Comparison of Alternative Hydrogen Donors for Anaerobic Reductive Dechlorination of Tetrachloroethene
Final rept. Aug 93-Jan 98
CORNELL UNIV ITHACA NY DEPT OF CIVIL AND ENVIRONMENTAL ENGINEERING
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Selective delivery of H2 to a tetrachloroethene PCE dechlorinator was investigated 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.
- Organic Chemistry
- Physical Chemistry