Scientists develop biobutanol from wheat straw

Scientists from the U.S. Department of Agriculture's Agricultural Research Service (ARS) are experimenting with a way to convert cellulosic biomass into biobutanol using the bacterium Clostridium beijerinckii.

Biobutanol (butyl alcohol) can become an important renewable transportation fuel because it has a higher energy content than ethanol. It can be used in the existing gasoline supply and distribution lines, has higher octane number, and can be mixed with gasoline in any proportion (earlier post). It is also a valuable chemical.

Biobutanol can be readily be produced from any starch source, obtained from annual crops such as corn, rice or barley. However, due to the prohibitive cost of these grains and cereals and because of the need to balance food and fuel production, use of lignocellulosic biomass residues is the way forward.

The ARS scientists report in Biotechnology for Fuels and Chemicals that a microbial culture such as Clostridium beijerinckii P260 can utilize five and six carbon sugars present in cellulosic biomass and convert them to butanol.

In order to reduce the cost of butanol production, the researchers hydrolyzed wheat straw to lignocellulosic component sugars (glucose, xylose, arabinose, galactose, and mannose) prior to their conversion to butanol. The rate of production of wheat straw hydrolysate to butanol was 214% over that from glucose:
bioenergy :: biofuels :: energy :: sustainability :: cellulose :: straw :: biomass :: sugars :: biobutanol ::

Wheat straw was pretreated with dilute sulfuric acid and hydrolyzed to simple sugars using commercial carbohydrases. Hydrolysis, fermentation, and product recovery were combined in a single step using a 2.5 L bioreactor. Pretreated wheat straw was successfully hydrolyzed to produce glucose, xylose, arabinose, galactose, and mannose, and these sugars were fermented by C. beijerinckii.

The fermentation performance was enhanced by simultaneously recovering products [Acetone-butanol (AB)] from the fermentation broth by gas stripping, thereby, avoiding end product inhibition. The reactor was operated in a fed-batch mode, and the fermentation lasted for more than 500 hours.

These studies, part of a larger project called Cost-Effective Bioprocess Technologies for Production of Biofuels from Lignocellulosic Biomass, demonstrated that production of AB from wheat straw in a single reactor is possible when hydrolytic enzymes are used and product (AB) is simultaneously produced and recovered.

Successful production of economically available butanol from wheat straw by fermentation will benefit farmers, the butanol producing industry and the public at large. Development of such a fuel by an economically viable process is essential as gasoline prices are rising steadily.

Biobutanol made headlines when DuPont and BP announced they were going to collaborate on producing the fuel, which they think holds promise over the longer term as a gasoline substitute (earlier post). Another player is biotech company Green Biologics who received a large (€855,000) fund to research strategies to develop the fuel from cellulosic biomass (see here).

References:
Qureshi, N., Saha, B.C., Cotta, M.A., "Bioconversion of wheat straw to butanol (a superior liquid fuel): simultaneous saccharification, fermentation, and product recovery", [*abstract], Biotechnology for Fuels and Chemicals, Paper No. 4-16, May 2, 2007.