Chlorinated ethene half-velocity coefficients (K-s) for reductive dehalogenation

Biological reduction of the chlorinated solvents tetrachloroethene (PCE) an d trichloroethene (TCE) completely to ethene is of interest for engineered or intrinsic destruction of these prevalent groundwater contaminants. Howev er, the transformations are frequently not complete, leading to the product ion of vinyl chloride (VC), a more hazardous compound. Factors affecting th e relative rates of destruction of the solvents and their intermediate prod ucts are thus of interest. The maximum degradation rates (kX) and half-velo city coefficients (Ks) for these chlorinated ethenes used as electron accep ters in reductive dehalogenation with hydrogen in excess were examined usin g an enrichment culture grown on benzoate, hydrogen, and PCE. Initial dehal ogenation rates were measured at various chlorinated ethene concentrations in batch studies. With 38 mg/L volatile suspended solids of this culture, t he kX and 95% confidence intervals for PCE, TCE, cis-dichloroethene (cDCE), and VC at 25 degrees C were found to be 77 +/- 5, 59 +/- 11, 14 +/- 3, and 13 +/- 3 mu M/day with Ks values of 0.11 +/- 0.04, 1.4 +/- 0.9, 3.3 +/- 2. 2, and 2.6 +/- 1.9 mu M, respectively. The lower maximum transformation rat es and higher Ks values for cDCE and VC partly explain why incomplete trans formation of PCE and TCE often occurs in the field.