| Finding environmentally friendly and cost-effective methods to remediate soils contaminated with polycyclic aromatic hydrocarbons (PAHs) is currently one of major concerns of researchers. In this study, a series of small-scale batch and semi-continuous extractions—with and without in situ wet oxidation—were performed on soils polluted with PAHs, using subcritical water (i.e., liquid water at high temperatures and pressures, but below the critical point) as the removal agent. Two types of soil were used: one spiked with four PAHs, and an aged sample. Experiments were performed in a 300-mL reactor. In batch experiments on spiked soils, the following effects were studied: (1) the effect of hot water in the extraction of four PAHs at various temperatures and, (2) the effect of three oxidizing agents (air, oxygen, and hydrogen peroxide) on the PAH content of soil and water after each experiment. A similar study was done on the aged soil using only gaseous oxygen and hydrogen peroxide as oxidizing agents and only at 250°C. Removal of PAHs from spiked soil in the extraction-only experiments was from 79 to 99+%, depending on the molecular weight of the PAR This removal was above 99.1% in the combined extraction and oxidation. Although 28–100% of extracted PAHs were found in the water phase in the extraction-only case, this reduces to a maximum of 10% if the extraction is combined with oxidation. With batch experiments on aged soil, comparable results were obtained.; To find the desorption isotherms and oxidation reaction rates, semi-continuous experiments with residence times of 1 and 2 h were done using aged soil at 250°C and hydrogen peroxide as oxidizing agent. In all combined extraction and oxidation flow experiments, residue PAHs in the remaining soil after the experiments were almost undetectable. In the liquid phase too, in combined extraction and oxidation after first 30 min of the experiments, almost no PAHs could be found.; Based on these results, extraction with hot water, if combined with oxidation, should reduce the cost of remediation and can be used as a feasible alternative technique for remediating contaminated soils and sediments. |
