Environmental Engineering Reference
In-Depth Information
feedstock for biodiesel (Chisti
2007
). In addition
to lipids and oils, microalgae also contain pro-
teins, carbohydrates, and other nutrients. Hence,
after extraction of the oil from microalgae, the
residual biomass can be used for other utilities
viz., animal feed. A part of the residual biomass
can also be utilized for the production of meth-
ane by anaerobic digestion. The energy generated
from the methane then could further be used in
biodiesel production facility which could lower
the overall production cost of biodiesel (Chisti
2007
). Ekman and Brjesson (
2011
) reported
production of propionic acid by fermentation of
glycerol that was obtained as a by-product from
biodiesel production. A simultaneous production
of biodiesel and bioethanol has been suggested
by Gutierrez et al.
2009
. The palm shell can be
utilized for the production of bioethanol; where-
as, oil from palm seed can be used for production
of biodiesel.
ropsis sp.
; whereas, pigments and biohydrogen
were produced as the coproduct. Nobre et al.
(
2013
) proposed a biorefinery approach for the
feedstock,
Nannochloropsis sp.
wherein, the oil
and pigment was extracted from the microal-
gae. While, oil was utilized for the synthesis of
biodiesel, the left over biomass was utilized for
the production of high value compounds (ca-
rotenoids) and biohydrogen. High lipid content
33 % (w/w) of dried biomass was reported from
the microalgae using supercritical CO
2
extraction
under operating conditions of 40
o
C, 300 bar, and
CO
2
flow rate of 0.62 g/min. The lipid content
was enhanced to 45 % (w/w) of dried biomass
with 70 % recovery of pigments when 20 % (w/w)
ethanol was doped along with supercritical CO
2
.
Biohydrogen was produced by dark fermentation
using
Enterobacter aerogenes
with H
2
yield of
60.6 mL/g dry biomass.
8.2.4
Bioethanol
8.2.2
Biomethane
Fornell et al. (
2013
) reported simultaneous pro-
duction of bioethanol and dimethyl ether from
kraft pulp-mill-based biomass as a biorefinery
approach. It is reported that cost of CO
2
capture
and storage by adopting this method will be low.
Goh and Lee (
2010
) reported that carbohydrate
derived from seaweed that contains hexose sugar
could be fermented to produce bioethanol. Ligno-
cellulosic feedstock is used for the production of
ethanol and dimethyl ester (DME). The conver-
sion efficiency of the raw material to ethanol of
fuel grade is in the range of 30-50 % as estimated
by taking in account the lower heating value. The
low conversion efficiency is attributed to heat
loss and the side reaction that occurs at various
processing steps (Fornell et al.
2013
). Rosen-
berg et al. (
2011
) proposed growing microalgae
in combination with an ethanol biorefinery. The
excess heat from the ethanol biorefinery could be
used to maintain the algal culture at constant tem-
perature in winter seasons. Sequestration of CO
2
released from ethanol biorefinery by microalgae
will lead to reduction in the operating cost by up
to 20 %. Jung et al. (
2013
) reported that the car-
bohydrate content in the macroalgae (seaweed)
Charlton et al.
2009
proposed a green biorefinary
approach utilizing grass as a biomass. The advan-
tages with grass as feedstock are its high digest-
ibility, high sugar, and low lignin. Grass compris-
es cellular material (45 %) and cell wall compo-
nents (55 %). The grass juice has been proposed
to be separated from the lignocellulosic portion
of the grass. Once the liquid from the grass gets
separated, the transport of the fiber will be easier.
The sugar rice juice has been proposed to be fer-
mented on the farm for production of methane
by anaerobic digestion, or for bulk chemical such
as lactic acid. The fiber could be converted to
fermentable sugar using specific enzymes or be
used as animal feed owing to its protein content.
8.2.3
Biohydrogen
Ferreira et al. (
2013
) reported production of bio-
hydrogen from the dark fermentation of leftover
biomass of microalga,
Nannochloropsis sp.
In
the biorefinery approach, biodiesel was produced
as the main product from the oil of
Nannochlo-
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