Microalgae, like higher plants, produce storage Lipids in the form of triacyglycerols (TAGs). Comparatively algae produce more oil than any other oilseeds which are currently in use. Many microalgal species can be induced to accumulate substantial quantities of lipids, often greater than 60% of their biomass.
Comparison of average oil yields from algae with that from other oilseeds
The table below presents indicative oil yields from various oilseeds and algae. Please note that there are significant variations in yields even within an individual oilseed depending on where it is grown, the specific variety/grade of the plant etc. Similarly, for algae there are significant variations between oil yields from different strains of algae. The data presented below are indicative in nature, primarily to highlight the order-of-magnitude differences present in the oil yields from algae when compared with other oilseeds. (See also: Vegetable Oils Yields & Characteristics – from Journey to Forever)
Yields ( Gallons of oil per acre per year )
Oil content of few microalgal species:
|Microalgal species||Oil content(% dw)|
|Chlorella protothecoides(autotrophic/ heterothrophic)||15-55|
|Cyclotella DI- 35||42|
The key question in everyone’s mind is: which is the best species of algae for biodiesel? The decades-long research undertaken by NREL of USA – called the Aquatic Species Program (see a copy of the Aquatic Species Program Research notes here, but please remembers it is a large PDF file!) suggested few high-oil-containing algae strains.
The strains of Algae most favoured by the NREL researchers were Chlorophyceae (green algae). Green algae tend to produce starch, rather than lipids. Green algae have very high growth rates at 30oC. The other algae favoured by NREL researchers are diatoms. However, the Diatoms need silicon in the water to grow, whereas green algae require nitrogen to grow.
The lipid and fatty acid contents of Microalgae vary in accordance with culture conditions. Microalgae are known to accumulate more lipids in nutrient deficient conditions. Researchers identified the most dramatic increases in the lipid content of the cultures during N-deficient conditions. Biochemical studies have also suggested that acetyl-CoA carboxylase (ACCase), a biotin-containing enzyme that catalyzes an early step in fatty acid biosynthesis, may be involved in the control of this lipid accumulation process. Therefore, it may be possible to enhance lipid production rates by increasing the activity of this enzyme via genetic engineering.
Theoretical maximum yields of few microalgae in open ponds:
|Species||Yield (in g/m2/day)|
|Marine Nannochloropsis||20 (~ 30% lipids)|
Research experiments are however carried out to determine exactly how promising algae biofuel production can be by tweaking the inputs of carbon dioxide and organic matter to increase algae oil yields.
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