Biomass recovery and lipid extraction processes for microalgae biofuels production: A review

Cell genetics, culture conditions and the recovery efficiency of cells and products are the bottlenecks for industrial bioprocesses from microalgae. Microalgae lipids can be used for different applications, e.g., drugs, food, and biofuels, and their purpose considers the nature and concentration of the lipids that are wished to obtain. For the biotechnological production of lipids, adequate culture conditions are necessary to enable the cell strain to obtain high biomass and lipid yields and productivities. Also, the processes of separating the cells from the culture medium and releasing the lipids from that biomass need to be efficient and economically viable. Considering that cultivation, cell recovery and lipid extraction directly reflect the results obtained, the most appropriate methods for these operations must be applied. Many literature reviews report the lipid and fatty acid contents obtained through the cultivation of different microalgae species and strains. However, few studies relate the contents of these biomolecules, either with the methods of obtaining the biomass or with the extraction of lipids. Even so far there is no review in the literature with such an approach. The aim of this work was to review and discuss the culture conditions for different microalgae strains and their influence on lipid content; the separation of microalgae biomass, including biomass thickening methods, and methods of biomass depletion; the methods of cellular disruption and lipid extraction; the influence on biofuels' production, e.g. biodiesel, bioalcohols and biohydrogen; and the influence of green chemistry (solvents and extraction technologies) for a sustainable production of biofuels under the concept of biorefinery.