The Electrokinetic Approach
Electroreclamation (ER) is a soil remediation technology that uses electrokinetic effects to remove contamination. It achieves this by applying a difference in potential, thus causing charged particles to migrate to a cathode or anode. Through this technology, heavy metals can be removed from soil with minimal damage to the underlying soil structure.
Electrokinetic remediation can be deployed in four ways:
A network of electrode casings is placed directly in the ground, covering part or the whole of the contaminated area. The distance between electrodes of both equal and opposite charges depends on site specific conditions, but in general this amounts to 1.5 to 2 metres. Contamination is recovered with minimal disturbance to the site. Electrodes can also be placed underneath or inside buildings, either vertically or horizontally.
Batch (ex situ)
In this configuration, contaminated soil is transported to a mobile batch facility or a temporary lagoon and is treated ex situ.
Electrokinetic Fence (EKF)
This uses a chain of electrode pairs deployed in the ground to halt the migration of contaminated groundwater from a point source.
Electrokinetic Biofence (EBF)
Besides the chain of electrodes, a row of ﬁlters with nutrients is placed upstream of the electrodes. Groundwater transports the dissolved nutrients toward the electrodes. Under the inﬂuence of the electrical ﬁeld, the electrically charged nutrients are dispersed homogeneously between the electrodes, enhancing biodegradation
The technology is applicable for diffusely dispersed pollutants both in the nonsaturated and saturated zone and in clay, sand, and peat soils. Contaminants that can be recovered by ER can be heavy metals, arsenic, nitrates, phosphates, halogenides, and polar and/or water – soluble organic compounds such as cyanides, phenols, and nitro aromatics (such as trinitrotoluene [TNT]). Minimal moisture content should be 15% – 20%. The technology is not economically applicable to heavy metals in metallic form, such as metal grindings, slag and cinder, concretions, and paint particles.
Electrokinetic Remediation, however, begins to shine when managing soil that is contaminated with heavy organics, such as weathered fuel oil, mixtures of petroleum-based fluids, diesel oil, and other solvents. The composition of such contamination, together with the adsorption of compounds within the soil, the presence of colloidal suspensions and oil in water and water in oil phases mean that current solitary decontamination methods (such as vacuum extraction and/or pump and treat methods) do not achieve desired results.
A former silver factory in Nieuwpoort, Netherlands, had around 12,500 m3 of soil and groundwater contaminated with volatile organic compounds (VOCs). The intensive phase lasted 2 years, and was applied to 4,800 m3 of soil. This involved AC-heating of soil and groundwater in areas with high concentrations (free product zones and hotspots). Heating was combined with groundwater and soil vapour extraction and periodical injection of nutrients, carbon sources, oxygen and/or electron donors/acceptors.
The extenuate phase lasted 2.5 years, and was applied to 7,700 m3 of soil. During this phase, attention was focused on the biodegradation of in the remaining source areas and adjoining groundwater plumes. This was followed by monitoring and control through periodic sampling and analyses.
Remediation depth was 12m bgs, and target values were reached after 4.5 years, with more than 100 kg of free product removed with minimal damage done to underlying soil structures.