Soil pollution with petroleum-based fuels is a serious issue causing environmental problems. Recently, the use of plasma technologies for soil remediation has shown an interest and great potential. The remediation process can be performed in a fast timeframe without adding supplementary chemical reagents or without additional pre-treatment of the polluted soil. As a result, the use of plasma enables to obtain highly effective degradation of pollutants. Thus, in the present experimental research, diesel fuel removal from contaminated soil by utilizing thermal water vapor arc plasma was investigated. It was found that increased concentration of diesel fuel in the soil raised carbon and hydrogen concentrations in the soil. Moreover, soil surface morphology was modified by causing the formation of bigger agglomerates. It was also determined that after the plasma treatment process, soil grains became akin in size and structure to clean soil grains. A complete desorption of carbon, which came from diesel fuel to the soil, and a slight decomposition of organic carbon present in the soil were observed during the soil remediation process. Thermogravimetric analysis showed that regardless of the diesel fuel concentration in the soil, four stages of mass loss were observed: moisture loss, vaporization, and combustion of diesel fuel as well as reduction of volatiles and char in the soil. Producer gas analysis indicated that during soil remediation diesel fuel was mainly converted to synthesis gas, i.e., a mixture of H2, CO, and CO2. Moreover, the decomposition of diesel fuel and the formation of synthesis gas depended on the amount of pollutant in the soil. According to the obtained results, thermal water vapor arc plasma was able to completely remove diesel fuel from polluted soil in the form of synthesis gas with no significant influence on soil's properties.
Keywords: Diesel fuel; Hydrocarbons; Soil remediation; Synthesis gas; Thermal plasma; Water vapor.