Anaerobic/aerobic biodegradation of pentachlorophenol using GAC fluidized bed bioreactors: Optimization of the empty bed contact time

The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) mandates removal of pentachlorophenol (PCP) contaminated soil with concentrations greater than 1 ppm.; A treatment train was developed to remedy this problem. At the beginning of this train, soil is excavated from the contaminated site and washed with a 50% water/50% ethanol solution in a countercurrent fashion. The washed soil is returned to the site while the soil wash solvent is fed to a distillation column where it is separated into purified ethanol and PCP-laden distillation bottoms. The purified ethanol, is returned to the beginning part of the treatment train to be reused and the PCP-laden distillation bottoms are fed to an anaerobic GAC fluidized bed reactor followed by an aerobic GAC fluidized bed reactor for biological destruction. To define the operating parameters for the anaerobic GAC fluidized bed reactor, two bench-scale anaerobic GAC fluidized bed reactors were constructed. The first reactor (reactor A) was fed a synthetic soil wash solution comprised of 100 mg/l of PCP and 693 mg/l of ethanol while the second reactor (reactor B) was fed 200 mg/l of PCP and 1386 mg/l of ethanol. Over a 3.5 year period, the empty bed contact time was reduced from 9.3 to 1.17 hours in reactor A and from 18.6 to 2.32 hours in reactor B. Results from both reactors showed PCP biodegradation occurred by more than 99.5% during all of the empty bed contact times studied. Initially, PCP was converted to predominately 4-chlorophenol, but switched to 3-chlorophenol over time. At lower empty bed contact times, the 3-chlorophenol began to mineralize in both reactors. A second stage aerobic reactor was added to mineralize the remaining monochlorophenols in the anaerobic effluent stream and their presence in the aerobic effluent stream was never detected. Ethanol was recovered by 97% from the synthetic and real soil wash fluids fed to a distillation column. In the distillate stream, PCP was never detected at any time in any experiment, leaving purified ethanol. PCP also did not appear in the side product draw at any time in either the synthetic or real spent solvents experiments. (Abstract shortened by UMI.)...