Combined system of indoor airlift photobioreactor and outdoor raceway pond for the cultivation of Haematococcus pluvialis

Abstract

The cultivation of Haematococcus pluvialis NEIS-144 under controlled conditions was carried out in a two-stage culture system. In the first stage, the cells were maintained in the growth stage in the airlift photobioreactor systems, whereas the second stage was the cultivation under stress conditions in the raceway pond to induce the accumulation of astaxanthin and the cells grew in cyst from. In the first stage, a comparison between the growth of the green vegetative cells was investigated in the airlift systems of two sizes, i.e. 3L with A[subscript d]/A[subscript r] of 2.78 and 17 L with A[subscript d]/A[subscript r] of 3.2. The two airlift photobioreactors gave the maximum cell density of 41x10⁴ and 21x10⁴ cell mL⁻¹, respectively. The optimal conditions for the cultivation of H. pluvialis in the 3 and 17 L airlift photobioreactor were : using F1 medium with pH of 7, illuminated with normal fluorescence lamps at 20 and 30 umol photon m[superscript -2] s⁻¹ and aeration at 0.4 and 1 cm s⁻¹, respectively. A semi-continuous culture of vegetative cells could be achieved where the harvest could be performed at every 4 days. The specific growth rate and productivity in these semi-continuous cultures were 0.179 d⁻¹ and 5.25 cell mL⁻¹ d⁻¹ and 4.75 cell mL⁻¹d⁻¹ in the 3 L and 17 L airlift photobioreactors, respectively. In the second stage, the harvested vegetative cultures were transferred to the high light-intensity at 35-60 umol photon m[superscript -2]s⁻¹ and high salinity at 1-3%wt batch outdoor pond for the induction of astaxanthin. At this stage, H. pluvialis changed from green vegetative cells to non-motile and finally to cysts within 8-9 days. The astaxanthin formation in H. pluvialis seemed to be more rapid at high light intensity whilst the effect of salinity level on astaxanthin induction under the range of salinity employed in this work seemed to be insignificant.