Microwave heating-mediated remediation of hydrocarbon-polluted soils: Theoretical background and techno-economic considerations

Abstract

Massive amounts of soil and water have been contaminated with hydrocarbon compounds, including fuel and petrochemical products, because of economic and industrial activities. Several chemical-physical or biologic treatments have been studied to remediate hydrocarbon-polluted soils; however, these alternatives may be ineffective, expensive or too lengthy. Otherwise, ex situ conventional thermal desorption was successfully applied to remove organic contaminants, presenting excellent removal values in a very short time but requiring high energy and costs. Microwaves (MW) are a part of the electromagnetic spectrum occurring in the frequency range of 300 MHz-300 GHz, and recently, their application has been identified as a potential tool for hydrocarbon-polluted soil remediation. Compared to other remediation methods, MW heating has advantages including simplicity, safety, flexibility and cost-effectiveness since it offers the potential to significantly reduce treatment times, risk of contamination and costs due to the direct interaction of microwaves with the soil and its ability to overcome heat and mass transfer limitations. In conventional heating systems, the energy is transferred through conduction, convection and radiation, while in MW heating, energy is supplied directly to soil by molecular interaction with the electromagnetic field generated. Therefore, the components of the soil are heated individually and instantaneously, overcoming limits imposed by material heat transfer properties. Literature studies have shown that MW remediation has the potential to remove polar and semipolar organic pollutants from soil. The key factor of the remediation process is represented by the mechanism due to a partial dissipation of the electromagnetic field energy and its conversion into heat, avoiding the limitations of conductive heating phenomena of conventional thermal desorption treatment. This chapter discusses the theoretical background including MW heating process and the related techno-economic features for ex situ full-scale applications in remediation activities of hydrocarbon contaminants.