Microalgae harvest influences the energy recovery: A case study on chemical flocculation of Scenedesmus obliquus for biodiesel and crude bio-oil production

In the present study, centrifugation was used as a standard harvest method, while chemical flocculation was comparatively used as a cost-effective harvest method for microalgae. Lipid recovery from the centrifuged cells was 17.4%, which significantly increased by flocculation to 20.7%. Although both harvest methods showed similar thermal decomposition patterns, flocculated biomass showed 15.7% higher bio-char formation than the centrifuged cells, which resulted in significant reduction in the bio-oil yield by 18.5%. The estimated energy output of bio-oil using centrifugation and flocculation were 0.87 and 0.68 GJ per ton, respectively. For biodiesel production, the energy output using centrifugation and flocculation were 0.177 and 0.211 GJ per ton, respectively. Due to the higher biodiesel yield, better bio-oil quality and lower energy consumption, flocculation was suggested by the present study as a superior method over centrifugation for microalgae harvest from the economic point of view.