Bioenergy maize (FAO, 2008) as well as vegetable

Bioenergy
indicates to sustainable power source generated from biomass. Biomass is any
natural organic material which has the capability to stored sunlight in the
form of chemical energy. Increase in energy consumption and depletion of fossil
fuel reserves has necessitated the demand for alternative energy fuel sources.
Biofuels are another option to petroleum products, which can be utilized alone
or in blend with other petroleum products, for example, petrol. Biofuels are
grouped into in the first, second, third and fourth generation biofuels (Joshi
et al. 2012). First
generation biofuels, which have been chiefly extracted from food and oil crops
including rapeseed oil, sugarcane, sugar beet, and maize (FAO, 2008) as well as vegetable oils and animal fats using
conventional technology (FAO, 2007). It is anticipated that the development in
generation and utilization of biofuels will proceed, but their effects towards
meeting the energy demands will remain limited due to competition with food and
fiber production by using the agricultural land, absence of well managed
agricultural practices and high water and manure requirement. Usually, first
generation biofuels has great impact on global food market and food security
which generated a lot of controversy. This question marks their potential to
replace fossil fuels and sustainability of their production (Moore 2008). The start
of second generation biofuels is projected to produce fuels from the
agricultural residues, forest harvesting residues or wood processing waste (Joshi,,
2012), rather than from food crops. However, the conversion technologies are
not so successful and have not reached the scales for commercial exploitation
which has so far inhibited any significant exploitation.

Conditions
for a technically and economically viable biofuel energy resource are that
(Khosla 2009): it should be competitive in price than petroleum fuels; it should
require non-agricultural land for production; it should help in CO2
sequestration and it should use low water. Biofuels from microalgae may well
meet these conditions and for that reason make a valuable contribution to
achieving the primary energy demand, and at the same time giving environmental
benefits (Wang et al. 2008).

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Microalgae
productivity is high and have faster growth rate as compared to terrestrial
energy crops and can be easily cultivated on non-agricultural land without
giving any competition to food crops and security. As we know, microalgae are
photosynthetic organisms using CO2 for their production, it also
helps in decreasing the greenhouse gases. There are so many species of
microalgae which can grow on fresh, brackish, sea and even in the sewage water.
Microalgae can accumulate approximately up to 60% oil per dry weight of biomass
under such conditions (Chisti, 2007). The algal oil extracted from biomass can
directly be converted into biodiesel which is an environment friendly and also
renewable biofuel (Pandey et al. 2016). In this way, microalgae have gained
attention as a possible producer of biodiesel and offer strong contention as a
favorable feedstock for the production of biodiesel along with other lipid
based biofuels and numerous other byproducts (Wijffels and Barbosa, 2010;
Scott, et al. 2010).

Microalgae also have the ability to produce
different types of renewable fuels that is capable of meeting our future needs
for transportation fuels. These include biodiesel derived from microalgal oil
(Banerjee et al. 2002; Gavrilescu and Chisti, 2005); methane produced by
anaerobic digestion of the algal biomass (Spolaore et al. 2006); and
photobiologically produced biohydrogen (Fedorov et al. 2005; Kapdan and Kargi,
2006). This chapter emphasize on the technologies underneath
microalgae-to-biofuels systems, concentrating on the biomass production,
improvement in algae for increasing yield, processing and the extraction of
biofuels.