Biomedical subjects

Daniel J Schell

Publications and source records attributed to Daniel J Schell.

6 recordsLinked to original sources

PubMed2007

Methodological analysis for determination of enzymatic digestibility of cellulosic materials.

Accurate measurement of enzymatic cellulose digestibility (X) is important in evaluating the efficiency of lignocellulose pretreatment technologies, assessing the performance of reconstituted cellulase mixtures, and conducting economic analysis for biorefinery processes. We analyzed the effect of sugars contained in enzymes solutions, usually added as a preservative, and random measurement errors on the accuracy of X calculated by various methods. The analysis suggests that exogenous sugars at levels measured in several commercial enzyme preparations significantly bias the results and that this error should be minimized by accounting for these sugars in the calculation of X. Additionally, a method of calculating X equating the ratio of the soluble glucose equivalent in the liquid phase after hydrolysis to the sum of the soluble glucose equivalent in the liquid phase and the insoluble glucose equivalent in the residual solid after hydrolysis was found to be the most accurate, particularly at high conversion levels (>ca. 50%).

Algorithms↗

PubMed2006

Contaminant occurrence, identification and control in a pilot-scale corn fiber to ethanol conversion process.

While interest in bioethanol production from lignocellulosic feedstocks is increasing, there is still relatively little pilot-plant data and operating experience available for this emerging industry. A series of batch and continuous fermentation runs were performed in a pilot-plant, some lasting up to six weeks, in which corn fiber-derived sugars were fermented to ethanol using glucose-fermenting and recombinant glucose/xylose-fermenting yeasts. However, contamination by Lactobacillus bacteria was a common occurrence during these runs. These contaminating microorganisms were found to readily consume arabinose, a sugar not utilized by the yeast, producing acetic and lactic acids that had a detrimental effect on fermentation performance. The infections were ultimately controlled with the antibiotic virginiamycin, but routine use of antibiotics is cost prohibitive. The severity of the problem encountered during this work is probably due to use of a highly contaminated feedstock. Lignocellulosic conversion facilities will not employ aseptic designs. Instead, techniques similar to those employed in the corn-based fuel ethanol industry to control infections will be used. Effective control may also be possible by using fermentative microorganisms that consume all biomass-derived sugars.

Ethanol↗

PubMed2004

A bioethanol process development unit: initial operating experiences and results with a corn fiber feedstock.

Interest in bioethanol production from lignocellulosic feedstocks for use as an alternative fuel is increasing, but near-term commercialization will require a low cost feedstock. One such feedstock, corn fiber, was tested in the US Department of Energy (DOE)/National Renewable Energy Laboratory (NREL) bioethanol pilot plant for the purpose of testing integrated equipment operation and generating performance data. During initial runs in 1995, the plant was operated for two runs lasting 10 and 15 days each and utilized unit operations for feedstock handling, pretreatment by dilute sulfuric-acid hydrolysis, yeast inoculum production, and simultaneous saccharification and fermentation using a commercially available cellulase enzyme. Although significant operational problems were encountered, as would be expected with the startup of any new plant, operating experience was gained and preliminary data were generated on corn fiber pretreatment and subsequent fermentation of the pretreated material. Bacterial contamination was a significant problem during these fermentations.

Biotechnology↗

PubMed2003

Dilute-sulfuric acid pretreatment of corn stover in pilot-scale reactor: investigation of yields, kinetics, and enzymatic digestibilities of solids.

Corn stover is a domestic feedstock that has potential to produce significant quantities of fuel ethanol and other bioenergy and biobased products. However, comprehensive yield and carbon mass balance information and validated kinetic models for dilute-sulfuric acid (H2SO4) pretreatment of corn stover have not been available. This has hindered the estimation of process economics and also limited the ability to perform technoeconomic modeling to guide research. To better characterize pretreatment and assess its kinetics, we pretreated corn stover in a continuous 1 t/d reactor. Corn stover was pretreated at 20% (w/w) solids concentration over a range of conditions encompassing residence times of 3-12 min, temperatures of 165- 195 degrees C, and H2SO4 concentrations of 0.5-1.4% (w/w). Xylan conversion yield and carbon mass balance data were collected at each run condition. Performance results were used to estimate kinetic model parameters assuming biphasic hemicellulose hydrolysis and a hydrolysis mechanism incorporating formation of intermediate xylo-oligomers. In addition, some of the pretreated solids were tested in a simultaneous saccharification and fermentation (SSF) process to measure the reactivity of their cellulose component to enzymatic digestion by cellulase enzymes. Monomeric xylose yields of 69-71% and total xylose yields (monomers and oligomers) of 70-77% were achieved with performance level depending on pretreatment severity. Cellulose conversion yields in SSF of 80-87% were obtained for some of the most digestible pretreated solids.

Animal Feed↗

PubMed2002

Use of measurement uncertainty analysis to assess accuracy of carbon mass balance closure for a cellulase production process.

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.

Biotechnology↗

PubMedDate not supplied

Carbon mass balance evaluation of cellulase production on soluble and insoluble substrates.

A methodology is described and applied for performing carbon mass balances across cellulase enzyme production processes using both soluble sugar and insoluble cellulose substrates. The fungus Trichoderma reesei was grown on either glucose, lactose, or cellulose in aerobic batch mode, and the evolution of the main carbonaceous components (cell mass, cellulose, soluble protein, adsorbed protein, sugars, and carbon dioxide) was followed. A variety of analytical techniques were utilized to measure these components, including (i) gravimetric analysis, (ii) near-infrared spectroscopy, (iii) bicinchoninic acid based soluble protein measurement, (iv) gas mass spectrometry and flow rate, (v) CHNS/O elemental analyses, and (vi) high-performance liquid chromatography. The combined set of measurements allowed carbon mass balances across the cellulase production process to be assessed to determine the consistency of the underlying kinetic data. Results demonstrate the capability to determine the levels and distribution of all major carbonaceous components during the cellulase production process on both soluble and insoluble substrates. Average carbon mass balance closures were near 100% during early stages (<72 h) of the cultivations using glucose, lactose, or cellulose as the substrates, but carbon mass closures trended high later in the cultivation. Analysis of carbon allocation results suggests that an error in the gas mass flow rate measurement was the primary cause for carbon mass balance closures to exceed 110% late in the process.

Bioreactors↗