Microalgal bio-refinery approach for utilization of Tetradesmus obliquus biomass for biodiesel production

Abstract

The speedy depletion of fossil fuels demands a more sustainable and renewable source for biofuel production. In this view, one promising alternative to petroleum diesel is microalgal-biodiesel, as it can grow on non-arable land, consumes CO2 for growth and most of them can withstand extreme temperature variations. Simultaneously, microalgae are promising producers of various other biofuels, such as bioethanol, glycerol and biomaterials like pigments and carotenoids. The present study emphasizes on microalgal bio-refinery of an isolated microalgae Tetradesmus obliquus SGM19; producing biodiesel, bioethanol and glycerol. The strain exhibited high lipid (28 ± 1.2%), carbohydrate (24 ± 0.8%) and protein (42 ± 0.67%) concentrations, which makes it a promising feedstock for biofuels. The isolate was also found rich in pigments such as chlorophyll and carotenoids (with high antioxidant activity), which allows their utilization like food and pharmaceutical supplements. The biomass of T. obliquus SGM19 was subjected to lipid extraction followed by bioethanol synthesis (from the carbohydrates present in leftover biomass). The extracted lipid was transesterified to produce fatty acid methyl esters (FAME), which was characterized with GC–MS. The transesterification process was a 2-step acid-based catalyzed reaction and was optimized for reaction time, reaction temperature and oil to solvent ratio. At optimum conditions, the major components of FAME obtained from T. obliquus SGM19 were palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0), oleic (C18:1) and linoleic (C18:2) acids, making it suitable to be used as biodiesel. The properties of the biodiesel produced were well within the range of the ASTM standards.