negatively affecting the ethanol yield. This effect of osmotic stress can be reduced to
supplementing different nitrogenous and fat containing components such as ammonium ions (Laopaiboon et al. 2009), oil seed meal (Sankh et al. 2011), soya flour
(Xiao et al. 2010), urea (Pradeep and Reddy 2010), and yeast extract (Chang et al.
2011), etc. which release free amino nitrogen or fatty acid-enhancing cell growth and
viability (Kawa-Rygielska and Pietrzak 2014).
7.3.3.3 Integration of Saccharification and Fermentation for Enhanced
Bioethanol Production
The ethanol generation from different biomasses involves several steps. In order to
minimize the capital and operational cost, there is a need to minimize the steps
involved in biomass to production of bioethanol. The key process, i.e., hydrolysis
and fermentation, is usually performed separately. 1G and 2G biomass are rich in
cellulose, so separate hydrolysis of cellulose followed by fermentation of hydrolyzed
sample is usually performed. In commercial bioethanol production from lignocellulosic biomass, different strategies were followed for hydrolysis and fermentation of
cellulosic and hemicellulosic component.
7.3.3.3.1 Separate Hydrolysis and Fermentation Process (SHF) for Bioethanol
Production
It is a three-step process where joint liquid obtained from hemicelluloses and
cellulose hydrolysis reactors is first passed to hexose fermentation reactors; the
broth from this reactor is distilled for ethanol generation. The leftover broth
containing xylose and other pentose passed through pentose’s reactor and converted
to ethanol using pentose-utilizing ethanologenic microbes followed by distillation
(Hamelinck et al. 2005).
7.3.3.3.2 Separate Hydrolysis and Co-fermentation (SHCF) for Bioethanol
Production
Further development reduced saccharification and fermentation to two-step process
where hemicellulose and cellulose hydrolyzed separately and fermentation of both
hexoses and pentoses was carried out in the same reactors called as separate
hydrolysis and co-fermentation(SHCF) process (Girio et al. 2010). In SHF and
SHCF process, the hydrolysis of cellulose and hemicelluloses can lead to accumulation of sugars that can inhibit the enzymatic action of hydrolyzing enzyme, thus
causing incomplete breakdown of carbohydrate polymer (Mojović et al. 2006).
When the complete hydrolysate is transferred to fermenter, the high sugar content
in broth may cause osmotic stress to yeast, thus causing decrease in final bioethanol
yield (Nikolić et al. 2010)
7.3.3.3.3 Simultaneous Saccharification and Fermentation (SSF)
for Bioethanol Production
The osmotic stress and end product’s inhibitory effect can be countered by a novel
method of simultaneous saccharification and fermentation. Currently, SSF is the
most sought-after technique at both laboratory and industrial scale where both
7 Bioethanol Production: Generation-Based Comparative Status Measurements
173
supplementing different nitrogenous and fat containing components such as ammonium ions (Laopaiboon et al. 2009), oil seed meal (Sankh et al. 2011), soya flour
(Xiao et al. 2010), urea (Pradeep and Reddy 2010), and yeast extract (Chang et al.
2011), etc. which release free amino nitrogen or fatty acid-enhancing cell growth and
viability (Kawa-Rygielska and Pietrzak 2014).
7.3.3.3 Integration of Saccharification and Fermentation for Enhanced
Bioethanol Production
The ethanol generation from different biomasses involves several steps. In order to
minimize the capital and operational cost, there is a need to minimize the steps
involved in biomass to production of bioethanol. The key process, i.e., hydrolysis
and fermentation, is usually performed separately. 1G and 2G biomass are rich in
cellulose, so separate hydrolysis of cellulose followed by fermentation of hydrolyzed
sample is usually performed. In commercial bioethanol production from lignocellulosic biomass, different strategies were followed for hydrolysis and fermentation of
cellulosic and hemicellulosic component.
7.3.3.3.1 Separate Hydrolysis and Fermentation Process (SHF) for Bioethanol
Production
It is a three-step process where joint liquid obtained from hemicelluloses and
cellulose hydrolysis reactors is first passed to hexose fermentation reactors; the
broth from this reactor is distilled for ethanol generation. The leftover broth
containing xylose and other pentose passed through pentose’s reactor and converted
to ethanol using pentose-utilizing ethanologenic microbes followed by distillation
(Hamelinck et al. 2005).
7.3.3.3.2 Separate Hydrolysis and Co-fermentation (SHCF) for Bioethanol
Production
Further development reduced saccharification and fermentation to two-step process
where hemicellulose and cellulose hydrolyzed separately and fermentation of both
hexoses and pentoses was carried out in the same reactors called as separate
hydrolysis and co-fermentation(SHCF) process (Girio et al. 2010). In SHF and
SHCF process, the hydrolysis of cellulose and hemicelluloses can lead to accumulation of sugars that can inhibit the enzymatic action of hydrolyzing enzyme, thus
causing incomplete breakdown of carbohydrate polymer (Mojović et al. 2006).
When the complete hydrolysate is transferred to fermenter, the high sugar content
in broth may cause osmotic stress to yeast, thus causing decrease in final bioethanol
yield (Nikolić et al. 2010)
7.3.3.3.3 Simultaneous Saccharification and Fermentation (SSF)
for Bioethanol Production
The osmotic stress and end product’s inhibitory effect can be countered by a novel
method of simultaneous saccharification and fermentation. Currently, SSF is the
most sought-after technique at both laboratory and industrial scale where both
7 Bioethanol Production: Generation-Based Comparative Status Measurements
173