Challenges for biohydrogen production via direct lignocellulose fermentation

Direct cellulose fermentation by cellulolytic anaerobic bacteria offers potential to generate renewable hydrogen (H-2) from inexpensive waste cellulosic feedstocks. The rates and yields of H-2 production via direct cellulose fermentation are low and must be increased significantly if this technology is to become a viable method for generating usable H-2. A much more comprehensive understanding of the relationships between gene and gene product expression, end-product synthesis patterns, and the factors that regulate carbon and electron balance, within the context of the bioreactor conditions must be achieved if we are to improve molar yields of H-2 during cellulose fermentation. Strategies to increase yields of H-2 production from cellulose include manipulation of carbon and electron flow via end-product inhibition (metabolic shift), metabolic engineering at the genetic level, synergistic co-cultures, and bioprocess engineering and bioreactor designs that maintain a neutral pH during fermentation and ensure rapid removal of H-2 and CO2 from the aqueous phase. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.