Complete degradation of tetrachloroethene in coupled anoxic and oxic chemostats

Abstract

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.

Characterization of the Corrinoid Iron-Sulfur ProteinTetrachloroethene Reductive Dehalogenase of Dehalobacterrestrictus

“…Desulfitobacterium hafniense strain TCE1 (ϭ DSMZ 12704) was cultivated under anaerobic conditions in a medium described previously (9). The culture was incubated at 30°C and 100 rpm.…”

Reductive Dechlorination of Trichloroethylene (TCE) in Competition with Fe and Mn Oxides—Observed Dynamics in H2-dependent Terminal Electron Accepting Processes

“…This medium composition was previously used by and was originally adapted from Gerritse et al (1997). The inoculum for the batch degradation experiment was grown on 1 mM TCE and 3.5 mM formate at 20 o C in an anaerobic mineral medium containing: 10 μM (NH 4 )H 2 PO 4 , 0.2 mM Na 2 SO 4 , 2.9 mM (NH 4 )HCO 3 , 30 mM 3-(Nmorpholino)propanesulfonic acid (MOPS, pKa = 7.21), 11.9 mM NaOH, 0.1 mM KOH, 1.2 mM Ca(OH) 2 , 0.3 mM MgO, 10 mg L-1 yeast extract, 1 mM cysteine (not included in the experimental medium), 1% resazurin, 1 mL•L -1 trace element stock solution and 1 mL L (Heijthuijsen and Hansen, 1986).…”

Psychrophilic anaerobic treatment of low strength wastewaters

“…On the other hand, a low 0 2 influent concentration resulted in a more or less stable reactor performance even at relative high sucrose loading rates in the first stage (period VI). The significant decrease in the acidifying biomass yield in period VI, might be explained by the fact that facultative and/or aerobic bacteria decrease their growth-yield by a factor 10 under anaerobic conditions (Shen and Guiot, 1996;Gerritse and Gottschal, 1993). In addition, in period VI, a larger fraction of acidifiers might have been strictly anaerobic, characterized by a lower biomass yield.…”