Effect of culture age and initial inoculum size on lipid accumulation and productivity in a hybrid cultivation system of Chlorella vulgaris

Chlorella vulgaris was cultivated in a hybrid (two-stage) system. The effect of the transferring time from nutrient-replete phase with a low light intensity (photobioreactor) to the nutrient deprivation phase (open pond) with a higher light intensity, as well as the effect of initial cell concentration in the deprivation phase, on the growth rate and lipid content of the microalgae was investigated. The microalgae were transferred to the nutrient deprived medium at different intervals with various initial cell concentrations. Transferring the cultivated medium of the 4th day with the initial cell concentration of 66 mg L−1 into the deprivation phase resulted in a highest lipid productivity of 9.21 ± 0.64 mg L−1 d−1 and lipid content of 53.97 ± 4.30%. In a single-stage cultivation where a medium with nitrogen deficiency was used, despite a low lipid content (maximum 30%), a lipid productivity of 9.95 ± 0.46 mg L−1 d−1 was observed that was slightly higher than that for the hybrid system.