Enhanced biomass and lutein production by mixotrophic cultivation of Scenedesmus sp. using crude glycerol in an airlift photobioreactor

This study presents the mixotrophic cultivation of Scenedesmus sp. using crude glycerol (CG) obtained from lab scale biodiesel unit in an internal loop airlift photo-bioreactor (ALR) for enhanced biomass and lutein production. Prior to reactor studies, shake flask experiments were designed using Taguchi orthogonal array method to evaluate the influence of CG concentration, nitrogen to phosphorus ratio (N/P), and inhibitors concentration (methanol and KOH). Experimental run carried out with 5 g/l CG, 20:1 N/P ratio, 0.5 % methanol concentration, and 7.5 mg/l KOH produced a maximum biomass and lutein productivity of 310.18 mg/(1 d) and 2.25 mg/(1 d) respectively. During the mixotrophic cultivation of Scenedesmus sp. in an ALR, the step-wise addition of CG during the growth phase improved the productivity. The CG concentration of 6 g/l showed highest biomass and lutein productivity of 768 mg/(1 d) and 3.59 mg/(1 d), respectively. Monod and Logistic models were employed to fit the growth data. This study illustrated that the fed-batch strategy and mixotrophic cultivation offer higher biomass and lutein production.