Complete degradation of tetrachloroethene in coupled anoxic and oxic chemostats.
Anaerobic tetrachloroethene (C2Cl4)-dechlorinating bacteria were enriched in slurries from chloroethene-contaminated soil. With methanol as electron donor, C2Cl4 and trichloroethene (C2HCl3) were reductively dechlorinated to cis-1,2-dichloroethene (cis-C2H2Cl2), whereas, with L-lactate or formate, complete dechlorination of C2Cl4 via C2HCl3, cis-C2H2Cl2 and chloroethene (C2H3Cl) to ethene was obtained. In oxic soil slurries with methane as a substrate, complete co-metabolic degradation of cis-C2H2Cl2 was obtained, whereas C2HCl3 was partially degraded. With toluene or phenol both of the above were readily co-metabolized. Complete degradation of C2Cl4 was obtained in sequentially coupled anoxic and oxic chemostats, which were inoculated with the slurry enrichments. Apparent steady states were obtained at various dilution rates (0.02-0.4 h-1) and influent C2Cl4-concentrations (100-1000 microM). In anoxic chemostats with a mixture of formate and glucose as the carbon and electron source, C2Cl4 was transformed at high rates (above 140 micromol 1-1 h-1, corresponding to 145 nmol Cl- min-1 mg protein-1), into cis-C2H2Cl2 and C2H3Cl. Reductive dechlorination was not affected by addition of 5 mM sulphate, but strongly inhibited after addition of 5 mM nitrate. Our results (high specific dechlorination rates and loss of dechlorination capacity in the absence of C2Cl4) suggest that C2Cl4-dechlorination in the anoxic chemostat was catalysed by specialized dechlorinating bacteria. The partially dechlorinated intermediates, cis-C2H2Cl2 and C2H3Cl, were further degraded by aerobic phenol-metaboizing bacteria. The maximum capacity for chloroethene (the sum of tri-, di- and monochloro derivatives removed) degradation in the oxic chemostat was 95 micromol 1-1 h-1 (20 nmol min-1 mg protein-1), and that of the combined anoxic --> oxic reactor system was 43.4 micromol 1-1 h-1. This is significantly higher than reported thus far.
Gerritse
J
J
Department of Microbiology, University of Groningen, The Netherlands. j.gerritse@biol.rug.nl
Kloetstra
G
G
Borger
A
A
Dalstra
G
G
Alphenaar
A
A
Gottschal
J C
JC
D001420:Bacteria, Aerobic / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D001421:Bacteria, Anaerobic / Q000302:isolation & purification / Q000378:metabolism*; D001673:Biodegradation, Environmental; D019149:Bioreactors; D004785:Environmental Pollutants / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000378:metabolism; D019800:Phenol / Q000494:pharmacology; D012988:Soil Microbiology; D013696:Temperature; D013750:Tetrachloroethylene / Q000378:metabolism*; D014241:Trichloroethylene / Q000378:metabolism
D004785:Environmental Pollutants; D014241:Trichloroethylene; D019800:Phenol; D010100:Oxygen; D013750:Tetrachloroethylene