Effects of harvesting method and growth stage on the flocculation of the green alga Botryococcus braunii

Flocculating activity was determined to evaluate the effective harvesting method and an optimal growth stage for the recovery of the green alga Botryococcus braunii growing in batch cultures. Flocculating activity was highest at 2 weeks of incubation, regardless of harvesting methods. The degree of flocculation was different with harvesting methods and growth stages. A high pH value (pH 11) was more effective for flocculation than treatment with aluminium sulphate or a microbial flocculant, Pestan, until the third week of incubation. The lipid content of the algae on a dry weight basis was unaffected by harvesting methods. These results indicate that the most effective harvesting method is to adjust pH to 11 after 2 weeks of incubation.