Environmental Engineering Reference
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second generation feedstock for biofuel. The sec-
ond generation feedstock included nonfood bio-
mass of lignocellulosic materials viz., bagasse,
stover from sugar, forest and crop residues, mu-
nicipal solid wastes, vegetative grass, and short
rotation forest crops. The second generation
feedstock provided oil from the plant seeds and
the lignocellulosic material present in the residue
of the seeds after oil extraction was used for the
synthesis of bioethanol. Microalgae have been
considered as a third generation feedstock for
biofuels as they grow in water and thus do not
compete with the land based food crops. Biohy-
drogen and bioelectricity has recently been ex-
plored as a fourth generation feedstock (Sharma
et al.
2011
). At present, the common biofuels pro-
duced in the world today are biodiesel, bioetha-
nol, and biogas (comprising methane) (Cherubini
and Ulgiati
2010
). International Energy Agency
(IEA) estimates that biofuels will fulfill 27 % of
global energy demand in the transport sector in
2050 due to its growing interest and popularity
(Fornell et al.
2013
).
To mitigate the climate change and to enhance
the energy security along with maintaining sus-
tainability has led to exploration of biorefinery
concept (Cherubini and Ulgiati
2010
). A biorefin-
ery approach integrates multifunctional process,
as various material products of utility and energy
are coproduced simultaneously (Cherubini et al.
2011
). As per the definition of IEA Bioenergy
Task 42 “
Biorefining is the sustainable process-
ing of biomass into a spectrum of marketable
products and energy
.” A wide range of technolo-
gies separate biomass (viz., wood, grasses, corn)
from useful products (protein, carbohydrate, and
lipids) which, depending on their suitability, can
thereafter be converted to value added products,
biofuels, and chemicals. The biobased products
that are already in the market include starch,
oil, cellulose, and chemicals (lactic acid, amino
acids). A variety of other compounds that are also
derived from biomass include adhesives, clean-
ing compounds, detergents, dielectric fluids,
dyes, hydraulic fluids, inks, lubricants, packag-
ing materials, paints and coatings, paper and box
board, plastic fillers, polymers, solvents, and sor-
bents. However, the biofuels and biochemicals
are usually produced independently as a single
chain product that results in their competition
with the food and feed industry. A biorefinery
based on lignocellulosic feedstock can produce
large biomass as the whole crop is available as
compared to only a part with the conventional
crops (Cherubini
2010
). In a biorefinery, the con-
sumption of nonrenewable energy is minimized
and the complete and efficient use of biomass
gets maximized (Cherubini
2010
). The advan-
tages of biofuels over the conventional fossil
fuels are: renewability, CO
2
sequestration, envi-
ronmental friendly and biodegradability, and sus-
tainability. According to the National Renewable
Energy Laboratory, a biorefinery is defined as “
a
facility that integrates conversion processes and
equipment to produce fuels, power, and chemi-
cals from biomass
.” The integrated biorefinery
approach could produce fuels as well as platform
chemicals, and thus could complement the petro-
leum industry and refineries.
Cherubini (
2010
) stated that bio-industries
can combine their material flows for a complete
utilization of all biomass components. This resi-
due from one bioindustry can be utilized as an
input for the other bio-industry. As an example,
lignin from a lignocellulosic ethanol production
plant becomes an input for other industries, giv-
ing rise to integrated bio-industrial systems. As
biomass resources are locally available, their use
may contribute to reduce dependence on fossil
fuels. In a biorefinery approach, a continuous
supply of feedstock is maintained as the feed-
stock comes from various sources of crops viz.,
agriculture, forestry, and industrial activities. The
biomass feedstock is grouped in the following
category: carbohydrates and lignin, triglycerides,
and mixed organic residues (Cherubini
2010
).
As microalgae comprises a variety of constit-
uents (lipids, proteins, and carbohydrates), these
substrates has the potential to serve products
for different markets (Koopmans et al.
2013
).
Among the various constituents, lipids and pro-
teins are the largest fraction present in the mi-
croalgae. While, lipids can be utilized for the
production of biofuel, the proteins may be puri-
fied and utilized as food, feed, health, and bulk
chemical market. The carbohydrates (starch and
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