Hot water extraction with in situ wet oxidation: PAHs removal from soil

We are reporting the results of a small-scale batch extraction with and without in situ wet oxidation of soils polluted with polycyclic aromatic hydrocarbons (PAHs) using subcritical water (liquid water at high temperatures and pressures but below the critical point as the removal agent). Two types of soil; one spiked with four PAHs, and an aged sample were used. Experiments were carried out in a 300 ml volume reactor in the batch mode. In each experiment, the reactor was filled with 45-50 g of soil and 200-220 ml of double distilled water. For extraction without oxidation, the reactor was pressurized with nitrogen, while for those with the oxidation, an oxidizing agent (air, oxygen or hydrogen peroxide) was used. The extraction only experiments were carried out at 230, 250 and 270 degrees C for spiked soil samples, and at 250 degrees C for aged soil samples, while all of the combined extraction and oxidation experiments were carried out at 250 degrees C. Removal of PAHs from spiked soil in extraction-only experiments was from 79 to 99+% depending on the molecular weight of the PAH. This was in the range of 99.1% to excess of 99.99% for the combined extraction and oxidation. While 28-100% of extracted PAHs can be found in water phase in case of extraction alone, this reduces to a maximum of 10% if the extraction is combined with oxidation. With aged soil similar or comparable results were obtained. Based on these results, extraction with hot water, if combined with oxidation, would probably reduce the cost of post treatment for the water and can be used as a feasible alternative technique for remediation of contaminated soils and sediments.