Microalga very less cropping area would be

Microalga includes all unicellular and multicellularorganisms.

Prokaryotic microalgae include Cyanobacteria and eukaryoticmicroalgae include green algae, red algae and diatoms. Microalgal biodiesel hasa 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 ascompared to other oil-seed crops like rapeseed, palm oil, jatropha oil, coconutoil etc. For example: to meet only half the existing transport fuel needs bybiodiesel, would require very large area of cultivation for major oil crops. Table1 shows the oil content of microalgae.

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It clearly indicates that oil cropscannot significantly contribute to replace the petroleum derived fuels in thenear future. This situation can be changed, if microalgae are used for theproduction of biodiesel. A very less cropping area would be required for algalbiomass production that satisfies approximately 50% need of the transport fuelof any country. Table 2 shows the comparison of biodiesel on the basis of croptype.                  Table 1 Oil content of microalgae Microalga                            Oil content (% dry weight)Cylindrothecasp.                 16-37Monallanthussalina             20Dunaliellaprimolecta           23Chlorellasp.                        28-32Nannochlorissp.

                  20-35Nitzschiasp.                                    45-47Schizochytriumsp.                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                             45Coconut                  2689                             99Jatropha                  1892                             140Canola                    1190                             223Soybean                  446                               594Corn                       172                               1540Microalgae (30 % oil dry wt. basis)                                                                                        136900                          2Microalgae (70% oil dry wt.basis)                                                                                         58700                           4.5(Source: Chisti, 2007) In view of this, microalgal biomass would be the only sourcefor biodiesel which have the potential to completely replace the fossil fuel.Microalgae are capable of production all the year, therefore oil productionfrom microalgae exceeds from the other oil-seed crops.

For example: Biodieselyield 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 thanother 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. Microalgaehave fast growth rate and double their biomass within 24 h and sometimes duringexponential growth as short as 3.5 h. Many of the species have oil content inthe range of 30-80% dry weight of biomass and can exceed 80% by weight of drybiomass (Spolaore et al. 2006). Also microalgae help in fixing CO2from the atmosphere and thereby reducing the green-house gases. Nutrients usedfor microalgae cultivation can be obtained from the waste water released fromagro-food industries and thereby helps in waste water treatment.

Algal biomasscan also be used as feed or as a fertilizer for crops and along with this it canalso produce co-products such as proteins (Guschina and Harwood, 2006).Microalgae doesn’t not require any pesticide or herbicide application (Rodolfiet al. 2008). It has the potential to increase the oil yield significantly byvarying the growth conditions.

Microalgae capable of producing bio-hydrogenphoto-biologically (Ghirardi et al. 2000).These above combination of biodiesel production, fixation ofCO2, biological treatment of waste water, bio-hydrogen production, ethanol andmethane production underscore the potential of microalgae. Despite thesepotentials of microalgae, many challenges have slowed the development of algalbiofuel technology to commercial form. There should not be a single strain tillnow developed which is capable of producing biodiesel in great quantities(Brennan and Owende, 2009). Lacking of techniques for CO2 diffusionlosses and attaining higher photosynthetic efficiencies (Ugwu et al.

2008).There are very few commercial plants in production area, therefore lack of datafor large scale plants (Pulz et al. 2001).


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