Lh. Smith et al., NUMERICAL MODELING AND UNCERTAINTIES IN RATE COEFFICIENTS FOR METHANEUTILIZATION AND TCE COMETABOLISM BY A METHANE-OXIDIZING MIXED CULTURE, Biotechnology and bioengineering, 53(3), 1997, pp. 320-331
The rates of methane utilization and trichioroethylene (TCE) cometabol
ism by a methanotrophic mixed culture were characterized in batch and
pseudo-steady-state studies. Procedures for determination of the rate
coefficients and their uncertainties by fitting a numerical model to e
xperimental data are described. The model consisted of a system of dif
ferential equations for the rates of Monod kinetics, cell growth on me
thane and inactivation due to TCE transformation product toxicity, gas
/liquid mass transfer of methane and TCE, and the rate of passive loss
es of TCE. The maximum specific rate of methane utilization (K-CH4) wa
s determined by fitting the numerical model to batch experimental data
, with the initial concentration of active methane-oxidizing cells (X(
O)(a)) also used as a model fitting parameter. The best estimate of k(
CH4) was 2.2 g CH4/g cells-d with excess copper available, with a sing
le-parameter 95% confidence interval of 2.0-2.4 mg/mg-d. The joint 95%
confidence region for k(CH4) and X(d)(O) is presented graphically. Th
e half-velocity coefficient (K-S,K-CH4) was 0.07 mg CH4/L with excess
copper available and 0.47 mg CH4/L under copper limitation, with 95% c
onfidence intervals of 0.02-0.11 and 0.35-0.59 mg/L, respectively. Uni
que values of the TCE rate coefficients k(TCE) and K-S,K-TCE could not
be determined because they were found to be highly correlated in the
model fitting analysis. However, the ratio k(TCE)/K-S,K-TCE and the TC
E transformation capacity (T-C) were well defined, with values of 0.35
L/mg-day and 0.21 g TCE/g active cells, respectively, for cells trans
forming TCE in the absence of methane or supplemental formate. The sin
gle-parameter 95% confidence intervals for k(TCE)/K-S,K-TCE and T-C we
re 0.27-0.43 L/mg-d and 0.18-0.24 g TCE/g active cells, respectively.
The joint 95% confidence regions for k(TCE)/(S,TCE), and T-C are prese
nted graphically. (C) 1997 John Wiley & Sons, Inc.