• Energy Research
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Abstract Excessive use of fossil fuels to satisfy our rapidly increasing energy demand has created severe environmental problems, such as air pollution, acid rain and global warming. Biofuels are a potential alternative to fossil fuels. First- and second-generation biofuels face criticism due to food security and biodiversity issues. Third-generation biofuels, based on microalgae, seem to be a plausible solution to the current energy crisis, as their oil-producing capability is many times higher than that of various oil crops. Microalgae are the fastest-growing plants and can serve as a sustainable energy source for the production of biodiesel and several other biofuels by conversion of sunlight into chemical energy. Biofuels produced from microalgae are renewable, non-toxic, biodegradable and environment friendly. Microalgae can be grown in open pond systems or closed photobioreactors. Microalgal biofuels are a potential means to keep the development of human activities in synchronization with the environment. The integration of wastewater treatment with biofuel production using microalgae has made microalgal biofuels more attractive and cost effective. A biorefinery approach can also be used to improve the economics of biofuel production, in which all components of microalgal biomass (i.e., proteins, lipids and carbohydrates) are used to produce useful products. The integration of various processes for maximum economic and environmental benefits minimizes the amount of waste produced and the pollution level. This paper presents an overview of various aspects associated with biofuel production from microalgae, including the selection and isolation of microalgal species, various cultivation and harvesting techniques as well as methods for their subsequent conversion into biofuels.

The present study has been designed to optimise certain important process parameters for Scenedesmus vacuolatus to achieve efficient carbon dioxide extenuation as well as suitable fatty acid profile in context to improve biodiesel properties. The effect of varying sodium bicarbonate concentration was evaluated in single and multicomponent system such as nitrate, phosphate, inoculum size to observe interactive effects on algae biomass production, carbon dioxide (CO2) removal efficiency and fatty acid methyl ester (FAME) profile. Maximum biomass productivity of 117.0 ± 7.7 mg/L/day with 3 g/L of sodium bicarbonate was obtained i.e. approximately 2 folds higher than the control. Under multicomponent exposure, maximum biomass of 1701.5 ± 88.8 mg/L and maximum chlorophyll concentration of 15.3 ± 6.4 mg/L were achieved on 14th day at 3 g/L sodium nitrate, 0.1 g/L dipotassium hydrogen phosphate, 2 g/L of sodium bicarbonate and initial cell density of 0.3 (N3P0.1B2OD0.3). FAME content of 46.1 mg/g of biomass was obtained at this combination which is approximately 3 folds higher than the FAME content obtained under nitrogen and phosphate deprivation (16.6 mg/g at N0P0B2OD0.3). Confocal microscopy images confirmed the results with enhanced lipid droplet accumulation at high bicarbonate concentration as compared with the control. This interactive study concluded the variability in FAME profile along with the exposure to varying nutrient concentrations.

Abstract The main aim of the present study is to understand algae behaviour and enhancement of the intracellular neutral lipid content of freshwater green microalgae, Scenedesmus vacuolatus, under salt exposure. Effects of various salts (sodium chloride, magnesium chloride and calcium chloride) on this species were analysed by measuring parameters such as growth rate, chlorophyll content, neutral lipid intensity and conducting FAME profiling. When under stress, microalgae divert their metabolic pathways towards lipid synthesis, and this is evidenced in the current study. Compared to controlled and unmodified media cultivation, sodium chloride and magnesium chloride exposure promoted 383% and 340% higher fluorescence intensities, respectively, and there was a significant increase in the FAME content, particularly of saturated fatty acids (such as palmitic and stearic acid) at a magnesium chloride concentration of 50 mM and calcium chloride exposure of 70 mM, with percentage increases of 109% and 253%, respectively, compared to the control. Algal cells were found to be more tolerant towards NaCl than other salts, and this was confirmed through the biomass accumulation profile. Biomass productivity was highest at exposure to 100 mM sodium chloride (33 mgL−1d−1) followed by calcium chloride (19.5 mgL−1d−1) and magnesium chloride (12.6 mgL−1d−1). Confocal imaging further supported the results, and scanning electron microscopy revealed changes in algal surface morphology. This study provides further information about stress-driven lipid biosynthesis and analyses changes in cellular morphology and physiology. However, further exploration and systematically studies are required to determine exact mechanism involved in neutral lipid enhancement inside cells and associated metabolomics.