ELIMINATION OF PCBS BY SUPERCRITICAL EXTRACTION AND WET OXIDATION

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The specific objectives of the proposed research work are to assess the technical feasibility of supercritical extraction (SCE) and supercritical wet oxidation (SCWO) processes to remove and destroy halogenated aromatic hydrocarbons from waste landfill sites. The advantages of supercritical processes over conventional waste treatment methods include enhanced solubility of organics at supercritical conditions, complete oxidation of organics (in the case of SCWO), simplicity of separation of pollutants from the solvent stream, and reduced energy costs in the processing. Further, the treated soil will not be contaminated with any toxic solvent after processing. The effort during the first funding period will have resulted in the design, construction and commission of supercritical extraction and supercritical water oxidation laboratory units. The former operates at 20o to 100 degrees C and 50 atm to 500 atm, and the latter at 100 degrees C to 500 degrees C and 50 atm to 600 atm. This facility has broad capabilities for this research activity permitting acquisition of thermo-dynamic, desorption rate, and kinetic data at these conditions in a safe and hygienic environment. Thermodynamic models to correlate solubility data, screening tests to identify CO2/modifier (methanol, propane, toluene) systems with 2,4,5/2',4',5'-hexachlorobiphenyl/synthetic soil samples, and selected SCWO preliminary feasibility experiments will have been completed. The proposed research focuses on three specific aims. (1) Equilibrium and desorption rate data will be obtained for SCE of Aroclor 1248 using synthetic soil samples and actual PCB contaminated samples. Analysis of data will determine process feasibility and permit preliminary design. (2) Kinetic experiments will be conducted to obtain SCWO rate data of 2,4,5/2',4',5'-hexachlorobiphenyl and extraction liquids from contaminates soils. Data analysis will determine the process feasibility and permit process design estimations. (3) Bench-scale unit experiments will be executed with synthetic and actual soil samples to evaluate and improve the technology. An economic analysis will be conducted for a mobile unit for on-site treatment.