PROPANE-INDUCED BIODEGRADATION OF VAPOR-PHASE TRICHLOROETHYLENE

Microbial degradation of trichloroethylene (TCE) has been demonstrated under aerobic conditions with propane. The primary objective of this research was to evaluate the feasibility of introducing a vapor phase form of TCE in the presence of propane to batch bioreactors containing a liquid phase suspension of Mycobacterium vaccae JOB5 to accomplish degradation. The reactor system consisted of th ree phases: a vapor ph ase introducing air, propane, and TCE; a liquid phase of the microbial suspension; and a solid phase in the form of the microorganisms. Long -term and initial rate experiments were conducted on three culture set s to evaluate microbial response. In two long-term tests fed propane a nd approximately 0.1 mg/L and 1 mg/L of TCE, respectively, propane uti lization was more efficient at the high TCE concentration (600 mmol pr opane/mmol TCE versus 11,900 mmol propane/mmol TCE), because the propa ne degradation rate was approximately the same for both tests (6.73 mg /L . h and 7.85 mg/L . h for the high and low tests). In addition, TCE utilization decreased after complete propane consumption. Initial rat e tests on culture sets fed propane only revealed that cells with a hi story of exposure to a high concentration of TCE had the highest speci fic growth rate, but the lowest half-saturation constant (7.60e(-3) h( -1) and 0.10 mg/L, respectively). Tests fed variable TCE concentration s (0.031 to 5.378 mg/L in the liquid phase) with no propane showed TCE depletion but no biomass growth. The tests revealed that the TCE remo val increased as the TCE concentration increased, indicating a greater removal efficiency at the higher concentrations. Tests with a constan t initial propane concentration and variable liquid phase TCE concentr ation revealed that specific propane utilization was essentially the s ame. (C) 1995 John Wiley and Sons, Inc.