The sugar available for fermentatio

The sugar available for fermentation after the pretreatment and hydrolysis of biomass can be either
heterogeneous like sucrose and glucose when originated from lignocellulosic biomass. Thus, the main
bulk of biomass used for ethanol production are two types of sugars, the disaccharide sucrose and the
monosugar glucose, both of them can easily be fermented to ethanol by the traditional baker’s yeast, S.
cerevisae.
3.3 Ethanol and hydrogen production by separate hydrolysis and fermentation (SHF)
The maximum yield of ethanol (9.69 g/L) was achieved after 72 h of S. cerevisiae cultivation with no
hydrogen production (Fig. 2a). S. cerevisiae, commercial ethanol-producing bacteria, has many
advantages over other known ethanol producing microorganisms. The most important are high ethanol
yields, ethanol tolerance, high robustness and high resistance to toxic inhibitors.
Lower production of ethanol (1.38 g/L) was observed after 72 h by E. aerogenes. However, E.
aerogenes yielded high hydrogen production (1,416 mL/L) after 12 h of cultivation (Fig. 2b). E.
aerogenes can convert various carbohydrates, such as sugars and sugar alcohols, to H2, ethanol, 2,3-
butanediol, lactate and acetate. Ito et al. [16] reported that E. aerogenes HU-101 mainly produces H2 and
ethanol with a minimal production of other by-products when glycerol was used as substrate.