Modelling of in situ microwave heating of hydrocarbon-polluted soils: Influence of soil properties and operating conditions on electric field variation and temperature profiles

The limits of microwave (MW) heating in situ application for the remediation of hydrocarbon-polluted soils have been investigated by means of a dedicated simulating model. A computer code was expressly developed and applied to simulate the physical phenomena induced by a MW treatment. MW process was modelled by means of the mono-dimensional transient equations of energy, taking into account the interaction between the electromagnetic field and soil and conductivity phenomena. The model was validated by comparison with experimental results from lab-scale activities. Simulations investigated the influence of soil texture and moisture and operating conditions on electric field penetration into the soil and inducted soil temperature profiles. Main results indicate that all investigated parameters significantly influenced the effectiveness of the heating process. In generally, the sandy soil appeared to be more penetrable by MWs respect to the clayey one and higher electric field and soil temperature values were found for the sandy soil with the lower water content. Results also revealed that, for the successful remediation of a clayey soil, a maximum distance of 76 cm should be considered when applying an incident electric field of 1000 V m(-1) for 15 days, whereas a higher distance of 101 cm can be taken in consideration in the case of sandy soil. A further slight distance increase can be achievable in the case of lowest-moisture soil (5%). Overall, the general performance of the treatment can be greatly improved by increasing the incident electric field to a value 1500 V m(-1). In this case, a 15-day heating of a sandy soil led to the maximum distance calculated of 145 cm. Obtained results are of scientific and practical interest and represent the basis for further technical, energy and economic studies, useful to better define the limits of the in situ MW treatment real applicability. The proposed model, giving good prediction of the experimental data for electric field and soil temperature variation, represents a powerful and suitable tool to predict the impact of operating conditions on the effectiveness of the MW techniques. (C) 2016 Elsevier B.V. All rights reserved.