Environmental Engineering Reference
In-Depth Information
could be diverted to utilization in a biorefinery.
As macroalgae contain low amount of lignin,
they can be a better substrate in the production
of various utility products in a biorefinery. Un-
like microalgae, the macroalgae has a low protein
content (7-15 % dry wt.) and lipid content (1-5 %
dry wt.). The microalgae possess a comparative-
ly high content of protein and lipid of 40-60 %
dry wt. and 10-20 % dry wt. respectively. This
is due to high water and alkali metal content of
70-90 % fresh wt. and 10-50 % dry wt. respec-
tively in macroalgae (Jung et al.
2013
). Goh and
Lee (
2010
) utilized a macroalgae (seaweed) for
the production of bioethanol. The carbohydrate
content in the seaweed present as hexose sugars
was utilized for the production of bioethanol.
Luo et al. (
2011
) proposed complete utiliza-
tion of rapeseed plant (seed and straw) for the
production of biofuels (biodiesel and bioetha-
nol) as a biorefinery concept. Using straw as the
feedstock, a bioethanol yield of 0.15 g ethanol/g
dry straw was obtained with pretreatment with
alkaline peroxide and stream. The coproducts
and by-products obtained as rapeseed cake, glyc-
erol, hydrolysate, and stillage were utilized for
production of methane and mixture of hydrogen
and methane. The energy recovery process that
was only 20 % with the production of conven-
tional biodiesel increased to 60 % by adopting the
biorefinery approach that produced bioethanol,
biohydrogen, and methane along with biodiesel.
Lohrasbi et al. (
2010
) described the economic
feasibility of a biorefinery from citrus waste. On
hydrolysis by dilute sulfuric acid, the citrus waste
can be converted to limonene, ethanol, and bio-
gas. The total cost estimated for the production
of ethanol was 0.91 USD/L with the production
capacity of 100,000 tons/year inclusive of the
transportation and handling cost. The production
of limestone and biogas (methane) along with
enhancement of plant capacity could reduce the
production cost of ethanol to 0.46 USD/L which
makes the process economical and sustainable.
The lignin present in the lignocellulosic bio-
mass is not easily degraded, hence needs ex-
pensive pretreatment. Plant genetic engineering
technology can lead to lower the cost of produc-
tion of biofuel from lignocellulosic materials.
Recent advancements in research have led to new
opportunities in manipulation of lignin for devel-
opment of biofuel. The cell degrading enzymes
that include cellulases and hemicellulases could
be produced in the crop biomass itself (Menon
and Rao
2012
).
8.3
Environmental Impact of
Microalgal Biorefinery
8.3.1
Water Footprint (WF)
The sustainability of a biofuel can be measured
in terms of its ecological footprint. Water, as a
scarce commodity, can be a limiting factor for
cultivation of energy crops. WF measures the
water use intensity of a nation. It is estimated
that the water requirement for the production of
primary energy from biomass is two to threefold
greater than that required from the fossil fuel
(Tan et al.
2009
). WF is an indicator of direct as
well as indirect usage of freshwater. Gerbens-
Leenes et al. (
2012
) reports that by 2030, the
global blue biofuel WF would have grown to
5.5 % of the total blue water available for human
consumption thus creating pressure on freshwa-
ter resources. A significant amount of global WF
(86 %) is attributed to agriculture. Any increase
in diversion of the biomass for development of
energy will require additional load on the water
that may lead to water shortages. The WF can be
reduced by utilizing multiple feedstocks for pro-
duction of biofuel. IEA estimated that the energy
use attributed to biomass will increase to 71 EJ in
2030. The production of biocrops for bioethanol
and biodiesel will require large amount of fresh-
water that includes both green water (precipita-
tion water) and blue water (irrigation water from
ground and surface water) (Gerbens-Leenes et al.
2012
). Hence, biorefinery approach is expected
to minimize the WF of biofuels.
Batan et al. (
2013
) estimated the WF of a
closed photo-bioreactor based biofuel and as-
sessed the WF on the basis of blue, green, and
lifecycle WF. Blue WF comprised of the water
directly used for cultivation and process needs
for both consumptive and nonconsumptive use.
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