Environmental Engineering Reference
In-Depth Information
triacylglycerols (TAG) within their cell mass, which could be as high as 30 % of
their cell weight. These lipids can serve as feedstock for producing biodiesel and
green diesel. Algal resources offer several advantages such as it can capture 10 % of
sunlight as compared to 0.5 % by terrestrial plant, require less land area, can be
converted to liquid fuels using simpler technology than those required for cellulose
conversion, and have secondary uses which fossil fuel does not have. Additionally,
it also reduces anthropogenic pollutants to the environment. Algal biodiesel can
easily be used in unmodi
cant advantages over
conventional diesel fuel because it is renewable and biodegradable and might
produce lower emissions of sulfur oxides and particulates when burned. Though the
life cycle assessment (LCA) of algal biofuels suggests that at present, it is not so
attractive economically, they are environmentally better than the fossil fuels.
Several biotechnological strategies have been adopted to increase the lipid content
of the algal biomass, such as metabolic engineering and bioprocess modi
ed diesel engines, and it has signi
cation
and mixed culture cultivation. For large-scale cultivation, the pond system offers
simplicity in operation, lower capital, and recurring expenditure but has issues of
harvesting and control of contamination. Various photobioreactors have been
developed which offer potential bene
ts to control the problems of pond system,
but these require high-energy input for operation, which makes them economically
unattractive presently.
2.4 Biohydrogen
Among other alternative energy sources, biohydrogen could be regarded as the most
promising future energy carrier as is expected to contribute substantially for the
future energy needs. Biohydrogen is recognized as clean energy carrier as it pro-
duces only water when combusted. It has a high calori
c value (122 kJ/mol) of any
known fuels which is 5 and 2.6 times greater than ethanol and gasoline, respectively,
which offers a crosscut from electricity to transportation fuels and energy storage. In
context of energy generation per unit mass, it has a great potential to be developed as
an alternative fuel in the near future (Sabariswaran et al.
2013
). Hydrogen has a high
low heating value (LHV) and can be used in fuel cells and internal combustion
engines. Worldwide, the compound annual growth rate of quantitative hydrogen
production was estimated to grow by 5.6 % during the period 2011
2016 and the
global market for hydrogen generation would mature from estimated $87.5 billion in
2011 to $118 billion by 2016 with a CAGR of 6.2 % (
http://articles.pubarticles.com/
3076864,561523.html
as on June 25, 2014).
Biohydrogen production is one among the most promising future energy sources
which is expected to contribute substantially for the future energy needs for the
mankind. It is unfortunate that only 5 % production from renewable sources has
been achieved yet. Four mechanisms are known for biohydrogen production: direct
biophotolysis, indirect biophotolysis, dark fermentation, and photo fermentation.
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