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.

Microalgae cultivation offers a sustainable approach for nutrient recovery from municipal effluents and the production of valuable biomass, although efficient harvesting remains challenging. This study evaluated the adaptation of the microalgal consortium MC-10 in a sequential batch system through reinoculation of its flocculating fraction to enhance harvesting efficiency and mineral recovery. The consortium was initially cultivated under high ionic stress to promote cell aggregation. Laboratory preadaptation using secondary municipal effluents was then conducted, followed by an outdoor evaluation. In the initial propagation stage, flocculation efficiency reached 98%. Using municipal effluents, flocculation values of 99% were obtained, with a 149% increase in flocculating biomass under laboratory conditions, and 84% flocculation with a 125% increase in biomass production under outdoor conditions, demonstrating the consortium’s stability under environmental fluctuations and its suitability for biomass harvesting. The resulting biomass showed high potential as a biofertilizer due to its mineral content (47% dry weight, DW) and acid solubility (83%), indicating high nutrient bioavailability. Additionally, it contained a total carotenoid concentration of 451 μg/g DW, adding antioxidant value. These findings support the use of microalgae cultivation for the valorization of municipal effluents through the production of easily harvestable biomass with potential for reintegration into agricultural systems.