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CAB Reviews

A reviews journal covering agriculture, global health, nutrition, natural resources and veterinary science

CAB Review

Agricultural residues and energy crops as potentially economical and novel substrates for microbial production of butanol (a biofuel).

Abstract

This review describes the production of acetone butanol ethanol (ABE) from a variety of agricultural residues and energy crops employing biochemical or fermentation processes. A number of organisms are available for this bioconversion including Clostridium beijerinckii P260, C. beijerinckii BA101, Clostridium acetobutylicum and Clostridium saccharobutylicum P262. Some of these strains (P260 and P262) were used in an industrial setting in South Africa. One of the major limitations of these cultures is that none of them produce greater than 30 g/l total ABE unless integrated with simultaneous product recovery to reduce the toxicity of accumulated products. These cultures can utilize both hexose and pentose sugars derived from lignocellulosic hydrolysates such as maize (corn) fibre, wheat straw (one of the novel substrates), barley straw, maize stover and switchgrass. Substrates such as Jerusalem artichoke, maize, rye, millet, molasses, potato, soya molasses and agricultural wastes can also be used by the cultures listed. Additional carbohydrates that can be used include dextrins, fructose, sucrose and lactose. It is recommended that cultures that can produce greater amounts of ABE per litre of culture broth be developed. In order to economize the process of butanol production by fermentation, process technologies have been developed that integrate lignocellulosic biomass hydrolysis, fermentation and simultaneous product recovery. It should be noted that in continuous process where a product was recovered simultaneously, 461.3 g/l ABE was produced from 1125 g sugar in a 1 litre culture volume.