Concentration Effects on Chlorinated Aliphatic Transformation Kinetics

Abstract

Studies were conducted to determine how the concentration of a chlorinated aliphatic affects acetate utilization rates and its own transformation in methanogenic systems. In these experiments, the chlorinated aliphatics used were dichloromethane (DCM), chloroform (CF), and 1,1,1-trichloroethane (TCA). Experiments were conducted in batch systems using acetate-enrichment cultures maintained at 20°C. Cultures had been exposed to these chlorinated aliphatics for approximately 2 years prior to these experiments. All three compounds were found to inhibit acetate utilization. DCM was the least inhibitory, CF the most. An uncompetitive inhibition model described DCM and TCA inhibition, with inhibition constants of 8.0 mg/L and 0.5 mg/L, respectively. CF inhibition appears to result from a more complex inhibition mechanism. CF and TCA were also found to be toxic to their own transformation, with CF being more toxic than TCA on a mg/L basis. DCM transformation in batch systems was not observed, despite previous acclimation to DCM.