Kinetic model for the biotransformation of tetrachloroethylene in groundwater

The biotransformation of tetrachloroethylene (PCE) to trichloroethylene (TCE) and then to cis-1,2-dichloroethylene (cis-DCE) under an anaerobic condition was studied using static soil microcosms. The kinetics of the biotransformation could be well approximated by the consecutive first-order reaction model, PCE →k₁ TCE →k₂ cis-DCE

This model implied that the total amount of the above three compounds was always constant and was equal to the initial amount of PCE, even if the amount of each compound changed with time. Based on this stoichiometric relationship, two indices to characterize groundwater contamination with PCE were derived. The first was the total contamination level which was defined by the total molarity of the three compounds. The second was the degradation level which was defined by the total molar percentage of the products (TCE+DCE). These indices enabled us to evaluate the initial molarity of the pollutant PCE and the degree of the degradation. The kinetic theory also provided a useful rule such that the same time-concentration profile was obtained for the same ratio of the kinetic constants k₂/k₁, even if the scale of time changed. This rule enabled us to estimate the ratio of the kinetic constants, which suggested environmental fate of groundwater, from observed molarities of the three compounds.