title: Use of measurement uncertainty analysis to assess accuracy of carbon mass balance closure for a cellulase production process.
abstract: Closing carbon mass balances is a critical and necessary step for verifying the performance of any conversion process. We developed a methodology for calculating carbon mass balance closures for a cellulase production process and then applied measurement uncertainty analysis to calculate 95% confidence limits to assess the accuracy of the results. Cellulase production experiments were conducted in 7-L fermentors using Trichoderma reesei grown on pure cellulose (Solka-floc), glucose, or lactose. All input and output carbon-containing streams were measured and carbon dioxide in the exhaust gas was quantified using a mass spectrometer. On Solka-floc, carbon mass balances ranged from 90 to 100% closure for the first 48 h but increased to 101 to 135% closure from 72 h to the end of the cultivation at 168 h. Carbon mass balance closures for soluble sugar substrates ranged from 92 to 127% over the entire course of the cultivations. The 95% confidence intervals (CIs) for carbon mass balance closure were typically +/-11 to 12 percentage points after 48 h of cultivation. Many of the carbon mass balance results did not bracket 100% closure within the 95% CIs. These results suggest that measurement problems with the experimental or analytical methods may exist. This work shows that uncertainty analysis can be a useful diagnostic tool for identifying measurement problems in complex biochemical systems.
authors.affiliation: National Renewable Energy Laboratory, Golden, CO 80401, USA. dan_schell@nrel.gov
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Schell
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Sáez
authors.forename: Jenny
authors.initials: J
authors.lastname: Hamilton
authors.forename: Arun
authors.initials: A
authors.lastname: Tholudur
authors.forename: James D
authors.initials: JD
authors.lastname: McMillan
mesh_terms: D001709:Biotechnology / Q000379:methods; D002244:Carbon / Q000032:analysis*; D002480:Cellulase / Q000378:metabolism*; D007700:Kinetics; D015203:Reproducibility of Results; D013379:Substrate Specificity; D003313:Zea mays / Q000201:enzymology
chemical_list: D002244:Carbon; D002480:Cellulase