Bioflocculation of cyanobacteria with pellets of Aspergillus niger: Effects of carbon supplementation, pellet diameter, and other factors in biomass densification.

One of the hurdles of renewable energy production from photosynthetic microorganisms is separating the biomass from water in cultures. Bioflocculation with filamentous fungus Aspergillus niger, an alternative low-cost method used for such separation, was studied with four cyanobacteria. Cocultures with Spirulina maxima and Synechococcus subsalsus resulted in bioflocculation efficiencies up to 94%, while with Anabaena variabilis and Anabaena siamensis bioflocculation did not occur. S. subsalsus was selected to evaluate the effect of cyanobacterial initial concentration, fungal:cyanobacterial ratio, carbon supplementation, and pH on biomass densification. Bioflocculation efficiencies up to 98% in 48 h were obtained with fungal:cyanobacterial ratio 1:5 and carbon supplementation. Despite the lower efficiency (54%), the highest concentration factor of S. subsalsus suspension (62.8 - from 0.9 to 56.5 g/L) was obtained with ratio 1:5 without supplementation. This result was attributed to the smaller pellet diameter (2.5 mm) and indicated that lower pellet growth is better for biomass densification.