Efficient Harvesting of Nannochloropsis Microalgae via Optimized Chitosan‐Mediated Flocculation

Food‐grade rather than synthetic or chemical flocculants are needed for microalgae harvesting by settling, if used for food products. Chitosan is effective in harvesting freshwater microalgae, but it is expensive and typically not suitable for marine microalgae like Nannochloropsis. To minimize costs for food‐grade flocculation, a number of potentially important parameters are considered, including chitosan solubility and optimized chitosan‐mediated flocculation of Nannochloropsis sp. BR2 by a five‐factor central composite design experiment. Results show that an optical density (440 nm) of 2 (0.23 g dry weight L−1), initial pH of 6, final pH of 10, and 22 ppm chitosan with a viscosity of 1808 cP provide optimum flocculation efficiency, which is predicted to be in the range of 97.01% to 99.93%. These predictions are verified on 4.5 and 8 L Nannochloropsis sp. BR2 cultures. Microalgae can be grown for food, feed, or fuel without competing for arable land or freshwater. However, food‐grade flocculants are needed for microalgae harvesting by settling, if used for food products. This work demonstrates that small quantities of chitosan are sufficient for the harvesting of the difficult‐to‐harvest marine microalga Nannochloropsis sp., which is high in omega‐3 fatty acids.