Beta-carotene production within Dunaliella salina cells under salt stress condition in an indoor hybrid helical-tubular photobioreactor

For the cultivation of Dunaliella salina (a green unicellular eukaryote photosynthetic microalga), a 20 L indoor helical-tubular photobioreactor was designed. The inner diameter and the thickness of the PU (polyurethane) tube were 12 and 2 mm, respectively, and its length was 75 m. An open pond was located on the top of the PBR structure and a pump circulated the culture medium from the pond to the tubes. Another part of the tube was connected to an airlift column (which was connected to the bottom of the pond), and the culture medium completed its circulation by moving from the airlift column that connected the closed system (tubular) to the open system (open pond). Eight LED lamps with 10 000 lx were set around the tube and a 2000 lx LED was adjusted on the top of the pond. The culture salinity within the PBR was 1 mol L-1 and four intermittent steps of 0.5 mol L-1 salt stresses were injected into the culture medium. The highest beta-carotene production within this hybrid helical-tubular PBR was 4.85 mu g of beta-carotene per mg of dry weight of microalgae at 2.5 mol L-1 salinity.