Challenges for biohydrogen production via direct lignocellulose fermentation

Abstract 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 CO 2 from the aqueous phase.