Investigation of the Effect of Solar Irradiation and Temperature on H. pluvialis Production in Photobioreactors Under Outdoor Cultivation in Sri Lanka

The complicated and varying weather conditions and contamination from fungi, protozoa, and bacteria are major problems associated with outdoor microalgae cultivation. In this study, outdoor microalgae cultivation was investigated in a 3.2 L vertical tubular photobioreactor in Moratuwa, Sri Lanka. During December, when both the solar irradiation and temperature were high, the water spray system in combination with two agro shading nets (each with a shading rate of 40-50%) could effectively reduce the temperature to $2 \pm 2\ {}^{0}\mathrm{C}$ and control solar irradiation below 13500 lux. Under an initial biomass density of 0.2875 g/L and an atmospheric air flow rate of 1 vvm, Haematococcus pluvialis showcased a maximum biomass accumulation of 0.45 g/L and the maximum productivity of 20 mg/L/day. In addition, the reactor system and its design exhibited good performance, implying a potential scale-up opportunity. However, operation under outdoor conditions showed slightly poorer performance due to the light inhibition effect.