aqueous phase liquid areas decreased
Main Exposure Mechanisms
Applies or Doesn’t apply
Monitoring and Mitigation
Dust
Doesn't apply
N/A
Atmospheric/Steam Emissions—Point Sources or Chimneys
Applies
Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements])
Atmospheric/Steam Emissions—Non-point Sources
Monitoring of soil vapour migration (choice of parameters, types of samples and type of intervention [depending on source, risk or local requirements]), validation of the presence of potential preferential pathways.
Air/steam—by-products
Doesn’t apply
Runoff
Groundwater—displacement
Groundwater—chemical/ geochemical mobilization
Groundwater—by-product
Accident/Failure—damage to public services
Review existing records and obtain pre-drilling permits, establish special excavation procedures, preparation/practice of emergency interventions.
Accident/Failure—leak or spill
Accident/Failure—fire or explosion (inflammable vapours)
Other—Handling contaminated soils or other Solids
Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions
Composed by : Mahaut Ricciardi-Rigault, M.Sc., MCEBR
Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada
Updated Date : April 23, 2014
Latest update provided by : Nathalie Arel, P.Eng., M.Sc., Christian Gosselin, P.Eng., M.Eng. and Sylvain Hains, P.Eng., M.Sc., Golder Associés Ltée
Updated Date : March 22, 2019
