Numerical modeling and uncertainties in rate coefficients for methane utilization and TCE cometabolism by a methane-oxidizing mixed culture

✍ Scribed by Laurence H. Smith; Peter K. Kitanidis; Perry L. McCarty

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 162 KB
• Volume: 53
• Category: Article
• ISSN: 0006-3592
• DOI: 10.1002/(sici)1097-0290(19970205)53:3<320::aid-bit11>3.0.co;2-o

✦ Synopsis

The rates of methane utilization and trichloroethylene (TCE) cometabolism 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 experimental data are described. The model consisted of a system of differential equations for the rates of Monod kinetics, cell growth on methane and inactivation due to TCE transformation product toxicity, gas/liquid mass transfer of methane and TCE, and the rate of passive losses of TCE. The maximum specific rate of methane utilization (K CH 4 ) was determined by fitting the numerical model to batch experimental data, with the initial concentration of active methane-oxidizing cells (X a 0 ) also used as a model fitting parameter. The best estimate of k CH 4 was 2.2 g CH 4 /g cells-d with excess copper available, with a singleparameter 95% confidence interval of 2.0-2.4 mg/mg-d. The joint 95% confidence region for k CH 4 and X d 0 is presented graphically. The half-velocity coefficient (K S,CH 4 ) was 0.07 mg CH 4 /L with excess copper available and 0.47 mg CH 4 /L under copper limitation, with 95% confidence intervals of 0.02-0.11 and 0.35-0.59 mg/L, respectively. Unique values of the TCE rate coefficients k TCE and K S,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,TCE and the TCE 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 transforming TCE in the absence of methane or supplemental formate. The singleparameter 95% confidence intervals for k TCE /K S,TCE and T C were 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 / K S,TCE and T C are presented graphically.