Microalgal cell disruption by hydrodynamic cavitation for the production of biofuels

Cell disruption is an essential pre-treatment for the efficient extraction of many types of intracellular metabolites such as proteins, carbohydrates, DNAs or lipids; but the high process energy requirement becomes an important issue for low valued commodities such as biofuels. Current mechanical cell disruption methods such as high-pressure homogeniser or sonication require energy input in the order of hundreds of MJ kg of the dry mass; in addition, these methods do not have the capacity suitable for biofuel production where daily processing volumes are in order of mega litres. This study investigated hydrodynamic cavitation (HC) as a cell disruption technique, with levels of disruption determined by i) lipids extracted and ii) the chlorophyll released. It was found that for the lipid extraction, HC has a disruption energy requirement of 3 MJ kg. This amount of energy requirement is more efficient than sonication by a factor of 10; however, it still represents nearly 13 % of the total energy in the biomass and is too high for the production of biofuels. The cell disruption by HC is essentially periplasmic, i.e. mainly confined to the cell wall and membrane. This result suggests that damage to the outer cell barrier such as the cell wall was sufficient to allow for the diffusion of solvents for lipid extraction.