Hydrolysis and Fermentation for Cellulosic Ethanol Production

Book chapter, 2015

This chapter summarizes the hydrolysis technologies and bioconversion processes employed for cellulosic ethanol production. Hydrolysis process involves pre-treatment methods (first-stage hydrolysis) and enzymatic hydrolysis (second-stage hydrolysis). Although cellulose is mainly present as crystalline fibers that are highly resistant to hydrolysis, its content in biomass is typically larger compared to hemicellulose and, as a result, cellulases are the key enzymes for bioethanol production. The major bioconversion processes are: The separate (or sequential) hydrolysis and fermentation (SHF), the simultaneous saccharification and fermentation (SSF) and the consolidated bioconversion process (CBP). Many yeast species have been reported to convert simple sugars to ethanol under anaerobic conditions. S. cerevisiae, Pichia stipitis, P. kudriavzevii (Candida krusei), Kluveromyces marxianus, C. shehatae, C. tropicalis, C. guilliermondii, and Pachysolen tannophilus are among the most often used yeast species in biomass-derived sugars-to-ethanol conversion processes.