During the in situ extraction of ß-carotene from Dunaliella salina, the causal relationship between carotenoid extraction and cell death indicated that cell growth and cell death should be at equilibrium for a continuous in situ extraction process. In a flat-panel photobioreactor that was operated as a turbidostat cell numbers of stressed cells were kept constant while attaining a continuous well-defined light-stress. In this way it was possible to study the balance between cell growth and cell death and determine whether both could be increased to reach higher volumetric productivities of carotenoids. In the two-phase system a volumetric productivity of 8.3 mg ß-carotene LRV-1 d-1 was obtained. In situ extraction contributed only partly to this productivity. The major part came from net production of carotenoid-rich biomass, due to a high growth rate of the cells and subsequent dilution of the reactor. To reach equilibrium between cell growth and cell death, sparging rates of dodecane could have been increased. However, already at the applied sparging rate of 286 Ldod LRV-1 min-1 emulsion formation of the dodecane in the aqueous phase appeared. In a turbidostat without in situ extraction a volumetric productivity of 13.5 mg ß-carotene LRV-1 d-1 was reached, solely based on the continuous production of carotenoid-rich biomass.
- 2-phase bioreactors