Dynamic modelling of Haematococcus pluvialis photoinduction for astaxanthin production in both attached and suspended photobioreactors

Haematococcus pluvialis is a green algae with the great potential to generate natural astaxanthin. In the current study, dynamic models are proposed to simulate effects of light intensity, light attenuation, temperature and nitrogen quota on cell growth and astaxanthin production in both suspended and attached photobioreactors, which to the best of our knowledge has not been addressed before. Based on the current models, optimal temperatures for algal growth and astaxanthin accumulation are identified. Cell absorption is found to be the primary factor causing light attenuation in the suspended reactor. In this reactor, astaxanthin accumulation is limited by the low local light intensity due to light attenuation during the initial operation period, but almost independent from that once it is close to the maximum value. Compared to the suspended reactor, light attenuation in the attached reactor is much reduced and biomass growth is remarkably enhanced, which suggests that the attached reactor is a better choice if the process aims for biomass cultivation. However, the well-mixed culture in the suspended reactor can push most cells toward astaxanthin production; while the attached reactor has the potential to prevent the accumulation of astaxanthin in the bottom algae. Therefore, the suspended photobioreactor should be selected if the process target is astaxanthin production.