Immobilization of microalgae on exogenous fungal mycelium: A promising separation method to harvest both marine and freshwater microalgae

•Biological harvesting of microalgae via immobilization on fungal mycelium.•Screening fungi to immobilize microalgae.•Optimization of microalgae (Nannochloropsis sp.) immobilization on fungal mycelium.•Maximum 97% microalgae cells were immobilized and naturally precipitated.•Separation of immobilized microalgae using sieve and reuse of de-algated culture medium. Although various methods have been developed for microalgae harvesting, problems such as chemical toxicity, low efficacy, low flexibility, and high cost, still remain with the current methods. In the present study, an effective biological separation method has been developed to harvest microalgae via immobilization on exogenous fungal mycelium. Fungal mycelium was added into microalgae culture and air mixed for the immobilization. The immobilized microalgae with fungal mycelium were naturally precipitated within 10min after stopping the mixing. Both marine (e.g. Nannochloropsis sp.) and freshwater (e.g. Chlorella vulguris) microalgae were almost completely (94–97%) precipitated using the mycelium of Aspergillus nomius CCK-PDA 7#6. The precipitated mixed biomass was separated by simple filtration using sieve. A 70% initial nutrients supplement to de-algated culture medium gave high growth yield (0.43g/l) in subsequent microalgae cultivation. The mycelium can be obtained free or at low-cost as waste from a fungal fermentation process of producing valuable products. The developed method is, therefore, very promising for economical harvesting of microalgae.