ANAEROBIC/AEROBIC BIODEGRADATION OF PENTACHLOROPHENOL USING GAC FLUIDIZED BED BIOREACTORS: OPTIMIZATION OF THE EMPTY BED CONTACT TIME
Two bench-scale anaerobic GAC fluidized bed reactors were constructed and operated to study pentachlorophenol (PCP) biodegradation. 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. The introduction of a diesel-containing feed into the anaerobic reactor B had relatively no effect on PCP degradation and no changes in the effluent monochlorophenol concentration were observed. When the influent ethanol was reduced from 1386 to 138.6 mg/l, no effect on PCP degradation was observed. Similar to the diesel feed addition, no immediate effect on PCP biodegradation was observed when the diesel feed was later removed. 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. PCP did not appear in the distillate stream or side product draw at any time in either the synthetic or real spent solvents experiments. Additionally, 85% and 76% of the PCP was recovered in the bottoms for the synthetic and real soil wash solvents experiments. The PCP-laden distillation bottoms were fed to a pilot-scale anaerobic GAC fluidized bed reactor at an influent PCP loading rate of 363.9 (±21.4) mg/l-d and an empty bed contact time of 8.5 hours. The effluent PCP loading was 5.1 (±3.5) g/l-d, representing a PCP reduction of 99.998%.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:pentachlorophenol anaerobic fluidized bed reactors
Date of Publication:01/01/2002