Scale-up of Dunaliella salina cultivation: from strain selection to open ponds

Abstract

The microalga Dunaliella salina was studied at the main stages of transition from laboratory to pilot-scale cultivation: strain selection, nutrient medium selection, estimation of influence of physicochemical factors on accumulation of carotenoids and evaluation of the selected strain growing technology at pilot conditions. Dunaliella salina strain IBSS-2 was recognized as promising for commercial cultivation due to the combination of high-production characteristics, environmental stress resistance, and relative easiness of transition to the carotenogenesis stage. The influence of stress factors on the D. salina culture productivity in two nutrient media was estimated. It was shown that light effect combined with nutrients deficiency is the key factor for β-carotene accumulation. The influence of increased irradiance caused the increase of carotenoid content in D. salina cells up to 8%, and increasing irradiance and salinity resulted in carotenoid productivity going up 1.5 times. Testing of D. salina pilot cultivation system demonstrated that productivity at the first cultivation stage was about 6 g m−2 day−1 in both batch and semicontinuous mode. During pilot D. salina cultivation in Crimea, the culture transition to the carotenogenesis stage was achieved both in summer and autumn. The concentration of carotenoids in the ponds was 200 and 600 mg m−2 with a carotenoid/chlorophyll a (Car/Chl a) ratio of 7 and 4.5 in summer and autumn, respectively. The possibility to use natural population of D. salina cells from salterns as inoculum and brine as a nutrient medium base was demonstrated. The study results suggest that the proposed approach can be recommended for D. salina commercial cultivation.