Bioflocculation of microalgal biomass and bioethanol production using wastewater-derived Cyberlindnera jadinii

Bioflocculation is a promising and cost-effective strategy for microalgae harvesting within sustainable biorefinery and circular economy frameworks. However, the liquid fraction generated after biomass recovery is often underutilized, despite its potential as a substrate for value-added product generation. This study evaluated an indigenous wastewater-derived yeast, identified as Cyberlindnera jadinii, as a bioflocculant for microalgae biomass harvesting and assesses the subsequent valorization of the recovered supernatant for bioethanol production. The bioflocculation process was evaluated using a Box–Behnken experimental design combined with response surface methodology to investigate the effects of standardized yeast suspension volume, glucose concentration, and agitation speed on biomass recovery. Biomass recovery efficiencies above 80% were achieved after 30 min of settling under the optimal combination of standardized yeast suspension volume, glucose concentration, and agitation speed evaluated by the Box–Behnken design. The recovered supernatant supported bioethanol production above 10 g L−1 after glucose supplementation. These results indicate the feasibility of integrating yeast-assisted bioflocculation and downstream ethanol production in wastewater-based microalgae systems. However, further work is required to validate the process at pilot scale, clarify the mechanism involved in yeast-microalgae aggregation, and establish complete carbon mass balances.