Flocculation mechanism of Aspergillus niger on harvesting of Chlorella vulgaris biomass

Fungal flocculation and its mechanism are rarely observed on biofuel-producing microalgae. In this study, the flocculation activity and mechanism of Aspergillus niger hsn26, a filamentous fungus, on Chlorella vulgaris biomass was investigated for the first time. Mycelial pellets showed high flocculation efficiency on algal cells. Moreover, the source of flocculation activity is located at the surface of mycelium. The characteristics of flocculation activity indicated that surface proteins with low molecular weight play a significant role during flocculation process. Calcium can be added into algal culture as coagulants to significantly improve flocculation efficiency. Calcium addition can also simultaneously bind the surfaces of mycelium and algal cells. Therefore, calcium bridging is the main flocculation mechanism for mycelial pellets. The increase of hydrophobic interaction can also promote the flocculation activity. Lastly, results indicate that flocculation mechanism of mycelial pellets on microalgae biomass is a surface proteins-mediated, calcium bridging-dependent and hydrophobic interaction-involved process.