The transfer to industrial scale production of ethanol from various sources of cellulosic biomass, is of three main elements: identifying and obtaining or vegetable raw materials with the highest concentration of carbohydrates, the establishment point grinding processes saccharification and economically viable to release simple sugars contained in these carbohydrates and identification of microorganisms with the gene to ferment all of these sugars. Results from recent studies conducted by researchers at the ARS / USDA have been the subject of articles in scientific journals such as Biotechnology and Bioengineering, the Journal of Biobased Materials and Bioenergy and the Journal of Industrial Microbiology and Biotechnology. This research focuses on two types of projects: first the development of a protocol for the transformation of wheat straw into ethanol and secondly, the characterization of bacteria infecting plants producing ethanol and interfering with fuel production.
A study of five years was conducted by researchers at the ARS National Center for Agricultural Utilization Research (NCAUR) in Peoria, Illinois: it was designed to determine whether wheat straw, crop residue grains of wheat, had a commercial potential for the production of cellulosic ethanol. It has been demonstrated that pretreatment of this type of plant residues with alkaline peroxide, followed by enzymatic hydrolysis, freeing and ferment almost all the sugar plant. This process, called enzymatic saccharification, “would even release the sugars from the cell wall, inaccessible. It would also increase significantly the efficiency of ethanol production to about 93 gallons per ton of wheat straw and would present the advantage of not producing fermentation inhibitors.
ARS scientists have also demonstrated that pretreatment of wheat straw with lime, would achieve a good performance, about 83 gallons of ethanol per ton of wheat. The use of lime to prevent even the co inhibitors of fermentation and produce easily fermentable sugars. This approach would have the added advantage of being much less expensive than pretreatment with alkaline peroxide.
Regarding fermentation, a bacterial strain of E. coli has been preferred over yeast normally used. Indeed, yeasts are not able to ferment all the sugars released from cellulosic biomass: including sugars, contained in cell walls, such as cellulose and hemicellulose. Therefore, a strain of E. coli genetically modified to increase capacity of fermentation was tested. It is able to maintain sustainable rates of fermentation are necessary for production on an industrial scale. These results were obtained for 10-liter fermentors, it remains to pass tests in 100 liters and an analysis of production costs of this industrial process.
But these same environments conducive to fermentation can also promote the development of microorganisms that infect the infrastructure for ethanol production and decrease yields. They are usually bacteria growing rapidly in environments with low pH and high concentration of alcohol, conditions met during the production of ethanol. Samples on site revealed that most of these bacteria were lactic acid bacteria. A simulation model of small-scale stirring of contamination and bacterial infection has been developed. This has highlighted a culture inoculation tests with Lactobacillus fermentum, one of the most common sources of bacterial infection in plants producing ethanol, the yield of ethanol decreased by 27%. The bacteria metabolize sugar for its own growth and produces lactic acid and acetic acid, which inhibits the yeast fermentation. The infection can sometimes be treated with antibiotics, but a resistant strain has been identified.
ARS scientists have designed this model becomes a tool for industry to produce ethanol and help develop alternative methods to control bacterial contamination of the peaks and improve production processes. These research priorities are part of the LRA which, among other things, develop new sources of bioenergy and are part of two research programs “Bioenergy and Energy Alternatives” and “Quality and Utilization of Agricultural Products”.
USDA and DOE have announced their plans in May 2010 to finance up to 33 million dollars of R & D focused on technologies and processes for the production of biofuels, bioenergy and Renewable Products (s ) (Original) Plants (GRP). These funds are part of the “Biomass Research and Development Initiative (BRDI)” which focuses on technical areas such as development of raw materials, biofuels and renewable products plant and the economic analysis of biofuel development .
- Cellulosic Ethanol: Expanding Options Identifying Barriers – ARS / USDA News & Events – 09/04/2010 – http://www.ars.usda.gov/is/pr/2010/100409.htm
- Niches and Glitches in Ethanol Production – ARS / USDA News & Events – 05/04/2010 – http://www.ars.usda.gov/is/AR/archive/apr10/ethanol0410.htm
- Federal Technology Watch, 10/05/2010
|Category: Food Science||Tags: BioEnergy, biofuels, enzymatic hydrolysis, wheat straw|