Designing a CO 2 supply strategy for microalgal biodiesel production under diurnal light in a cylindrical-membrane photobioreactor.

A cylindrical membrane photobioreactor with high CO2 mass transfer coefficient was designed and installed under customized unidirectional lighting. Combinatorial effect of light and CO2 on the growth of Chlorella sp. FC2 IITG was studied and an optimal CO2 supply without pH control strategy was developed under diurnal light similar to sunlight (17-2000-17 µE m-2  s-1 ). Unprecedentedly, broad range of saturated light levels (700-1500 µE m-2  s-1 ), reversible photoinhibition, no pH control requirement and dark-phase growth were noticed altogether in the strain. Under diurnal light, final biomass titer of 5.79 g L-1 and overall biomass productivity of 1.29 g L-1  day-1 were observed. The results were similar to optimal light (1130 µE m-2  s-1 ) and CO2 (2%) conditions. Subsequently, a highest FAME productivity of 265 mg L-1  day-1 was observed in last two days of lipid induction phase.