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Biobutanol has conventionally been generated by fermentation of carbohydrates derived from biomass (starch or sugar-based feedstock, such as corn) using Clostridia strains (mainly C. beijerinckii and C. acetobutylicum) under anaerobic conditions in batch mode. Under these premises, it has been tough for the acetone-butanol-ethanol fermentation to compete with petro-butanol production from an energy efficiency and material consumption standpoint. Challenges for butanol production from biomass comprised high cost of feedstock, scarcity of hyper-butanol producing bacteria and low butanol yield, volumetric productivity and titre, leading to high water usage and separation-purification costs. This article is an up-to-date review on several under explored sections, such as optimization of fermenter feed, microbial culture responsible for solvent production (co-culture techniques and electro-biochemical process), latest recovery techniques and the studies integrating in situ continuous fermentation processes. Biobutanol refinery way forward should build upon the use of low-cost lignocellulosic matter and zero cost organic wastes and by-products from food, agriculture, forestry, fermentation and paper industries as feedstock; optimized fermentation of such diversified feed with appropriate hyper-butanol producing strains in biofilm reactors and integration of fermentation step with hybrid high butanol-selective recovery techniques.

SUMMARY Biological hydrogen production from organic wastes is a less expensive, less energy-demanding, and environmentalfriendly process. Pure monoculture delivers low H2 content and low yield; these limitations are overcome by a defined co-culture system, which outperforms mixed cultures with increased H2 yield. The strategies used in co-culture systems for increasing H2 production have been discussed in this review. The strategies include hydrolysis of a variety of complex substrates, such as cellulose, molasses, crude glycerol, and algal biomass into simple fermentable sugars for increased H2 yield by eliminating the use of exogenous enzymes. The strategies can bring geographically distant isolated microorganisms from different sources to coexist for simultaneous utilization of substrate and end metabolites into H2 production of 99.99% purity without the expenses of reducing agents. In the case of maximum hydrogen production using co-culture strategies, Clostridium, Enterobacter, and photo-fermenting bacteria in a consolidated bioprocess system will result in increased H2 yield. A co-culture system is more feasible to achieve theoretical H2 yield with high conversion efficiency of organic wastes, enhance the economic viability of H2 production, provide better effluent treatment quality, and concurrently address the limitations of H2 production. Copyright © 2015 John Wiley & Sons, Ltd.