Evaluation of natural flocculant efficiency in the harvest of microalgae Monoraphidium contortum

This study assesses two parameters that can result in high efficiency in the recovery of the microalgae Monoraphidium contortum. The significant contribution of this paper is to test different coagulants in different conditions of concentration in the coagulation and flocculation processes followed by sedimentation to evidence the best coagulant and the best condition for harvesting of Monoraphidium contortum biomass. So the proposed methodology aimed to perform preliminary tests using a tannin-based cationic coagulant (TANFLOC SG®), FeCl2, and Al2 (SO4)3, where they were performed at concentrations of 0, 20, 40, 60, 80, and 100 mg L−1 at a fast mixing speed of 400 RPM. The tests determined 20 mg L−1 of Tanfloc SG® as the most efficient turbidity reduction in the preliminary test. The obtained results were used to construct a non-factorial central composite planning. Therefore, after a design of experiments, the study outcome shows the best turbidity removal range from the main tests came at 35 mg L−1 and 550 RPM of fast mixing speed.

THE HARVESTING OF HIGH LIPID CONTENT MICROALGAE BIOMASS THROUGH A FLOCCULATION STRATEGY

Different flocculants were evaluated for the flocculation of microalgae biomass of Acutodesmus obliquus. Flocculation was tested with FeCl3 and NaOH at different concentrations and compared to a sample centrifuged at 7000 rpm. The evaluated parameters were absorbance (540 nm) in the clarified medium, and lipids concentration. For FeCl3 (0.2 mmol L-1) as flocculant, efficiency was 96.8%, and with NaOH (8 mmol L-1) 93.5%. Centrifugation efficiency was lower than with either flocculants: 91.7%. However, NaOH flocculation reduced lipid content, which did not occur with FeCl3. Flocculation efficiency was affected by salt concentration, reducing efficiency by 79% due to increased nutrient concentration (9 mL L-1).