Electrobioremediation: Combined Electrokinetics and Bioremediation Technology for Contaminated Site Remediation

Bioremediation of contaminated sites uses the capacity of soil microorganisms to remove, degrade or immobilize the contaminants in soils and groundwater. Organic contaminants can be degraded to simpler molecules or even completely metabolized under aerobic (final products: CO2 and H2O) or anaerobic (final products: CH4 and CO2) conditions. Soil microorganisms consume organic contaminants as a substrate for their metabolism that can be enhanced with the appropriate conditions such as pH, temperature, oxygen, nutrients and electron donors or acceptors. Inorganic anions, such as nitrate and phosphate, are consumed by the microorganisms as necessary nutrients for their metabolism. Other inorganic anions (e.g., sulfate) and heavy metals are not metabolized, but they can be transformed to less bioavailable species reducing their biotoxicity, the exposure to living organisms and the possibility of entering the trophic chain. The main limitations of bioremediation in both in situ and ex situ applications are related to the biological activity and the conditions to enhance the metabolism of soil microflora: pH, temperature, moisture, oxygen, nutrients and electron acceptors/donors. These limitations can be overcome with the simultaneous application of an electric field in the contaminated site. This coupled technology is often called electrobioremediation. The electric field and the electrokinetic transport can be used to supply nutrients, oxygen and any other substance that may enhance the microbial activity in the soils. The electrochemical reactions upon the electrodes may supply the soils with the necessary electron acceptors/donors for the metabolic reactions. The electric field may also favor the mobilization and transport of contaminants and bacteria, increasing the bioavailability of the contaminants and therefore the degradation rate. The success of electrobioremediation depends on the proper application of the electric field to achieve the appropriate environmental conditions to enhance the metabolic activity of the soil microflora, avoiding significant changes in the physicochemical characteristic of soil that may compromise the survival of the microorganisms. The main variables that affect electrobioremediation are: voltage, electric current intensity, type of current (AC/DC), mode of operation (continuous, periodic, polarity inversion), electrode material and stability, addition of nutrients and the use of other facilitating agents.

Automated summary

Bioremediation utilizes soil microorganisms to remove, degrade or immobilize contaminants. Organic contaminants can be degraded aerobically or anaerobically. Inorganic contaminants can be transformed to less bioavailable species. Electrobioremediation enhances microbial activity through the application of an electric field.