Electrochemically-assisted thermal-based technologies for soil remediation

Abstract

In situ thermal remediation (ISTR) technologies are considered a good option to both, evaporate volatile organic contaminants (VOCs) and enhance the mass transport of dissolved chemicals, avoiding the drawbacks associated with soil excavation. Subsurface heating can be promoted by using direct current (DC) or alternating current (AC), thanks to the Joule effect that arises when electricity is converted into heat as it flows through a low conductivity medium like soil. In this chapter, after a short introduction about existing ISTR technologies, electrochemical ISTR (i.e., electrothermal methods), is reviewed with detail. The fundamentals, mathematical considerations, and modelling are described, thereby presenting some examples that clearly reveal the temperature dependence of key physical properties of soil and water, as well as the scale effect. Several companies that have successfully scaled-up the DC and AC electrothermal techniques are mentioned throughout the chapter. A key idea to keep in mind is that the lowest effective temperature should be the one chosen in ISTR to avoid collateral effects like excessive energy consumption and negative effects on soil properties, including loss of fertility. Coupling of electrical heating with simultaneous in situ chemical oxidation (ISCO) via generation of highly oxidizing species like sulfate radicals enables the operation at milder temperature, thus reducing the electrical power consumption and allowing the degradation of pollutants in addition to their desorption/volatilization.