Disruption of microalgal cells for the extraction of lipids for biofuels: Processes and specific energy requirements

Some species of microalgae have high lipid yields; however, all species of microalgae, with the only known exception of Botryococcus braunii, have their lipids located inside the cells. The toughness of cell walls and cell membranes of microalgae makes the lipids not readily available for extraction and means that cell disruption an energy intensive process. The cell disruption energy required may become a critical consideration in the production of low valued commodities such as biofuels. This study provides an overview of microalgal cell disruption processes which are potentially suitable for large scale lipid extractions. The energy requirements of these processes were calculated and then compared with estimates of the theoretical minimum energy required for disruption. The results show that the mechanical disruption methods considered were highly energy inefficient when conducted under laboratory conditions and required a specific energy consumption of at least 33 MJ kg −1 of dry biomass. Thus the specific energy consumption is greater than the energy recoverable from the microalgae and is also a factor of 10 5 greater than that the estimated minimum theoretical energy consumption. This result clearly shows that further research and innovation is required for the sustainable cell disruption and lipid extraction from microalgae.