This project seeks a safe and economic method for remediating soils and sediments contaminated by polycyclic aromatic hydrocarbons (PAHs), halogenated aromatic hydrocarbons (PCBs), and PCB/PAH mixtures. A two stage supercritical fluid process is proposed. First the PCBs and/or PAHs are desorbed from the soils/sediments by supercritical CO2-co-solvents (SCCO2-CS) on site with a mobile unit. Then the extracted PCBs/PAHs will be oxidatized to mineral products via supercritical water oxidation off site at a central process location.
The project has three major objectives to obtain necessary information towards the above goal. First, solubility studies of PCBs and PAHs in supercritical CO2 with various co-solvents are in progress to identify systems with high solubility for these compounds, temperature and pressure ranges of operation, and capability to extract mixed systems of PCBs and PAHs. Use of single and mixed PCB and PAH species are intended to provide a fundamental research data base.
Second, laboratory scale fixed-bed desorption experiments identify operation conditions to extract PCBs and PAHs from 5000 PPM to sub 10-15 PPM residual concentrations as a function of soil matrix properties and moisture content. A broad database has been obtained for Aroclor 1248 contaminated soils and sediments. Bench scale studies at kilogram sample sizes are in progress to determine extractor configuration for soil/SCCO2-CS contacting, obtain design data, and improve economic analysis of process costs. Aroclor 1248 spiked samples and native contaminated soils (U.S. Naval Base at Bethpage, NY) and sediments (St. Lawrence River and Hudson River) are being evaluated.
Third, supercritical water oxidation studies of PCBs are in progress to determine destruction effiencies, kinetic rate laws, and reaction pathways over a suitable range of operating conditions. Fundamental data will be obtained with single congeners to determine the feasibility of this method to destroy PCBs to harmless by-products.
Efforts are in progress to secure support to test the soil extraction stage of the process using a mobile demonstration unit on a Department of Defense, Department of Energy or Industrial Site. Interest to co-fund and collaborate in this phase has been obtained by the NIEHS technology transfer program and from O'Brien and Gere Engineers, Inc. (OBG), a major environmental remediation firm in Syracuse, NY.
Thermodynamic property data, desorption equilibria and rate data, and the kinetic studies from this project will be of value to other projects in the NIEHS Basic Program. Also, we will present lectures on engineering aspects of hazardous waste cleanup for the proposed program tutorial sessions.
