Investigation on models for light distribution of Haematococcus pluvialis during astaxanthin accumulation stage with an application case

Light is an important stress factor for astaxanthin accumulation in H. pluvialis. Hence, the light distribution in the H. pluvialis suspension was investigated with biomass concentration from 0.218 g/L to 2.5 g/L during the astaxanthin accumulation stage. Lambert-Beer model and Cornet model were employed to predict the light attenuation. The result showed that Cornet model could slightly better describe and predict the light distribution in H. pluvialis suspension. Besides, Ea (absorption coefficient) and Es (scattering coefficient) were determined as 0.0126 ± 0.0036 m2/g and 0.223 ± 0.023 m2/g, respectively. Es increased with respect to astaxanthin content, whereas Ea declined with the increase of astaxanthin content. The astaxanthin content was the dominant factor at a relatively low mass concentration of H. pluvialis suspension. Furthermore, experiments were carried out in a 3 L-bubble-column PBR (photobioreactor) and a 12 L-bubble-column PBR. Higher volume-averaged light intensity and lower shear stress in 3 L PBR led to 66.67% higher astaxanthin content and 34.48% higher mass concentration than those of 12 L PBR during the outdoor experiment, respectively.