METHANOTROPHIC TCE BIODEGRADATION IN A MULTISTAGE BIOREACTOR

A two-stage biorector system was continuously fed a solution of TCE (c oncentrations ranging between 0.2 and 20 mg L(-1)) at 2 mL min(-1); th e system utilized a mutant (PP358) of the methane oxidizing bacterium Methylosinus trichosporium OB3b for the fortuitous cooxidation of TCE by the enzyme-soluble methane monooxygenase (sMMO). A methane-free env ironment was maintained in the TCE treatment portion of the reactor (p lug-flow columns), minimizing the effects of competitive inhibition be tween TCE and methane for the sMMO. The reactor was operated in two se parate flow configurations, single-pass and crossflow, with TCE remova l 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)), respectivel y. A r(max) of 109.4 mg of TCE (g of VS)(-1) d(-1) for a TCE feed conc entration of 20 mg L(-1) was obtained, suggesting that high rates of d egradation occurred within the reactor. CE-induced toxicity effects oc curred at TCE feed concentrations of 10 mg L(-1) and greater, resultin g 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 w as adjusted to the data, and an apparent rate constant, K, of 0.041 (d imensionless) was obtained. The effect of the finite transformation ca pacity term, T-c, in the model was noticeable only at high TCE feed co ncentrations. The model suggested that cross-flow operation was kineti cally favored over single-pass operation due to enhanced TCE to biomas s ratios. The model may be used to predict the extent of TCE degradati on 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 d egradation or minimizing the necessary residence time in a methane-sta rved environment.