Continuous cultivation of lipid rich microalga Chlorella sp. FC2 IITG for improved biodiesel productivity via control variable optimization and substrate driven pH control

•Novel twostage chemostat was demonstrated for enhanced biomass & lipid productivity.•Enhanced biomass productivity was achieved by control variables optimization.•Biomass productivity of 92.7 g L−1 day−1 was achieved in the first reactor.•Intracellular lipid enrichment was achieved by acetate addition in second reactor.•An improved lipid productivity of 9.76 g L−1 day−1 was observed in the 2nd reactor.

A novel two-stage continuous heterotrophic cultivation of Chlorella sp. FC2 IITG was demonstrated for enhanced lipid productivity. Initially, effect of control variable e.g. dilution rate and feed stream substrate concentrations on biomass productivity was evaluated. This showed significant variation in biomass productivity from 2.4 g L−1 day−1 to 11.2 g L−1 day−1. Further, these control variables were optimized by using multi-nutrient mechanistic model for maximizing the biomass productivity. Finally, continuous production of lipid rich algal biomass was demonstrated in two sequential bioreactors for enhanced lipid productivity. The biomass productivity of 92.7 g L−1 day−1 was observed in the first reactor which was operated at model predicted optimal substrate concentrations of feed stream. The intracellular neutral lipid enrichment by acetate addition resulted in lipid productivity of 9.76 g L−1 day−1 in the second reactor. Both the biomass and lipid productivities obtained from current study are significantly high amongst similarly reported literatures.

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