Characterization of fatty acids and hydrocarbons of chlorophycean microalgae towards their use as biofuel source

Microalgae accumulate important biofuel precursors such as fatty acids and hydrocarbons. Identification of microalgal strains with ideal fuel quality precursor profile is important during bioprospection studies. In this direction, thirty two freshwater green microalgae were characterized for their biomass productivity, fatty acid and hydrocarbon composition under autotrophic growth conditions. Scenedesmus dimorphus CFR 1-05/FW, Oocystis pusilla CFR 6-01/FW and Quadrigula lacustris CFR 7-01/FW were high biomass producing strains with shorter doubling time. Lipid accumulation was monitored by nile red staining with mild acetic acid pretreatment (at 7 m mol L−1) to microalgal cells. Six strains viz., S. dimorphus CFR 1-05/FW, Scenedesmus obtusus CFR 1-09/FW, Chlorococum sp. CFR 2-01/FW, C. humicola CFR 2-03/FW, Chlorella sorokiniana CFR 3-01/FW, Dictyosphaerium CFR 5-01/FW showed lipid accumulation of >20% mass fraction at stationary phase. Palmitic, oleic and alpha linolenic acids were major fatty acids in all the chlorophycean species. Fuel grade hydrocarbons which can be directly blended with petroleum fuels were identified. Fourteen strains showed hydrocarbon content of >10% mass fraction of dry biomass. n-Paraffins of chain length between C15 to C20 were predominant hydrocarbons in all the strains. Branched isoprenoid hydrocarbons were detected in Scenedesmus sp. CFR 1- 13/FW constituting 49% mass fraction of total hydrocarbons. High quantities of n-tetradecane (40%) was detected in Kirchneriella cornuta CFR 8-01/FW. The similarity of microalgal hydrocarbon profiles with paraffinic and isoparaffinic fraction of petroleum diesel and compliance of FAME based biodiesel to international standards indicate the suitability of algae derived biofuels for blending with conventional petroleum fuels.