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Microalga very less cropping area would be

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Microalga includes all unicellular and multicellular
organisms. Prokaryotic microalgae include Cyanobacteria and eukaryotic
microalgae include green algae, red algae and diatoms. Microalgal biodiesel has
a great potential in satisfying the need of today and future use of petroleum.
This is possible due to the round year production and higher yields of algae as
compared to other oil-seed crops like rapeseed, palm oil, jatropha oil, coconut
oil etc. For example: to meet only half the existing transport fuel needs by
biodiesel, would require very large area of cultivation for major oil crops. Table
1 shows the oil content of microalgae. It clearly indicates that oil crops
cannot significantly contribute to replace the petroleum derived fuels in the
near future. This situation can be changed, if microalgae are used for the
production of biodiesel. A very less cropping area would be required for algal
biomass production that satisfies approximately 50% need of the transport fuel
of any country. Table 2 shows the comparison of biodiesel on the basis of crop
type.

                 

Table 1 Oil content of microalgae

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Microalga                            Oil content (% dry weight)

Cylindrotheca
sp.                 16-37

Monallanthus
salina             20

Dunaliella
primolecta           23

Chlorella
sp.                        28-32

Nannochloris
sp.                  20-35

Nitzschia
sp.                                    45-47

Schizochytrium
sp.                50-77

(Source: Chisti, 2007)

 

Table 2 Oil yields based on Crop type (Source:
Chisti, 2007)

Crop                       Oil Yield (L/ha)             Land area needed (M ha)

Oil palm                  5950                             45

Coconut                  2689                             99

Jatropha                  1892                             140

Canola                    1190                             223

Soybean                  446                               594

Corn                       172                               1540

Microalgae (30 % oil dry wt. basis)                                                                                        136900                          2

Microalgae (70% oil dry wt.
basis)                                                                                         58700                           4.5

(Source: Chisti, 2007)

 

In view of this, microalgal biomass would be the only source
for biodiesel which have the potential to completely replace the fossil fuel.
Microalgae are capable of production all the year, therefore oil production
from microalgae exceeds from the other oil-seed crops. For example: Biodiesel
yield from open ponds is 12000 Lha-1 as compared to 11901 Lha-1 for rapeseed
(Schenk et al. 2008). Microalgae grow in liquid media and need less water than
other terrestrial crops, thereby reducing burden on fresh water sources
(Dismukes et al. 2008). Microalgae can be cultivated in non-agricultural land,
and thereby providing no challenge to food crops and food security. Microalgae
have fast growth rate and double their biomass within 24 h and sometimes during
exponential growth as short as 3.5 h. Many of the species have oil content in
the range of 30-80% dry weight of biomass and can exceed 80% by weight of dry
biomass (Spolaore et al. 2006). Also microalgae help in fixing CO2
from the atmosphere and thereby reducing the green-house gases. Nutrients used
for microalgae cultivation can be obtained from the waste water released from
agro-food industries and thereby helps in waste water treatment. Algal biomass
can also be used as feed or as a fertilizer for crops and along with this it can
also produce co-products such as proteins (Guschina and Harwood, 2006).
Microalgae doesn’t not require any pesticide or herbicide application (Rodolfi
et al. 2008). It has the potential to increase the oil yield significantly by
varying the growth conditions. Microalgae capable of producing bio-hydrogen
photo-biologically (Ghirardi et al. 2000).

These above combination of biodiesel production, fixation of
CO2, biological treatment of waste water, bio-hydrogen production, ethanol and
methane production underscore the potential of microalgae. Despite these
potentials of microalgae, many challenges have slowed the development of algal
biofuel technology to commercial form. There should not be a single strain till
now developed which is capable of producing biodiesel in great quantities
(Brennan and Owende, 2009). Lacking of techniques for CO2 diffusion
losses and attaining higher photosynthetic efficiencies (Ugwu et al. 2008).
There are very few commercial plants in production area, therefore lack of data
for large scale plants (Pulz et al. 2001).

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