Comparison of Alternative Hydrogen Donors for Anaerobic Reductive Dechlorinationof Tetrachlorothene

摘要

Selective delivery of H2 to a tetrachloroethene (PCE) dechlorinator wasinvestigated and modeled. H2 was delivered using donors lactate, ethanol (EtOH), butyrate, or propionate SUBSTRATES WHOSE FERMENTATION TO H2 is exergonic under H2 partial pressures (ceilings) of less than 1, 0.1, l0 (exp -3.5), and 10 (exp -4.4) atm, respectively. Recent studies of H2 use in reductive dechlorination show that dechlorinators have an affinity for H2 at least an order of magnitude greater than that of hydrogenotrophic methanogens. Slowly fermented substrates producing lower H2 levels may be more effective and persistent selective stimulators of dechlorination than rapidly fermented substrates producing higher H2 levels. Separate, semicontinously operated cultures were enriched with each of the donors. Long-term, all donors equally stimulated the dechlorination of PCE to vinyl chloride and ethene; however, stimulation of methanogenesis differed (EtOH > lactate > butyrate > propionate). During short-term tests, patterns of donor fermentation and H2 production and consumption were significantly different for different donors. When fed amounts stoichiometrically sufficient to completely dechlorinate PCE, half the H2 released during EtOH fermentation was used methanogenically with the remainder channeled to incomplete dechlorination; however, only 1% of the H2 released during propionate fermentation was used methanogenically and the remainder was used for complete dechlorination. A comprehensive model using Michaelis-Menten-type kinetics incorporating H2 thresholds and thermodynamic limitations on donor fermentations was formulated. Mixed-culture behavior under a variety of conditions was fit well by the model.