ELECTROKINETIC DECONTAMINATION UNITS

Description

Electrokinetic decontamination is a relatively new technology for the removal of metals and other inorganic pollutants from contaminated soil. Arrays of electrodes are used to produce an electrical field across contaminated soil. The electrodes and their housings are inserted into the ground to the required depth. The electric field forces the charged particles to migrate towards the electrode of opposite polarity; for example, positively-charged heavy metal ions move to the negatively-charged cathode. The anodes and cathodes can be integrated into water circulation systems to allow the pollutants to be removed continually from the vicinity of the electrodes. Alternatively, when the concentration of contaminant at an electrode reaches a set limit, a removal process can be triggered. At the surface, lead and copper contamination can be recovered in their metallic forms by an electrolytic cell. Other metals and metalloids, such as arsenic, are usually removed in precipitate form as the hydroxide.

An additional benefit of electrokinetic decontamination is that the electrokinetic processes have the ability to cause the migration and distribution of microorganisms through the soil. This can aid the bioremediation of other contaminant types.

Electrokinetic decontamination can also be carried out after excavation of the soil. The soil can be treated in a temporary remediation deposit or in batches in electrically-isolated containers.

Application

Electrokinetic technology can be used to remove inorganic contaminants such as heavy metals, cyanides, nitrates and phosphates from soil and groundwater. Electrokinetic decontamination can be carried out in situ. Lines of electrodes, known as electrokinetic fences, can be constructed to restrict the movement of pollutants in groundwater. The efficiency of electrokinetic decontamination can be increased significantly through pretreatment of the soil with both acid solutions and biologically degradable complexing agents.

Sizing

The electrical consumption depends upon the type of soil and the type and concentration of contaminants. For a typical in situ project treating about 1000 m3 of contaminated soil, the energy consumption can range from 150 kWh/tonne to 400 kWh/tonne. The time taken to successfully remediate a site will depend on the volume of soil and the type of contaminants. The concentration of arsenic at one site was reduced from 115 mg/kg to about 10 mg/kg in 80 days; another site with about 30 times the volume of soil contaminated with 250 mg/kg of cadmium was remediated within two years. As with other technologies for the treatment of contaminated land, survey and pilot work is essential before commencement.