Browsing by Subject "Lipid"

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    Aeration energy requirements for lipid production by Scenedesmus sp. in airlift bioreactors
    (Elsevier, 2014) Jones, S M J; Harrison, S T L  
    Microalgae have potential to yield various bioenergy products, including algal biodiesel. For algal energy production, the process energy input must be substantially lower than the product energy. Airlift photobioreactors provide controlled environments with good mixing and mass transfer; however, previous work reports a net energy ratio (NER; energy produced divided by energy consumed) less than 1. Here, the energy consumption in these reactors was improved by combined optimisation of superficial gas velocity and its CO2 concentration. Increasing CO2 concentration resulted in increased tolerance to lower superficial gas velocities, down to a critical minimum value. A 75% reduction in aeration power input was obtained by reducing superficial gas velocity from 0.0210 to 0.0052 m s− 1 at 5 400 ppm CO2, without substantial reduction in biomass concentration (2.27 to 1.93 g L− 1, respectively) or productivity (0.189 to 0.173 g L− 1 d− 1, respectively). The NER under these conditions was 5.47 for biomass plus lipid and 1.01 for lipid only. The CO2 supply rate, product of superficial gas velocity and CO2 concentration, correlated with the CO2 transfer rate which influenced algal productivity. The range of NERs measured across the superficial gas velocities studied indicates the ability to optimise algal cultivation in photobioreactors for the improved feasibility of algal bioenergy.
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    Selection of direct transesterification as the preferred method for assay of fatty acid content of microalgae
    (Springer Verlag, 2010) Griffiths, M J; van Hille, R P; Harrison, S T L
    Assays for total lipid content in microalgae are usually based on the Folch or the Bligh and Dyer methods of solvent extraction followed by quantification either gravimetrically or by chromatography. Direct transesteri- fication (DT) is a method of converting saponifiable lipids in situ directly to fatty acid methyl esters which can be quantified by gas chromatography (GC). This eliminates the extraction step and results in a rapid, one-step procedure applicable to small samples. This study compared the effectiveness of DT in quantifying the total fatty acid content in three species of microalgae to extraction using the Folch, the Bligh and Dyer and the Smedes and Askland methods, followed by transesterification and GC. The use of two catalysts in sequence, as well as the effect of reaction water content on the efficiency of DT were investigated. The Folch method was the most effective of the extraction methods tested, but comparison with DT illustrated that all extraction methods were incomplete. Higher levels of fatty acid in the cells were obtained with DT in comparison with the extraction-transesterification methods. A combination of acidic and basic transesterifi- cation catalysts was more effective than each individually when the sample contained water. The two-catalyst reaction was insensitive to water up to 10% of total reaction volume. DT proved a convenient and more accurate method than the extraction techniques for quantifying total fatty acid content in microalgae.