79

BIOTRANSFORMATION OF CARBON TETRACHLORIDE, PERCHLOROETHENE, AND 1,1,1-TRICHLOROETHANE WHEN PRESENT IN MIXTURES

Disappearance of parent compounds and appearance of transformation products are monitored. Biodegradation kinetics are determined using second-order and pseudo-first-order rate expressions ("biomass-corrected"). Rate coefficients for individual compounds fed alone are compared with those when the compound is pre-sent in mixtures.

Methane production and acetate utilization are measured periodically to determine the effects on methanogenesis. Results indicate that the presence of a mixture significantly reduces the rate of degradation of the individual compound. With unacclimated cultures, CT is degraded most rapidly followed by 1,1,1-TCA and PCE.

There is no apparent lag period before the onset of transformation of any of the three compounds. At the concentrations tested, the presence of PCE does not appear to affect the transformation rates of either CT or 1,1,1-TCA. The potential for toxicity effects on biotransformation is being addressed by determining whether the culture possesses a finite capacity for transformation of each of the compounds.

It appears that CT transformation can continue even when measurable transformation of PCE and 1,1,1-TCA has ceased. Results from kinetic experiments are being used to develop a model to describe the effects of mixtures on individual transformation rates. Michaelis-Menten kinetic equations for microbial growth and fortuitous substrate utilization are modified by including terms for toxicity and inhibition. Attempts are also being made to develop acclimated enrichment cultures.

Rate coefficients obtained from the acclimated culture will be compared to those for the unacclimated culture. Understanding the effect of mixtures on transformation is key to developing effective remediation schemes for waters contaminated with mixtures of chlorinated organic compounds.

Key words: anaerobic, bioremediation, mixtures, chlorinated aliphatics