Bio-harvesting and pyrolysis of the microalgae Botryococcus braunii

• 500 l-scale cultivation of B. braunii strains Kossou-4 and Overjuyo-3.
• Screening of fungal isolates led to selection of bioflocculation candidate.
• Aspergillus fumigatus successfully used to harvest up to 98% of biomass.
• Ultimate and pyrolysis analyses showed no impairment of feedstock value by fungus.
• First time A. fumigatus used for economical and efficient harvesting of B. braunii.

The microalgae Botryococcus braunii is widely recognized as a potentially important biofuel-feedstock whose commercial exploitation is limited by difficulties with its cultivation and harvesting. In this study, two B. braunii strains, Kossou-4 and Overjuyo-3 were successfully cultured at a 500 l-scale for 60-days. Harvesting by bio-flocculation with Aspergillus fumigatus at an optimum ratio of 1:40 of fungus to microalgal culture resulted in up to 98% recovery of biomass in the two strains. Ultimate analysis (C, N, H, S, ash, high heating value) and pyrolysis (analytical and preparative pyrolysis and GC–MS assays) showed that co-harvesting with fungi did not cause any impairment of the feedstock value of the microalgal biomass. This work represents the first report on the successful culturing and harvesting of these strains at a 500 l-scale using bio-flocculation. The use of A. fumigatus represents an efficient and economical method for the harvest of B. braunii for biofuel production.