Environmental Engineering Reference
In-Depth Information
glycogen present in cytoplasm; and cellulose in
the inner cell wall) of microalgae can be utilized
in the production of ethanol and chemicals. The
cultivation of microalgae only for production of
biofuel is cost intensive. The cost incurred during
cultivation is due to colossal water requirement.
Also, the downstream processing requires sub-
stantial production cost. Thus, various products
can be derived from a single source of feedstock
(Koopmans et al.
2013
). The carbohydrate from
microalgae could be utilized for the production of
ethanol and chemicals. However, the techniques
that could be applied for a biorefinery will vary
according to the species selected. Some of the
microalgae species do not have a cell wall which
makes the cell disruption technique less energy
intensive. The microalgal cell usually consists of
lysosomes, mitochondria, and endoplasmic re-
ticulum. It is more practical to disrupt the cells to
release lipids, proteins, and carbohydrates from
the cytoplasm and later fractionates the larger
cell compartments (organelles) to obtain specific
compounds (Koopmans et al.
2013
).
Though there exists a vast reserve of oil
amounting 90 billion (bn) barrels in Arctic re-
gion, environmental issues will be a major con-
straint for their accessibility. Nevertheless, the
fossil fuel reserves are finite and nonrenewable.
National Renewable Energy Laboratory defines
“biorefinery” as a facility that can integrate bio-
mass conversion process and equipment for the
production of a variety of utility products from
biomass viz., fuels, power, and chemicals (Charl-
ton et al.
2009
). Charlton et al.
2009
reports that
in order to make a biorefinery sustainable, the
whole plant along with its fibrous fraction should
be utilized as feedstock. In the first generation
process, microbes are used to transform readily
fermentable sugars and starch. In the second gen-
eration process, the “locked-up” sugar and other
molecules in the lignocellulosic fraction are also
utilized. The novel technologies include steam,
acid, alkali, and enzymatic processes to produce
fermentable sugars which can then further be
utilized as substrate for production of various
chemicals. The integrated approach in a biore-
finery, thus, could provide a range of useful end
products viz., biofuels (e.g., biodiesel, bioetha-
nol), other energy sources (syngas and bio-oil),
pharmaceutical products (e.g., cancer drugs), and
commercially important platform chemicals (or-
ganic acids) (Charlton et al.
2009
). Among the
feedstocks, grass can be utilized as a low cost
material to obtain high value products. Hence,
the biorefinery extracts the maximum value
from the biomass by the production of a variety
of valuable products and make the overall pro-
cess sustainable as well as economically viable.
Combined production of biofuel and generation
of heat makes biorefinery an attractive opera-
tion. The biorefinery market utilizing the entire
biomass is estimated to reach US$ 295 billion
by 2020 (Hernandez et al.
2013
). The products
from the biorefinery has the potential to replace
compounds that are chemically identical (ethyl-
ene from bioethanol could replace ethylene ob-
tained from natural gas) and those with similar
functionality (Hernandez et al.
2013
). In biore-
fineries, high value products (biofuels, specialty
chemicals, pharmaceuticals) could be derived.
An integrated processes viz., digestion, fermen-
tation, pyrolysis, gasification, results in enhance-
ment of energy efficiency and material recovery
(Ng
2010
).
8.2
A Biorefinery Approach for
Production of Biofuels
The term biofuel is referred to soild, liquid, or
gaseous fuel that is obtained from biorenewable
feedstocks. The biorefinery concept is applied to
biomass in a similar way as that is adopted in re-
fining of petroleum where a variety of products
are obtained. Hence, biorefineries simultaneous-
ly produce biofuels, bio-based chemicals, heat,
and power.
8.2.1
Biodiesel
Biodiesel that is derived from the oil from crops,
waste cooking oil, or animal fats is unable to
fulfill the demand for the transport fuel as it is
required in bulk amount. It is envisaged that mi-
croalgae has the potential to fulfill the demand of
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