Biomass and Lipid Content in Potential Green Algal Species for Biodiesel Production

The ever increasing world population and anthropogenic energy requirements, has necessitated the need for the scientific community to look out for novel/alternate sources of energy. Alternate fuels especially biodiesel is now known as a promising option to support our ever growing energy needs. Biodiesel was earlier produced from plant oil seeds such as Jatropha, Pongamia, Madhuca, Sunflower, etc., however, microalgae are presently studied widely as the next generation source of biofuels. Microalgae are miniature plants which photosynthesize and utilize atmospheric carbon dioxide and sunlight for their growth and multiplication. Microalgae produce lipids in substantial amounts which may be extracted and used for biodiesel production. Microalgae may be grown mixotrophically/ heterotrophically i.e., under the effect of carbon sources to accumulate higher amount of lipids. Certain wastes contain valuable carbohydrates which could act as a good carbon-rich source for the growth of algae especially enhancing lipid contents in the same. The wastes after recovery of carbohydrates may be disposed of either in incinerators or landfills.

Different types of waste carbon sources have been used to enhance biomass growth and lipid accumulation in microalgae. Some readily available chemical compounds such as glucose, acetate and glycerol have shown to expedite growth and lipid accumulation inChlorella protothecoides  and Phaeodactylum tricornutum. Liu et al. used various carbon sources to study Chlorella zofingiensis as a feedstock for biodiesel production and found glucose as one of the best source. Heterotrophic growth of algae also led to 900% increase in lipid production in case of Chlorella zofingiensis with glucose as organic carbon source. Corn starch hydrolysate has been used for enhancement of lipid content by 20% in C. protothecoides. Molasses has also been used for the enhancement of biomass productivity in a prokaryotic alga, Spirulina platensis. Press mud extract and cane molasses were used to enhance the lipid content in C. minutissima. Liang et al. studied the effect of glycerol and glucose on the growth and lipid content of C. vulgaris which resulted in high increases in biomass production. B. braunii also showed enhancement in the lipid content with different sugars such as glucose, mannose, fructose. Various inexpensive and low cost carbon feed stocks from waste have also been used for algal growth which has been extensively reviewed by Subramanian et al. Some other nutrient sources such as sodiumthiosulphate , swine waste water and iron have been used for the enhancement of growth and lipid content in various green algal species such as Scenedesmus and Chlorella. Sugars have also been converted to oil in C. vulgaris by using a photosynthetic fermentation model which resulted in improvement of growth and lipid content . Further, Taylor et al.used the ethyl acetate extract of two algal species Skeletonema marinoi and Dunaliella salina for enhancement of growth of Nannochloropsis oculata.