| Biohydrogen production from cellulosic waste materials using dark fermentation is a promising technology for producing renewable energy. The purpose of this study was to evaluate residual cellulosic materials generated from local sources for their H2 production potential and to characterize growth of Clostridium thermocellum, during fermentation of a cellulosic substrate under continuous culture conditions. C. thermocellum ATCC 27405, is a cellulolytic, thermophilic bacterium that has been shown to be capable of H2 production on both cellobiose and cellulosic substrates. The complex cellulosic materials tested were dried distillers grain (DDGs), barley hulls (BH) and Fusarium head blight contaminated barley hulls (CBH). Several simultaneous batch fermentation experiments were conducted in order to quantify H2 production, and to determine soluble end-product synthesis patterns. Overall, the dried distillers grain produced the highest concentration of hydrogen gas at 1.27 mmol H2/glucose equivalent utilized. CBH and BH produced 1.18 and 1.24 mmol H2/glucose equivalent utilized, respectively. Overall, this study indicates that hydrogen derived from a variety of cellulosic waste biomass sources is a possible candidate for the development of sustainable energy. Continuous hydrogen (H2) production during fermentation of alpha-cellulose was established using a 5 L fermentor. Growth experiments were maintained for over 3000 hours. Substrate concentrations varied between 1 to 4 g L-1. Continuous sparging with nitrogen gas was used to prevent clogging of the feed-line. The pH and temperature of the reactor were maintained throughout the experiment. At concentrations above 4 g L-1, the delivery of alpha-cellulose was impaired due to feed-line clogging and it became difficult to maintain a homogenous suspension. The highest total gas (H2 plus CO 2) production rate, 56.6 ml L-1 hr-1 , was observed at a dilution rate of 0.042 h-1 and substrate concentration of 4 g L-1. Under these conditions, the H2 production rate was 5.06 mmol hr-1. Acetate and ethanol were the major soluble end-products, while lactate and formate were greatly reduced compared to production in batch cultures. Concentrations of all metabolites increased with increasing substrate concentration, with the exception of lactate. This data has increased knowledge of H2 gas production via direct fermentation of an insoluble cellulosic substrate under continuous culture conditions. These results show that H2 production is proportional to substrate concentration, but product ratios remain constant within the loading rates tested. |
