SOLVENT WASHING OF PCP CONTAMINATED SOILS WITH ANAEROBIC TREATMENT OF WASH FLUIDS

A solvent washing procedure for the removal of pentachlorophenol (PCP) from contaminated soils is presented. This procedure can be used in both in-situ and above-ground soil washing applications. The in-situ solvent washing (flushing) of soil was simulated by continuously flushing solvent through a packed bed of soil until the effluent PCP concentrations decrease to below the detection limit. The above-ground (ex-situ) soil washing was simulated by batch tests (reverse isotherms) conducted on PCP contaminated soil. Acetone was found to be less effective than ethanol in flushing PCP from contaminated soil. Soil solvent flushing was evaluated for 20 X 40, 60 X 80, and 100 X 140 U.S. Mesh size soil fractions loaded with 100 ppm of PCP. The flushing solvent, 95% ethanol, was applied at three different flow rates. Lower solvent flow rates were more effective, for the same solvent throughput, than higher flow rates in extracting PCP thus suggesting that desorption kinetics was rate limiting. The 20 X 40 U.S. Mesh soil was flushed with various ethanol and water mixtures; the 75% ethanol solution removed more PCP than other mixtures. Batch extraction tests, conducted on 20 X 40, 100 X 140 U.S. Mesh size soil and the clay fraction of the same soil, revealed that 50% and 75% ethanol and water solutions consistently removed the highest amounts of PCP. The wash fluids were fed to an expanded-bed anaerobic granular activated carbon (GAC) bioreactor, where the PCP content of the wash fluid was biodegraded and the ethanol served as the primary substrate.