Hydrogen Production via Fermentation of Avicel and Corn Stover In a Sequencing Batch Reactor

When produced from lignocellulosic waste materials, hydrogen is one of the most promising options for a net-zero emission energy carrier however, costs and scalability of the process remain barriers to large-scale production. Advances in consolidated bioprocessing must be made to improve the rates of cellulose hydrolysis and its subsequent fermentation to H₂. This study aims to use the attachment properties of the cellulosome of Clostridium thermocellum to maintain high concentrations of bacteria and enzyme in a sequencing batch reactor (SBR), thereby improving the rates of cellulose hydrolysis and H₂ production. SBR mode was initiated by running a 2.5 g/L fermentation for 24 hours followed by settling the unfermented solid substrate along with any attached bacteria for one hour. This was followed by removing 1L of the supernatant, and adding 1L of fresh media and substrate and restarting agitation. Four cycles were completed for each condition tested. By varying the carbon concentration, hydrolic residence time (HRT) and displacement volume, we were able to acheive the optimal conditions for maximum hydrogen production.  Results indicate that at a carbon loading of 2.5 g/L/day, the substrate was fully consumed and the bacteria did not settle when agitation was turned off. At 5.0 g/L/d, we observed an excess of substrate present in the reactor, and protein concentrations before and after settling indicated approximately 80% of the bacterial biomass was retained.  After 4 cycles at this condion, the average rate of hydrogen production increased from 0.60 to 0.92 mmol/L/hr, illustrating another benefit of adapting the bacteria to it's substrate.