Kinetics of DCE and VC mineralization under methanogenic and Fe(III)-reducing conditions

The kinetics of anaerobic mineralization of DCE and VC under methanogenic and Fe(III)-reducing conditions as a function of dissolved contaminant concentration were evaluated. Microorganisms indigenous to creek bed sediments, where groundwater contaminated with chlorinated ethenes continuously discharges, demonstrated significant mineralization of DCE and VC under methanogenic and Fe(III)-reducing conditions. Over 37 days,the recovery of [1,2-C-14]VC radioactivity as (CO2)-C-14 ranged from 5% to 44% and from 8% to 100% under methanogenic and Fe(III)-reducing conditions, respectively. The recovery of [1,2-C-14]DCE radioactivity as (CO2)-C-14 ranged from 4% to 14% and did not vary significantly between methanogenic and Fe(III)-reducing conditions. VC mineralization was described by Michaelis-Menten kinetics. Under methanogenic conditions, V-max was 0.19 +/- 0.01 mu mol L-1 d(-1) and the half-saturation constant, k(m), was 7.6 +/- 1.7 mu M. Under Fe(III)-reducing conditions, V-max was 0.76 +/- 0.07 mu mol L-1 d(-1) and k(m) was 1.3 +/- 0.5 mu M. In contrast, DCE mineralization could be described by first-order kinetics. The first-order degradation rate constant for DCE mineralization was 0.6 +/- 0.2% d(-1) under methanogenic and Fe(III)-reducing conditions. The results indicate that the kinetics of chlorinated ethene mineralization can vary significantly with the specific contaminant and the predominant redox conditions under which mineralization occurs.