Substrate interactions during the anaerobic biodegradation of 1,1,1-trichloroethane

Halogenated aliphatic hydrocarbons are used in large amounts, persist when released into the environment, and can have adverse effects on human health. Reductive dehalogenation, in which cleavage of carbon-halogen bonds is accompanied by electron transfer to the halogenated substrate, is the most important mechanism for the anaerobic biodegradation of highly halogenated aliphatic hydrocarbons. The concentrations of primary electron-donor and -acceptor substrates, which control the intracellular availability of electrons, can affect the rates of these reactions. A mechanism-based model that describes the effects of the concentrations of primary electron donors and acceptors on the kinetics of reductive dehalogenation was developed and tested in anaerobic biofilm reactors. 1,1,1-trichloroethane (TCA) was used as a model halogenated substrate. The model is based on the assumption that the rate of reductive dehalogenation is controlled by the intracellular concentration of a reduced metalloenzyme (the dehalogenase). The concentration of the reduced dehalogenase is controlled by the external concentrations of the electron donor and acceptor. Although Monod kinetics adequately described the relationship between TCA concentration and its biodegradation rate, the Monod kinetic parameters were functions of the concentrations of the primary electron donor and acceptor. The apparent maximum specific rate of TCA biodegration, q$\sb{\rm m,ap}$, and the apparent half-saturation concentration, K$\sb{\rm ap}$, increased as the concentration of the electron-donor substrate increased. The primary electron-acceptor substrate slowed the first-order rate of TCA biodegradation, because it caused K$\sb{\rm ap}$ to increase without affecting q$\sb{\rm m,ap}$. These results provide a quantitative and mechanistically based tool for understanding and controlling the rates of reductive dehalogenation in treatment reactors and in situ bioremediations.U of I OnlyETDs are only available to UIUC Users without author permissio