Single-stage remediation of contaminated soil-sludge

Contaminated soil containing 3 wt. % hydrocarbons rich in polycyclic aromatic hydrocarbons (PAHS) has been cleaned to environmental acceptable levels by the use of the supercritical water oxidation system. Supercritical water oxidation is an emerging technology that exploits the supercritical properties of water as a reaction medium. A combustion reaction takes place unhindered in the homogeneous supercritical water phase using oxygen or air as an oxidant. Since most organics dissolve readily in supercritical water, the oxidation reaction can proceed at very high kinetic rates. These kinetic rates allow for very short reactor residence times. The accelerated reaction makes supercritical water oxidation an ideal form of treatment for site remediation of hydrocarbon contaminated soil. Experiments conducted on the soil show a twofold beneficiation process, where hazardous material is extracted from the soil and completely destroyed by an oxidation reaction. The resulting bottoms produce a clean soil with a residual hydrocarbon contamination of less than 200 ppm and a top gas stream rich in carbon dioxide and water, thus establishing ''near-zero discharge condition'' of hazardous substances. Preliminary results prove that the process can be very effectively employed as an ultracleaning, ex situ, remediation technology that can readily be implemented on a mobile unit