The increase in prices of petroleum based fuels, future depletion of worldwide petroleum reserves and environmental
policies to reduce CO2 emissions have stimulated research into the development of biotechnology to produce chemicals
and fuels from renewable resources. The most commonly used metabolically derived biofuels are hydrogen, acetone,
butanol and ethanol. Biofuel is produced biologically from renewable biomass by Clostridium spp. under strictly anaerobic
condition. Substrate costs can make up to about 63% of the total cost of biofuel production. This is not because of the
expense of the substrate itself, but mainly because of the low efficiency of Clostridium to convert substrate into biofuel,
i.e. the yield of biofuel is often low, and this together with the formation of by-products leads to a high cost for butanol
recovery. In addition, the maintenance of strict anaerobic conditions for Clostridium requires special conditions e.g.
addition of costly reducing agents, and flushing with N2 gas, which increase the cost of the fermentation process. Hence,
substrates such as agricultural residues, including wheat straw, barley straw, maize stover, wood hydrolysate, and
switchgrass as well as dairy industry waste offer potential alternatives. To reduce the costs of producing hydrogen and
ABE from fermentation, include using a low cost fermentation substrate and/or optimizing the fermentation conditions to
improve the efficiency of converting substrate to biofuel. The facultative anaerobes are able to consume O2 in a medium
and so a steady anaerobic condition in a fermentor was attained without addition of any reducing agent. Significant
progress has been made towards genetically engineering clostridia to utilize a variety of substrates, and to reduce the need
for pretreatment processes as well as reduce the application of reducing agents for creation anaerobic conditions. Among
the cheap and readily available substrates for biohydrogen and liquid biofuel production, agro-industrial wastes are
possibly one of the better choices. The possibility of using cheaper resources, such as lignocelluloses, whey cheese or any
agro-industrial and domestic organic wastes, as the alternative substrates for biofuel production over more expensive
substrates . Selection of cellulolytic clostridia in applying biotechnology to acetone-butanol fermentation revived interest
in research on solvent production by fermentation.