Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
The addition of sodium metabisulfite (0.5 mM) to fermentation broth together with low amounts of air in the headspace was found to dramatically improve the growth and fermentation of acid-pretreated sugarcane bagasse (180°C, 10 min, 1% phosphoric acid) by Escherichia coli MM160. This biocatalyst was able to directly ferment the C-6 and C-5 sugars during simultaneous saccharification and co-fermentation (10% dry weight including fiber and solubles) at 37°C (pH 6.5) without liquid/solid separation or sugar cleanup. A 6-h liquefaction step (5 FPU/g bagasse dry weight, 55°C) was included to improve mixing, immediately prior to inoculation, forming an L+SScF process. Glucose and cellobiose were metabolized more rapidly than xylose without air and bisulfite. Some sugars remained in the fermentation broth even after 144 h. When bisulfite alone was added, the rate of sugar utilization increased. With small amounts of air supplied into the headspace, sugar utilization was nearly complete. Final yields after 144 h were 0.16 g ethanol/g bagasse dry weight (200 L/tonne; 48 gal/US ton) for the control and 0.20 g ethanol/g bagasse dry weight (250 L/tonne; 61 gal/US ton) for either bisulfite alone or air in the headspace. With the combination of both bisulfite and air, fermentation time was reduced to 96 h with the production of over 0.25 g ethanol/g bagasse dry weight (313 L/tonne; 76 gal/US ton). Chemicals used in phosphoric acid pretreatment process and fermentation (ammonia, magnesium sulfate, trace metals) are primary components of fertilizer. Cost for these could be shared between biomass production and processing.