Modeling of astaxanthin production in the two-stage cultivation of Haematococcus pluvialis and its application on the optimization of vertical multi-column airlift photobioreactor

Abstract In the current study, a model was proposed to simulate the effects of the outdoor average temperature and average light intensity on astaxanthin accumulation. To this end, two-stage cultures of Haematococcus pluvialis were carried out in an indoor 50 L fermenter and outdoor 3 L column bubble photobioreactors (PBR) in Kunming. The model was then validated with additional outdoor experiments in the 3 L PBRs in Shangri-La and a vertical multi-column airlift photobioreactor (VMAPBR) in Kunming. Based on this, the VMAPBR was further optimized for initial dry cell weight, geometry, orientation and ground reflectivity. Orthogonal tests and range analysis were conducted and the results showed that the optimal group was achieved by 0.06 m in tube diameter, 0.08 m in tube distance, 0.3 in ground reflectivity, 1.2 g L−1 in initial dry cell weight and south-north in orientation. Under optimal conditions, areal astaxanthin productivity of 203,110 mg m−2 year−1 in the outdoor VMAPRB was obtained, which is 45.56% higher than that obtained in an outdoor 25,000 L PBR combined with raceway ponds reported in another study.