Methanogenic Biotransformation of Chlorinated Hydrocarbons in Ground Water

Abstract

Chlorinated hydrocarbons enter aquifers by various ways. Bacteria found in ground water transform the dissolved compounds into one or more intermediate compounds, then into a final compound that is sometimes not biodegradable. Biotransformation of tetrachloroefhylene (PCE) to trichloroethylene (TCE), dichloroethylene (DCE), and vinyl chloride (VC) by a reductive dehalogenation process catalyzed by microorganisms has been observed in aquifers and laboratory columns under methanogenic conditions. The pathway for conversion includes the replacement of a chlorine atom by a hydrogen atom. The quantification of these conversion and migration processes of parent and intermediate compounds is achieved by mole balance equations of respective compounds, Michaelis‐Menten kinetic equations, and stoichiometric relations. Following a simplification of the general model for a column experiment, a numerical solution is obtained by using a finite difference scheme to provide estimates of mole fractions of parent and intermediate compounds. The numerical results show a favorable match with experimental data. A significant sensitivity to model parameters, particularly the rate constants of parent compounds, is discovered. It is concluded that biotransformation processes can be satisfactorily quantified by first‐order rate expressions.