Abstract
Microalgal lipid recovery for biodiesel production is currently considered suboptimal, but pre-treatment of algal biomass, the use of solvent mixtures and the positioning of transesterification can lead to increased yields. Here, the effect of various reportedly successful pre-treatments and solvent mixtures were directly compared to each other and combined with direct and indirect transesterification methods using the oleaginous microalga Tetraselmis sp. M8. Microwave and thermal pre-treatments were applied and the total lipid and fatty acid methyl ester (FAME) recoveries were investigated. The application of pre-treatments increased FAME recovery through indirect transesterification when a Soxhlet system was used but they had no significant effect for direct transesterification. Gravimetric analyses of total lipids revealed that lipid recovery was highest when utilizing the chloroform-based Bligh and Dyer extraction method; however FAME yield was the highest when applying a Soxhlet system utilizing a solvent mixture of hexane-ethanol (3:1). Total lipid recovery did not necessarily correlate with the recovery of FAMEs. The highest FAME recovery was achieved from thermal or microwave pre-treated biomass followed by indirect transesterification through Soxhlet extraction. FAME recovery could be more than doubled (increase of up to 171%) under these conditions. We conclude that a simple thermal pre-treatment (80°C for 10 min) in combination with solvent mixture extraction through indirect transesterification may present a cost-effective and scalable option for large-scale lipid extraction from microalgae.
Highlights
Oils from microalgae are an attractive and promising resource for biodiesel production (Amin, 2009; Johnson and Wen, 2009; Demirbas and Fatih Demirbas, 2011) but challenges remain in microalgae harvesting and lipid extraction technologies (Yoo et al, 2012)
Fatty acid methyl esters (FAMEs), which are the basis of biodiesel, can be produced by transesterification of algal oil [triacylglycerides (TAGs)] with methanol using either acids or bases as catalysts and resulting in the formation of glycerol as a byproduct (Canakci and Van Gerpen, 1999; Knothe, 2005; Chisti, 2007; Demirbas, 2008)
The lipids must first be extracted from the microalgal cells, and as the cell walls are generally thick or lipids are associated with organelles or other cellular structures, lipid extraction remains a major bottleneck for algae-derived biodiesel production (Mercer and Armenta, 2011; Yoo et al, 2012)
Summary
Oils from microalgae are an attractive and promising resource for biodiesel production (Amin, 2009; Johnson and Wen, 2009; Demirbas and Fatih Demirbas, 2011) but challenges remain in microalgae harvesting and lipid extraction technologies (Yoo et al, 2012). The approaches for cell disruption that have been widely trialed to date range from mechanical methods (such as milling) to chemical (acid/base for cell lysis) and physical (such as sonication, microwave, and thermal) techniques (Kita et al, 2010; Mercer and Armenta, 2011). These pre-treatments have been shown to break, or at least weaken, the cell wall and internal structures, which facilitated more efficient oil extraction. Direct transesterification, which has been considered as a candidate for large-scale biodiesel production, has been reported to be at least 15–20% more efficient over extraction-transesterification experiments (indirect transesterification) (Lewis et al, 2000; Levine et al, 2010)
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