Acetone-butanol-ethanol fermentation

In acetone-butanol fermentation, acetone and butanol are produced from glucose using Clostridium, a strictly anaerobic bacterium. Further, ethanol is also produced and therefore this is also often called ABE fermentation. Two distinct metabolic pathways exist, one producing butanol from starch, the other producing butanol from sucrose. It yields 3 parts of acetone, 6 of butanol and 1 of ethanol.

ABE fermentation is one of the oldest known industrial fermentation with a history of more than 100 years. It ranked second only to ethanol fermentation in the first part of the 20th century, but disappeared in the second part due to the rise of the petrochemical industry. In 1861 butanol production through microbial fermentation was reported for the first time by Pasteur. This was followed by Schardinger in 1905 reporting production of acetone by fermentation. From 1912 to 1914 strains of Clostridium acetobutylicum were isolated by Chaim Weizmann which had the ability of fermenting starchy substrate. ABE fermentation was utilized to produce acetone during WWI to make the explosive cordite and in the production of synthetic rubber. In WWII, butanol was produced as fuel for fighter planes.

Interest in butanol as a biofuel has now revived, as it can be used as a direct gasoline substitute in unmodified internal combustion engines. Butanol when consumed in an internal combustion engine yields no SOX, NOX or carbon monoxide all environmentally harmful byproducts of combustion. CO2 is the combustion byproduct of butanol, and is considered environmentally 'green'.Butanol is far less corrosive than ethanol and can be shipped and distributed through existing pipelines and filling stations. Butanol solves the safety problems associated with the infrastructure of the hydrogen supply. Reformed butanol has four more hydrogen atoms than ethanol, resulting in a higher energy output and is used as a fuel cell fuel. Butanol is an industrial commodity, with a 370 million gallons per year market with a selling price of $3.75 per gallon.

Feedstocks

• molasses and starch (e.g. out of maize, wheat, rye,...) - all fairly expensive
• The Jerusalem artichoke is an agricultural crop with considerable potential as a carbohydrate substrate for ABE fermentation. Short oligomeric fructans are the main carbohydrate forms which occur in the tuber. They must be hydrolyzed by acid or inulase prior to fermentation.
• Cheese whey is a good alternative ABE fermentation substrate because of its lactose content and availability. Cheese whey contains relatively low sugar (4-5 % lactose) and so it is not suitable for most fermentations without prior concentration. But it is suitable for ABE fermentation because the sugar consume of clostridia is limited by product toxicity.
• Apple pomace is a solid agricultural waste and it contains about 10 % (wt/wt) carbohydrates (67 % fructose, 23 % glucose and 10 % sucrose).
• Algal biomass is also considered to become a suitable fermentation substrate because of advantages in utilization and bioconversion.
• Straw is a representative of lignocellulosic plants and is one of the most abundant renewable resources all over the world. Components such as cellulose and hemicellulose can be degraded and utilised . Prior degradation can be done via "steam-explosion", acid hydrolyses (e.g. pre-treatment with sulphuric acid) and enzymatic hydrolyses (pre-treatment or cofermentation with cellulases).

See Also

• Acetone-butanol-ethanol fermentation
• Clostridium acetobutylicum