An effective method for harvesting of microalga: Coculture-induced self-flocculation

Abstract Microalgae are potential candidates for the production of third-generation biofuels, but the high-energy consumption of harvesting biomass makes current commercial microalgal biodiesel production economically unfeasible. Self-flocculation is regarded as a cost-efficient strategy for harvesting microalgae. In this work, a coculture system was developed by the mixotrophic cultivation of two poorly flocculating microalgae, Desmodesmus sp. ZFY and Monoraphidium sp. QLY-1, for self-flocculation of microalgal cells. The flocculation efficiency for harvesting was enhanced to 85.33% with settling for 4 h in coculture, which was better than that in mono-culture (57.98% and 32.45%). Coculture resulted in changes in both the concentration and composition of extracellular polymeric substances (EPS) in the culture, which partially contributed to cell aggregation. The concentration of polysaccharides in LB-EPS ranged from 27.01% and 27.35% in mono-culture to 46.53% in coculture. Moreover, the fine properties of lipid productivity (93.99 mg L −1  d −1 ) and fatty acid composition in coculture indicated the potential to produce biodiesel within most biodiesel standards.