Some implications of natural increase of pH in microalgae cultivation and harvest by autoflocculation

Abstract

Microalgae hold great potential for producing purified high-value products (e.g. pigments and polyunsaturated fatty acids) and represent a source of bioavailable nutrients in aquaculture feeds; however, its production is limited by the high costs of harvesting. Recently, microalgae autoflocculation has been considered a useful solution due to the easy recovery of cell aggregates and natural increase in pH that prevents cell lysis. This work evaluates some cultivation conditions that could contribute to autoflocculation, such as natural pH increase and precipitate formation over the productivity and flocculation of 16 microalgae consortia. Results showed a biomass production of 1.4 to 4.4 dry weight (g L-1) and high flocculation of 81 to ~100%, probably due to Ca3(PO4)2 formation. Moreover, the alkaline pH could have facilitated the assimilation of CO2 and explained the increase of inorganic carbon in the solution obtained. Likewise, results showed a marked descent in electrical conductivity (EC) in solution and high mineral content in the biomass (21.4-35.9%). Finally, this study suggests that the studied culture conditions facilitated microalgae harvest, and the resulting biomass could be a source of bioavailable dietary minerals. Therefore, some of these results might be addressed in future studies with individual microalgae species.