amylases, whereas sugar-based crops only require direct extraction of fermentable
sugar. Thus, the sugar-based ethanol is cheap as compared to starch-based technique.
However, the limitation associated with the sugar-based ethanol generation is that
the sugar crops require specific climate and soil type for their growth and thus cannot
be cultivated around the globe (Barcelos et al. 2011).
Starch-based ethanol production from corn primarily utilizes dry grinding or wet
milling method. Dry grinding method involves the following steps: (i) slurry preparation by mixing corn flour with water, (ii) cooking of the slurry, (iii) liquefaction
using thermostable alpha amylase, (iv) saccharification using glucoamylase,
(vi) ethanol fermentation, and (vii) distillation. After ethanol fermentation broth is
subjected to distillation, leaving the solid fraction, thick and thin stillage. The thick
stillage syrup mixed with the solid fraction is used as animal feed, whereas the thin
stillage is recycled for water recovery. During the wet milling process, the biomass is
first grounded followed by its separation from individual components, and the starch
obtained is subjected to wet milling. The later stage of the process is similar to the
dry grinding. Different co-products are generated in dry grinding and wet milling
which can contribute to overall economy of the process. The dry grinding of corn
gives ethanol yield of 0.395 L/kg which is slightly higher to 0.372 L/kg as obtained
from wet milling method (Shapouri et al. 2002). Commercially, dry grinding method
is more preferred because the wet milling method is costly and equipment is
expensive. In the USA, 70–86% ethanol from corn is produced using dry grinding
method (Mosier and Ileleji 2015). A summary of different pretreatment and fermentation methods used for bioethanol production using various starch-based feedstocks
is summarized in Table 7.3.
7.3.7.1.2 Bioethanol Production Using Sugar-Based Feedstock
After the USA corn-based ethanol, Brazilian sugar-based ethanol is the second
largest ethanol in the world. Sugarcane-based ethanol generation involves different
steps: (i) extraction of juice from the sugarcane or beet sugar using roller press;
(ii) purification of sugar using lime (calcium hydroxide) or calcium saccharate which
reduces colorants and neutralize organic acids; (iii) filtration, that remove debris
from juice which are collected as filter cake, (v) evaporation or condensation
(14–18% sugar level, i.e., sugar tolerance capacity of microbes), and
(vi) fermentation of the condensed syrup under sterilized condition at appropriate
temperature and pH (Vohra et al. 2014). Additionally, nitrogenous source is also
added to minimize osmotic stress due to high sugar content. The by-products
majorly bagasse and filter cake obtained after the extraction of juice and filtration
step can be used for different purposes. The generation of heat and electricity from
bagasse can also help in minimizing the overall cost of production of ethanol.
Bagasse can also be used as substrate for production of 2G bioethanol. The filter
cakes are used as eco-friendly fertilizers (Zabed et al. 2017). A summary of different
pretreatment and fermentation methods used for bioethanol production using various
starch-based feedstocks is summarized in Table 7.3.
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B. Kumar et al.
sugar. Thus, the sugar-based ethanol is cheap as compared to starch-based technique.
However, the limitation associated with the sugar-based ethanol generation is that
the sugar crops require specific climate and soil type for their growth and thus cannot
be cultivated around the globe (Barcelos et al. 2011).
Starch-based ethanol production from corn primarily utilizes dry grinding or wet
milling method. Dry grinding method involves the following steps: (i) slurry preparation by mixing corn flour with water, (ii) cooking of the slurry, (iii) liquefaction
using thermostable alpha amylase, (iv) saccharification using glucoamylase,
(vi) ethanol fermentation, and (vii) distillation. After ethanol fermentation broth is
subjected to distillation, leaving the solid fraction, thick and thin stillage. The thick
stillage syrup mixed with the solid fraction is used as animal feed, whereas the thin
stillage is recycled for water recovery. During the wet milling process, the biomass is
first grounded followed by its separation from individual components, and the starch
obtained is subjected to wet milling. The later stage of the process is similar to the
dry grinding. Different co-products are generated in dry grinding and wet milling
which can contribute to overall economy of the process. The dry grinding of corn
gives ethanol yield of 0.395 L/kg which is slightly higher to 0.372 L/kg as obtained
from wet milling method (Shapouri et al. 2002). Commercially, dry grinding method
is more preferred because the wet milling method is costly and equipment is
expensive. In the USA, 70–86% ethanol from corn is produced using dry grinding
method (Mosier and Ileleji 2015). A summary of different pretreatment and fermentation methods used for bioethanol production using various starch-based feedstocks
is summarized in Table 7.3.
7.3.7.1.2 Bioethanol Production Using Sugar-Based Feedstock
After the USA corn-based ethanol, Brazilian sugar-based ethanol is the second
largest ethanol in the world. Sugarcane-based ethanol generation involves different
steps: (i) extraction of juice from the sugarcane or beet sugar using roller press;
(ii) purification of sugar using lime (calcium hydroxide) or calcium saccharate which
reduces colorants and neutralize organic acids; (iii) filtration, that remove debris
from juice which are collected as filter cake, (v) evaporation or condensation
(14–18% sugar level, i.e., sugar tolerance capacity of microbes), and
(vi) fermentation of the condensed syrup under sterilized condition at appropriate
temperature and pH (Vohra et al. 2014). Additionally, nitrogenous source is also
added to minimize osmotic stress due to high sugar content. The by-products
majorly bagasse and filter cake obtained after the extraction of juice and filtration
step can be used for different purposes. The generation of heat and electricity from
bagasse can also help in minimizing the overall cost of production of ethanol.
Bagasse can also be used as substrate for production of 2G bioethanol. The filter
cakes are used as eco-friendly fertilizers (Zabed et al. 2017). A summary of different
pretreatment and fermentation methods used for bioethanol production using various
starch-based feedstocks is summarized in Table 7.3.
178
B. Kumar et al.