SUPERCRITICAL FLUID TECHNOLOGY--REMEDIATION OF PCB/PAH CONTAMINATED SOILS

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A Two-stage supercritical fluid technology (SCF) of supercritical extraction (SCE) of polychlorinated biphenyls (PCBs)/chlorinated hydrocarbons from contaminated soil and supercritical water oxidation (SCWO) of the extracted PCBs/chlorinated hydrocarbons has been advanced to remediate contaminated soils and contaminated sediments. The advantages of SCF processes over conventional methods include enhanced solubility of organics, complete oxidation using SCWO, simplicity of separation of pollutants from the solvent stream, reduced energy costs in the processing, and treated soils/sediments free of toxic solvents. Results of the current funding period include the definition of processing conditions to achieve sub 5 ppm residual PCBs (Aroclor 1248) in soils and sediments from initial contamination levels of ca 1,000-4,500 ppm. Preliminary economic analysis indicates this SDCF technology cost of $220- $270/m3 soil processed is economically competitive with other processes advanced. Additionally, fundamental thermodynamic solubility data have been acquired for specific PCB congeners in SC-CO2, and fundamental desorption rate data of Aroclor 1248 for a variety of soils/sediments and contacting conditions. Models developed to describe these data will be useful for process calculations. Work on bench-scale SCE studies (ca 2.0 liter extractor volume) to define the extractor configuration and secure engineering data, and work on SCWO experiments will have only been initiated. The project's specific aims are; (10 Bench-scale studies will define the extractor configuration (soils/sediments -SCF contacting) and determine extractor efficiency using clean soils, Aroclor 1248 spiked soils and actual contaminated materials. Results will be used for mobile Demonstration unit design and refined process economics. Studies will be extended to mixed PCB/PAH contaminated soils. (2) Kinetic experiments will define SCWO conditions for destruction of PCBs and determine kinetic rate data for reactor design. (30 The technology will be extended to mixed organic systems of polycyclic aromatic hydrocarbons (PAHs)/PCBs contaminated soils/sediments. Screening studies will be conducted to determine suitable CO2/modifier systems and operating conditions for efficient extraction. Thermodynamic solubility data, sorption equilibrium coefficient data, and desorption rate data will be acquired and analyzed. Preliminary economic cost analysis will be made, and the results will specify conditions for bench-scale experiments.