The most common procedures for characterizing the chemical components
of lignocellulosic feedstocks use a two-stage sulfuric acid hydrolysis
to fractionate biomass for gravimetric and instrumental analyses.
The uncertainty (i.e., dispersion of values from repeated measurement)
in the primary data is of general interest to those with technical
or financial interests in biomass conversion technology. The composition
of a homogenized corn stover feedstock (154 replicate samples in 13
batches, by 7 analysts in 2 laboratories) was measured along with
a National Institute of Standards and Technology (NIST) reference
sugar cane bagasse, as a control, using this laboratory's suite of
laboratory analytical procedures (LAPs). The uncertainty was evaluated
by the statistical analysis of these data and is reported as the standard
deviation of each component measurement. Censored and uncensored versions
of these data sets are reported, as evidence was found for intermittent
instrumental and equipment problems. The censored data are believed
to represent the “best case” results of these analyses,
whereas the uncensored data show how small method changes can strongly
affect the uncertainties of these empirical methods. Relative standard
deviations (RSD) of 1−3% are reported for glucan, xylan, lignin,
extractives, and total component closure with the other minor components
showing 4−10% RSD. The standard deviations seen with the corn
stover and NIST bagasse materials were similar, which suggests that
the uncertainties reported here are due more to the analytical method
used than to the specific feedstock type being analyzed.
Projected life cycle greenhouse gas (GHG) emissions and net energy value (NEV) of high-ethanol blend fuel (E85) used to propel a passenger car in the United States are evaluated using attributional life cycle assessment. Input data represent national-average conditions projected to 2022 for ethanol produced from corn grain, corn stover, wheat straw, switchgrass, and forest residues. Three conversion technologies are assessed: advanced dry mill (corn grain), biochemical (switchgrass, corn stover, wheat straw), and thermochemical (forest residues). A reference case is compared against results from Monte Carlo uncertainty analysis. For this case, one kilometer traveled on E85 from the feedstock-to-ethanol pathways evaluated has 43%-57% lower GHG emissions than a car operated on conventional U.S. gasoline (base year 2005). Differences in NEV cluster by conversion technology rather than by feedstock. The reference case estimates of GHG and NEV skew to the tails of the estimated frequency distributions. Though not as optimistic as the reference case, the projected median GHG and NEV for all feedstock-to-E85 pathways evaluated offer significant improvement over conventional U.S. gasoline. Sensitivity analysis suggests that inputs to the feedstock production phase are the most influential parameters for GHG and NEV. Results from this study can be used to help focus research and development efforts.
In the context of algal biofuels, lipids, or better aliphatic chains of the fatty acids, are perhaps the most important constituents of algal biomass. Accurate quantification of lipids and their respective fuel yield is crucial for comparison of algal strains and growth conditions and for process monitoring. As an alternative to traditional solvent-based lipid extraction procedures, we have developed a robust whole-biomass in situ transesterification procedure for quantification of algal lipids (as fatty acid methyl esters, FAMEs) that (a) can be carried out on a small scale (using 4–7 mg of biomass), (b) is applicable to a range of different species, (c) consists of a single-step reaction, (d) is robust over a range of different temperature and time combinations, and (e) tolerant to at least 50% water in the biomass. Unlike gravimetric lipid quantification, which can over- or underestimate the lipid content, whole biomass transesterification reflects the true potential fuel yield of algal biomass. We report here on the comparison of the yield of FAMEs by using different catalysts and catalyst combinations, with the acid catalyst HCl providing a consistently high level of conversion of fatty acids with a precision of 1.9% relative standard deviation. We investigate the influence of reaction time, temperature, and biomass water content on the measured FAME content and profile for 4 different samples of algae (replete and deplete Chlorella vulgaris, replete Phaeodactylum tricornutum, and replete Nannochloropsis sp.). We conclude by demonstrating a full mass balance closure of all fatty acids around a traditional lipid extraction process.FigureAccurate quantification of different types of lipids in algal biomass using a comprehensive study of reaction parameters.Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-012-5814-0) contains supplementary material, which is available to authorized users.
Whole cells deposited on a titanium dioxide-coated
surface have been oxidized in air to carbon dioxide via
photocatalysis. This paper provides the first evidence that
the organic matter in whole cells can be completely
oxidized. Three experimental techniques were employed
to monitor this reaction: scanning electron microscopy,14C
radioisotope labeling, and batch reactor measurements.
The scanning electron microscopy experiments illustrate the
disappearance of Escherichia coli cell mass. The 14C
radioisotope labeling experiments establish that the carbon
content of E. coli is oxidized to form carbon dioxide with
substantial closure of the mass balance. The batch reactor
experiments corroborate the mass balance and provide
a preliminary indication of the rate of the oxidation reaction.
These results provide evidence that a photocatalytic
surface used for disinfection can also be self-cleaning in
an air−solid system.
Maize (Zea mays L.) stover has been identified as an important feedstock for the production of cellulosic ethanol. Our objectives were to measure hybrid effect and combining ability patterns of traits related to cellulosic ethanol production, determine if germplasm and mutations used for silage production would also be beneficial for feedstock production, and examine relationships between traits that are relevant to selective breeding. We evaluated grain hybrids, germplasm bred for silage production, brown‐midrib hybrids, and a leafy hybrid. Yield and composition traits were measured in four environments. There was a 53% difference in stover yield between commercial grain hybrids that were equivalent for other production‐related traits. Silage germplasm may be useful for increasing stover yield and reducing lignin concentration. We found much more variation among hybrids than either in vitro ruminal fermentability or polysaccharide concentration. Correlations between traits were mostly favorable or nonexistent. Our results suggest that utilizing standing genetic variation of maize in breeding programs could substantially increase the amount of biofuels produced from stover per unit area of land.
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