Value-added Lipids Extraction From Wet Microalgae Using Ionic Liquids
Abstract
Microalgae have gained interest as sources of renewable lipids in the biofuel sector due to their ability to sequester carbon dioxide into triacylglycerol (TAG), a biodiesel feedstock. However, industrial-scale production of microalgae exclusively for fuel production is limited by technical and economic challenges. Some marine microalgae can accumulate large amounts of polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and other unsaturated fatty acids, which are high-value compounds linked to the prevention of various cardiovascular diseases. This thesis therefore examines the extraction of lipids and DHA from two microorganisms (Chlorella vulgaris, a model organism for lipid production, and Thraustochytrium sp., an industrially relevant DHA producer).
Ionic liquids (ILs) have been shown to assist in cell disruption and lipid extraction from microalgae. A recently described ionic liquids were therefore synthesized and characterized for lipid extraction. It was used in comparison with commercially available ILs throughout this thesis. Initially, lipid extraction was evaluated from dry samples of the model organism C. vulgaris, followed by the processing of wet extraction from fresh algae samples. Treating wet biomass is technically more challenging, but a necessity, as complete dewatering and drying in economically not feasible. To further enhance the IL-mediated extraction and cell disruption the previously evaluated process was combined with electrolysis. Electrolytic pre-treatment of microalgae can disrupt the cell wall, aiding in the release of intracellular lipids. ILs have high electric conductivity and hence synergies were expected when combining these two treatments. The obtained extraction efficiency was up to 44.53 ± 2.38% for the combined process compared to 29 ± xx % with ILs only and 1.52 ± 0.74% with electrolysis only.
Extraction technologies developed with C. vulgaris were subsequently transferred to extract value-added lipids fromThraustochytrium sp. (T18) which possesses a high polyunsaturated fatty acids (PUFAs) content, with a specifically large percentage of omega-3 fatty acids such as docosahexaenoic acid (DHA). Two ILs were assessed for their ability to facilitate the extraction of PUFAs from dry and fresh Thraustochytrium sp. (T18) cultures. The results show that ILs could facilitate the extraction of over 90% (w/w) of the available oils from dried T18 biomass and still maintain an extraction efficiency of around 80% (w/w) when using wet slurry.
Subsequently, the extra18 using the synthesized IL was optimized using a central composite design (CCD) and response surface methodology (RSM). The total extraction efficiency was up to around 97% of DHA-rich oil, showing that ionic liquid based methods might be suitable to process marine micro-algae with value-added lipid composition.