A flocculation strategy for harvesting high lipid content microalgae biomass

The recovery of biomass using flocculation is a procedure economically viable, however, it may cause damage to the cells and loss of the metabolic product of interest, such as lipids, according to the flocculant used and its concentration. In this work, different flocculants were evaluated for the flocculation of microalgae biomass of Acutodesmus obliquus, aiming to achieve a biomass recovery efficiency similar to that of a centrifugation process, with minimum loss of lipid content. Flocculation was tested with ferric chloride (FeCl₃) and sodium hydroxide (NaOH) at different concentrations and compared to a sample centrifuged at 7000 rpm. The evaluated parameters were remaining absorbance (540 nm) in the clarified medium, and concentration of lipids in the recovered biomass. When FeCl₃ was used at 0.2 mmol·L^-1 as flocculant, the biomass recovery efficiency was as high as 96.8%. Meanwhile, the highest efficiency with NaOH, 93.5%, was achieved at 8 mmol·L^-1. The efficiency with centrifugation was lower than with either flocculants: 91.7%. However, flocculation with NaOH caused a significant reduction in lipid content, which did not occur with FeCl₃. Flocculation efficiency is also shown to be influenced by initial salt concentration in the culture medium, with a reduction of 79% in efficiency when nutrients concentration increases to 9 mL·L^-1 of cultivation.