Tuesday, May 1, 2012: 10:00 AM
Rhythms Ballroom, 2nd fl (Sheraton New Orleans)
Switchgrass (SWG) is considered one of the most promising energy crops for the U.S. conditions and its production is predicted to significantly increase up to 10-times within the next 10 years. With a carbohydrate content in excess of 65% and lignin content of less than 20%, SWG presents an attractive and relatively inexpensive feedstock (average price of $40-50/dry t) for hydrogen (H2) production. However, the efficient conversion of the carbohydrate component of SWG to fermentable sugars requires biomass pretreatment, which contributes on average 20% to the total production costs, and currently limits the commercial feasibility of biohydrogen. It would therefore be cost-beneficial if lignocellulosic biomass is directly converted to H2 without a prior chemical or enzymatic pretreatment. With this as an objective, a thermophilic bacterium, Caldicellulosiruptor saccharolyticus DSM 8903, was adapted in a mineral salt medium containing SWG at 65°C for a period of three months with continuous sub-culturing. Thereafter, in batch fermentation experiments conducted under dark anaerobic conditions, C. saccharolyticus produced a maximum of 14.3 mmol H2/L (396 ml H2/L) after 6 days h with estimated SWG consumption of 1.6 g/L and yield of 248 ml H2/g SWG. In comparison, the strain produced 23.3 mmol H2/L on cellulose, which represents a 1.6-fold increase over that achieved on SWG for the same incubation period of 6 days. No accumulation of glucose, xylose, arabinose, galactose and mannose in the fermentation broth was observed. The H2 production capabilities of C. saccharolyticus on complex substrates and simple sugars will be evaluated and discussed.