Effect of LED Illumination Cycle and Carbon Sources on Biofilms of Haematococcus pluvialis in Pilot-Scale Angled Twin-Layer Porous Substrate Photobioreactors

Light-emitting diodes are increasingly used as artificial light sources in Haematococcus pluvialis cultivation due to the fact of their energy advantages. The immobilized cultivation of H. pluvialis in pilot-scale angled twin-layer porous substrate photobioreactors (TL-PSBRs) was initially performed with a 14/10 h light/dark cycle and showed relatively low biomass growth and astaxanthin accumulation. In this study, the illumination time with red and blue LEDs at a light intensity of 120 µmol photons m^-2 s^-1 was increased to 16-24 h per day. With a light/dark cycle of 22/2 h, the biomass productivity of the algae was 7.5 g m^-2 day^-1, 2.4 times higher than in the 14/10 h cycle. The percentage of astaxanthin in the dry biomass was 2%, and the total amount of astaxanthin was 1.7 g m^-2. Along with the increase in light duration, adding 10 or 20 mM NaHCO₃ to the BG11-H culture medium over ten days of cultivation in angled TL-PSBRs did not increase the total amount of astaxanthin compared with only CO₂ addition at a flow rate of 3.6 mg min^-1 to the culture medium. Adding NaHCO₃ with a 30-80 mM concentration inhibited algal growth and astaxanthin accumulation. However, adding 10-40 mM NaHCO₃ caused algal cells to accumulate astaxanthin at a high percentage in dry weight after the first four days in TL-PSBRs.