Methanotrophic TCE biodegradation in a multistage bioreactor
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Tschantz, MF and Bowman, JP and Donaldson, TL and Bienkowski, PR and Strong-Gunderson, JM and Palumbo, AV and Herbes, SE and Sayler, GS, Methanotrophic TCE biodegradation in a multistage bioreactor, Environmental Science and Technology, 29, (8) pp. 2073-2082. ISSN 0013-936X (1995) [Refereed Article]
A two-stage biorector system was continuously fed a solution of TCE (concentrations ranging between 0.2 and 20 mg L −1 ) at 2 mL min −1 ; the system utilized a mutant (PP358) of the methane oxidizing bacterium Methylosinus trichosporium 0B3b for the fortuitous cooxidation of TCE by the enzyme-soluble methane monooxygenase (sMMO). A methane-free environment was maintained in the TCE treatment portion of the reactor (plug-flow columns), minimizing the effects of competitive inhibition between TCE and methane for the sMMO. The reactor was operated in two separate flow configurations, single-pass and cross-flow, with TCE removal percentages exceeding 78% (for a TCE feed concentration of 20 mg L −1 ) and 93% (for a TCE feed concentration of 10 mg L − 1), respectively. A r max of 109.4 mg of TCE (g of VS) −1 d −1 for a TCE feed concentration of 20 mg L −1 was obtained, suggesting that high rates of degradation occurred within the reactor. TCE-induced toxicity effects occurred at TCE feed concentrations of 10 mg L −1 and greater, resulting in declines of the biomass concentrations and the enzyme activities. However, the extent of this decline was alleviated by the addition of 0.2 M sodium formate. A model describing the rate of TCE degradation in the plug-flow columns was proposed by Alvarez-Cohen et al. and was modified to incorporate the suboptimal activities of sMMO. The model was adjusted to the data, and an apparent rate constant, k’, of 0.041 (dimensionless) was obtained. The effect of the finite transformation capacity term, T Cl in the model was noticeable only at high TCE feed concentrations. The model suggested that cross-flow operation was kinetically favored over single-pass operation due to enhanced TCE to biomass ratios. The model may be used to predict the extent of TCE degradation for a system and may serve as a useful tool for the optimization of flow rates. The optimization may include maximizing the rate of TCE degradation or minimizing the necessary residence time in a methane-starved environment. © 1995, American Chemical Society. All rights reserved.
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