Experimental evaluation and mathematical modeling of the fundamental processes affecting TCE co-oxidation by the sMMO enzyme system of Methylosinus trichosporium OB3B

A two-stage, pressurized bioreactor has been developed for the continuous enzymatic co-oxidation of trichloroethylene (TCE) by the methanotroph Methylosinus trichosporium 0B3b. This bacteria utilizes the non-specific enzyme, soluble methane monooxygenase (sMMO), for growth on methane and TCE co-oxidation. Correlations between the sMMO activity and oxidation rates have been established. TCE removal percentages ranged between 100% and 79% for TCE feed concentrations ranging between 0.2 and 20 mg L^-1 respectively. Both TCE-epoxide induced sMMO specific toxicity and whole-cell TCE toxicity were apparent at high TCE feed concentrations. Sodium formate addition enhanced the recovery of the sMMO, due to increased specific NADH concentrations necessary for enzyme production. The conditions in the bioreactor were such that mass transfer resistance was negligible, and the bioreactor provided suitable data for the development of a mechanistically and biochemically based model describing TCE oxidation as two substrates (methane and TCE) competing for the active site of one enzyme with cofactor (NADH) activation of the enzyme. The structured model predicts both the state of the bacteria and the state of the bacteria's environment based on initial conditions. The rate constant for TCE degradation was estimated to be 0.047 (dimensionless). The model was used to simulate the bioreactor for TCE feed concentrations of 1 and 10 mg L^-1, and the model predicted the TCE concentrations, biomass concentrations, and specific sMMO activities within 25% after a simulation length of 17 days. The simulation was also run utilizing the empirical model proposed by Chang et al. (1995), which showed large deviations for both TCE removal (14% deviation) and biomass concentration prediction (75% deviation). The sMMO activity is correlated with the rate of TCE oxidation. Biomass concentrations, alone, may not describe the potential of the bacteria to degrade TCE. The experimental study and the simulations refute the use of the finite transformation capacity as adequately representing TCE induced toxicity effects. The model developed during this study is structured, mechanistic, and based on fundamental enzyme kinetics and the biochemistry of the organism, and the model may be useful as a predictive estimator for feasibility testing, process development, and process design.