Liquid biofuels are suitable for use as an alternative to
fossil fuels. Renewable biofuels can be used as a replacement of fossil fuels only if: (a) the global food-supply chain
is not compromised, (b) the carbon-energy balance is neutral
(C-neutral fuel) or negative (C-negative fuel), and (c) these
are environment-friendly. C-negative fuels are expected to
decrease the atmospheric carbon concentration and C-neutral
fuels are the ones that have no effect on the atmospheric
carbon concentration (Johnson et al. 2007). Among the
biofuels, bioethanol is considered a potential transportation
biofuel. Bioethanol is known to have an 80% lower emission
profile when compared to the conventional petro-gasoline
(Akbas and Stark 2016).
Choice of substrate: The choice of substrate for bioethanol production plays a significant role in the overall
economics of the process. Among agricultural biomasses,
different food wastes for bioethanol production are being
explored worldwide, some of which are potato peels, potatoprocessing wastes, pineapple peels, whey, rice husks, coffeebean husks, corn-processing wastes, and fruit-processing
wastes. Food-waste utilization for bioethanol production
provides sustainability as well as reduces solid-disposal
liability (Gonzales et al. 2005; Pires et al. 2011).
1G biofuels are considered to be the ones that are derived
from energy-intensive substrates like starch-based crops,
sugarcane molasses, and many other crops. The dependency
on starch-based crops for biofuels production creates food
competency and stress on farmlands. 2G biofuels are those
which are produced from lignocellulosic-based substrates,
mainly from agricultural wastes. Other lignocellulosic biomasses include organic wastes from municipalities and
industries (Akbas and Stark 2016). The utilization of organic
wastes for biofuel production is one of the strategies to
ensure food security, and waste management along with
minimizing environmental pollution (Stephen and Periyasamy 2018).
2 Utilization of Food Wastes for Bioethanol
Production
As the population is increasing steadily, the demand for food
production is expected to rise as well. Solid wastes from the
food industries are either dumped into landfills causing
environmental pollution or fed as an animal fodder. For
example, out of the wastes generated from the Indian-grain
processing industries, 90% is discarded and only 10% is
utilized as an animal fodder (Akbas and Stark 2016). Data
indicate that 55% of food wastage comes from fresh fruits
and vegetables, dairy products, and the rest is due to wastage
of grain products and fats and oils [U.S. Department of
Agriculture]. Different food wastes are generated by the
industries which have the scope of utilization for biofuel
production, like sugarcane residues, citrus wastes, molasses,
residues from starch-based foods, and so on. Their utilization
thus provides dual benefits, concerning economics and waste
management with zero or low cost of substrate (waste)
procurement. The food wastes are a supplement to the biologically derived ethanol. Table 1 indicates different food
wastes, fermenting organisms, and fermentation strategies
involved in bioethanol production.
3 Whey and Lignocellulosic-Based Biomass
The main difference between lignocellulosic and
pectin-based biomasses lies in the availability of predominant lignin content present in the former while being absent
in the latter. The wastes from fruits industries have a negligible amount of lignin content in them; for example, the
lignin content is less than 2% (dry wt. basis) in citrus wastes
and sugar-beet pulp when compared against 26% (dry wt.
basis) present in Monterey pine (Edwards and
Doran-Peterson 2012). Lignin present in lignocellulosic
biomasses hinders the pretreatment step, and thus affects the
efficiency of the enzymatic degradation process (Chang and
Holtzapple 2000; Guo et al. 2009). The compositional
analysis of lignocellulosic biomasses suggests that cellulose
present is 25–55%, hemicellulose 24–50%, and lignin is
present in the range of 10–35% (all on dry wt. basis) (Sun
and Cheng 2002). Linkage of cellulose with hemicellulose is
just a physical association, whereas there is a chemical
linkage of cellulose with lignin (Mussatto et al. 2008).
Cellulose is bonded with hemicellulose as microfibrils to
form a matrix layered with lignin fractions over it (Rubin
2008). The lignocellulosic biomasses need pretreatment
(physical, chemical, or biological) prior to fermentation for
lignin separation and/or its effective particle size reduction.
Economics of the process show that more than 50% of the
total operating cost arises because of the pretreatment for
lignin degradation. The choice of the pretreatment technique
has a pervasive influence on all factors concerning the
degradation of cellulosic materials (Yang and Wyman
2008).
Pectin-rich biomass, as the name suggests, is predominant
in pectin content, varying from 12 to 35% (dry wt. basis) of
the biomass. The main advantage of using pectin-rich biomasses lies in the ease of hydrolysis, as these biomasses are
a processed residue discarded from the processing of fruits or
vegetables for sugar or juice production. A study on this
class of biomasses by different research groups revealed that
these do not require harsh pretreatment techniques, as
required otherwise by lignocellulosic-rich biomasses. Citrus
wastes, one of the abundant pectin-rich biomasses, require
pretreatment for limonene separation which is inhibitory
toward fermentation and also for the biomass-structure
46
N. Dey and A. N. Bhaskarwar
fossil fuels. Renewable biofuels can be used as a replacement of fossil fuels only if: (a) the global food-supply chain
is not compromised, (b) the carbon-energy balance is neutral
(C-neutral fuel) or negative (C-negative fuel), and (c) these
are environment-friendly. C-negative fuels are expected to
decrease the atmospheric carbon concentration and C-neutral
fuels are the ones that have no effect on the atmospheric
carbon concentration (Johnson et al. 2007). Among the
biofuels, bioethanol is considered a potential transportation
biofuel. Bioethanol is known to have an 80% lower emission
profile when compared to the conventional petro-gasoline
(Akbas and Stark 2016).
Choice of substrate: The choice of substrate for bioethanol production plays a significant role in the overall
economics of the process. Among agricultural biomasses,
different food wastes for bioethanol production are being
explored worldwide, some of which are potato peels, potatoprocessing wastes, pineapple peels, whey, rice husks, coffeebean husks, corn-processing wastes, and fruit-processing
wastes. Food-waste utilization for bioethanol production
provides sustainability as well as reduces solid-disposal
liability (Gonzales et al. 2005; Pires et al. 2011).
1G biofuels are considered to be the ones that are derived
from energy-intensive substrates like starch-based crops,
sugarcane molasses, and many other crops. The dependency
on starch-based crops for biofuels production creates food
competency and stress on farmlands. 2G biofuels are those
which are produced from lignocellulosic-based substrates,
mainly from agricultural wastes. Other lignocellulosic biomasses include organic wastes from municipalities and
industries (Akbas and Stark 2016). The utilization of organic
wastes for biofuel production is one of the strategies to
ensure food security, and waste management along with
minimizing environmental pollution (Stephen and Periyasamy 2018).
2 Utilization of Food Wastes for Bioethanol
Production
As the population is increasing steadily, the demand for food
production is expected to rise as well. Solid wastes from the
food industries are either dumped into landfills causing
environmental pollution or fed as an animal fodder. For
example, out of the wastes generated from the Indian-grain
processing industries, 90% is discarded and only 10% is
utilized as an animal fodder (Akbas and Stark 2016). Data
indicate that 55% of food wastage comes from fresh fruits
and vegetables, dairy products, and the rest is due to wastage
of grain products and fats and oils [U.S. Department of
Agriculture]. Different food wastes are generated by the
industries which have the scope of utilization for biofuel
production, like sugarcane residues, citrus wastes, molasses,
residues from starch-based foods, and so on. Their utilization
thus provides dual benefits, concerning economics and waste
management with zero or low cost of substrate (waste)
procurement. The food wastes are a supplement to the biologically derived ethanol. Table 1 indicates different food
wastes, fermenting organisms, and fermentation strategies
involved in bioethanol production.
3 Whey and Lignocellulosic-Based Biomass
The main difference between lignocellulosic and
pectin-based biomasses lies in the availability of predominant lignin content present in the former while being absent
in the latter. The wastes from fruits industries have a negligible amount of lignin content in them; for example, the
lignin content is less than 2% (dry wt. basis) in citrus wastes
and sugar-beet pulp when compared against 26% (dry wt.
basis) present in Monterey pine (Edwards and
Doran-Peterson 2012). Lignin present in lignocellulosic
biomasses hinders the pretreatment step, and thus affects the
efficiency of the enzymatic degradation process (Chang and
Holtzapple 2000; Guo et al. 2009). The compositional
analysis of lignocellulosic biomasses suggests that cellulose
present is 25–55%, hemicellulose 24–50%, and lignin is
present in the range of 10–35% (all on dry wt. basis) (Sun
and Cheng 2002). Linkage of cellulose with hemicellulose is
just a physical association, whereas there is a chemical
linkage of cellulose with lignin (Mussatto et al. 2008).
Cellulose is bonded with hemicellulose as microfibrils to
form a matrix layered with lignin fractions over it (Rubin
2008). The lignocellulosic biomasses need pretreatment
(physical, chemical, or biological) prior to fermentation for
lignin separation and/or its effective particle size reduction.
Economics of the process show that more than 50% of the
total operating cost arises because of the pretreatment for
lignin degradation. The choice of the pretreatment technique
has a pervasive influence on all factors concerning the
degradation of cellulosic materials (Yang and Wyman
2008).
Pectin-rich biomass, as the name suggests, is predominant
in pectin content, varying from 12 to 35% (dry wt. basis) of
the biomass. The main advantage of using pectin-rich biomasses lies in the ease of hydrolysis, as these biomasses are
a processed residue discarded from the processing of fruits or
vegetables for sugar or juice production. A study on this
class of biomasses by different research groups revealed that
these do not require harsh pretreatment techniques, as
required otherwise by lignocellulosic-rich biomasses. Citrus
wastes, one of the abundant pectin-rich biomasses, require
pretreatment for limonene separation which is inhibitory
toward fermentation and also for the biomass-structure
46
N. Dey and A. N. Bhaskarwar