(123d) Acetone-Butanol-Ethanol (ABE) Production from Fermentation of Hot-Water Extracted Hemicellulose Hydrolysate of Woody Biomass
In Kraft pulping process, a large fraction of hemicellulose of wood is discharged into black liquor recovering only its heating value, thus underutilizing the carbohydrate resource. In this study, the hemicellulose portion of pulp feed was investigated as feedstock for acetone-butanol-ethanol (ABE) fermentation using Clostridium acetobutylicum. For this purpose, hot-water treatment was applied to Poplar (hardwood) and Southern pine (softwood) to extract the hemicellulose portion prior to the pulping process without degrading the quality of the cellulose fiber. In ABE fermentation by Clostridium acetobutylicum, both glucose and xylose are utilized as carbon source giving similar yields in solvent production. In this work, the culture was shown to consume up to 57 g/L of hexose or xylose, producing ABE solvents at the levels of 17-18 g/L with a total solvent yield of 30-31% (g-solvent/g-sugar). During the hemicellulose extraction process, various toxins are generated including furfural, HMF and lignin-degraded phenolic compounds. The hemicellulose hydrolysate was therefore detoxified prior to fermentation. The effectiveness of different detoxification methods; overliming, ion-exchange and activated carbon adsorption, is assessed. Another issue in the process was that hot-water treatment produces hemicellulose sugars in oligomers. It needs to be hydrolyzed to monomers before it can be metabolized by the microorganism. Thus a SSF scheme was employed incorporating Clostridium acetobutylicum and commercial enzymes having xylanase and mannanase activities. The process details of hot-water extraction, performance of detoxification as well as the bioconversion profiles are presented.