From: Public Services and Procurement Canada
In situ electro-oxidation consists of applying an electrical field in the soil in order to oxidize contaminants present in both soil and groundwater. The application of an electric current allows, among other things, to partially transform (reduction of toxicity) or to completely decompose the contaminants by oxidation processes. This technology is at the demonstration stage only.
This remediation technique is particularly effective in low permeable saturated soils containing contaminants strongly adsorbed to soil particles.
Electro-oxidation is implemented by the direct application of a low-voltage electric current (energy from 0.2 to 1.5 kWh/tones of soil) using electrodes of about 10 cm in diameter driven into the ground at depths varying between 0.5 and 2.0 m.
Different configurations can be used for an in situ application of the technology. The electrodes can be arranged vertically or horizontally directly in the ground. Generally, the anodes and cathodes are spaced a few metres apart. The electrodes can be designed with different materials such as platinum, lead dioxide (PbO2), diamond doped with boron or titanium compounds. However, less expensive materials such as stainless steel or carbon are generally used.
The implementation of this in situ technology can include:
Other amenities or treatment systems may be required depending on the complementary technology that will be implemented for the recovery or treatment of soil or groundwater. These arrangements are specified in the Fact sheets associated with each technology.
Other materials or storage may be required on site depending on the additional technologies that will be implemented for the treatment of soil and groundwater.
Electro-oxidation causes many redox reactions which can lead to the formation of certain undesirable by-products such as the formation of hydrogen fluoride, chlorine gas, bromate, perchlorate or adsorbable organic halides, but also of strong acids or bases around the electrodes. Installation of a recovery and treatment system for these by-products may be necessary.
In most cases, recovery of the contaminants is not necessary. These are mineralized or considerably altered to no longer pose a risk to the environment.
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.
Small-scale trials (laboratory / pilot) to verify the efficiency of the technology and to determine the number of pairs of electrodes required, their positioning, etc. is recommended due to the state of development of the technology (demonstration).
The presence of conductive or insulating elements which can affect the electrical conductivity of the ground (pipe, building, fence, etc.) must be verified before the application of this technology.
Considering the risk of frost and the temperature conditions in northern environments and since this rehabilitation technology requires high energy consumption, significant mobilization and the work windows being relatively short, it is not well suited to northern and remote areas.
This technology has potential for specific application to certain emerging contaminants such as perfluoroalkyl substances and endocrine disruptors.
This technology induces significant geochemical changes in soil and groundwater (acidification and basification near the electrodes, formation of by-products). The return to the initial conditions must be followed up by groundwater quality monitoring campaigns and one or more soil characterization campaigns.
Depending on the contaminants treated, certain undesirable by-products can be formed. It is important to learn about the different by-products linked to the degradation of certain contaminants to effectively treat the affected matrix.
In addition, heavy metals can precipitate prematurely in soil near the electrodes. Therefore, this soil may need to be removed and treated, if required. Finally, the soil at the periphery of the electrodes can be affected by the increase in pH and will therefore potentially have to be treated.
Electro-oxidation can be combined with other technologies to optimize rehabilitation. For example:
A system for cleaning 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:
This technique is effective in environments with fine soils (clay, silt, clay silt) with high adsorption capacity where few restoration technologies are effective. It applies to both organic and inorganic contaminants. It allows to simultaneously treat several metals as well as a wide variety of organic contaminants.
In Europe and the United States, relatively large-scale projects have already been carried out. For example, the application of this technology to treat mercury in the soil has produced convincing results. Indeed, tests at the Union Canal in Scotland, where an average concentration of total mercury of 243 mg/kg was present in silts, showed a reduction in concentrations of 124 mg/kg after 12 days of treatment.
Main Exposure Mechanisms
Applies or Does Not apply
Monitoring and Mitigation
Dust
Does not 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 vapor 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
Estimation of the potential for steam emissions and emissions monitoring (choice of parameters, types of samples and intervention levels depending on source, risk and local requirements) to confirm predictions
Runoff
Groundwater - displacement
Applies in the case of groundwater treatment
Modeling and monitoring using pressure sensors.
Groundwater - chemical/ geochemical mobilization
Geochemistry modeling, laboratory test and/or pilot tests.
Groundwater quality monitoring
Groundwater - by-product
Estimation of potential by-products and groundwater quality monitoring
Accident/Failure - damage to public services
Records checks and pre-excavation permits, development of excavation or drilling procedures and emergency response[ST7]
Accident/Failure - leak or spill
Accident/Failure – fire or explosion (inflammable vapours)
Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.
Other - Handling contaminated soils or other Solids
Composed by : Maïté Faubert, M.Sc., Nathalie Arel ing. M.Sc., Valérie Léveillé ing., M.Sc.A., PhD, et Christian Gosselin ing., M.Sc., Golder Associés Ltd
Latest update provided by : Maïté Faubert, M.Sc., Nathalie Arel ing. M.Sc., Valérie Léveillé ing., M.Sc.A., PhD, et Christian Gosselin ing., M.Sc., Golder Associés Ltd
Updated Date : December 1, 2021
