Biomass production and identification of suitable harvesting technique for Chlorella sp. MJ 11/11 and Synechocystis PCC 6803

Microalgae that can grow fast and convert solar energy into chemical energy efficiently are being considered as a promising feedstock of renewable biofuel. Mass production of microalgal oil faces a number of technical barriers that make the current production of biodiesel economically unfeasible. Small size (≈1-20 μm) and negatively charged surface of the microalgal cells pose difficulties in the process of harvesting. This leads to significant increase in the overall cost of biomass production. The present study explored different methods and conditions for harvesting of Chlorella sp. MJ 11/11 and Synechocystis PCC 6803. A customized air-lift reactor was used for the cultivation of biomass under photoautotrophic condition. Significant improvement in the rate of productivity of biomass was observed. Maximum biomass productivity of 0.25, 0.14 g L-1 d-1 for Chlorella sp. MJ 11/11 and Synechocystis PCC 6803, respectively, were obtained. Various flocculation techniques viz. auto-flocculation, inorganic, chitosan and electrolytic flocculation were used for the recovery of biomass. Among all the techniques, electro-flocculation showed high flocculation efficiency (98 %) and floatation of floc causing easy harvesting. Moreover, low-cost and easy control of the process justify electro-flocculation as a most suitable and promising technique for the recovery of microalgal cells.