Pilot plant cultivation of microalga Dictyosphaerium chlorelloides with night illumination from LEDs sources

Illumination during the night with white LEDs increased the growth of the microalga Dictyosphaerium chlorelloides strain CCALA 330 on a thin-film platform unit (150 L volume, 12 m² area) approximately 2.5× in comparison to the platform illuminated only by the Sun. The mean PAR intensity on the Sun-illuminated unit was 71 μmol m⁻² s⁻¹, on the Sun + LEDs unit 549 μmol m⁻² s⁻¹, the mean temperatures were 15 °C and 20.1 °C. On the Sun unit the algae grew to a maximum of 15 g L⁻¹ dry weight in 42 days, with Sun + LEDs into 17.8 g L⁻¹ during 24 days when the both units reached the stationary phase of the growth curve. Biomass production was 3.3 in the Sun and 8.54 g m⁻² d⁻¹ in the Sun + LED, i.e. 0.27 and 0.68 g L⁻¹ d⁻¹. In total, the mean of 37.5 and 58.2 kWh per night were consumed, so the total electricity consumptions for biomass production was 0.20 and 0.40 kWh g⁻¹ DW during LED + Sun cycles 1 and 2, respectively. The production of the extracellular polysaccharides was practically the same for both platforms, and constant during time. A more substantial double increase was only after 30 days of cultivation in both platforms and reached 4 g L⁻¹. The fluorescence measurements proved good physiological state of the cultures. The PAR was found as a main driver of the photosynthetic activity. The correlation of the growth and fluorescence parameters to the environmental conditions was much more profound in the Sun pilot plant, therefore the reliable set of monitored parameters should be defined according to the cultivation type, for both of them we propose OD₆₈₀/OD₇₂₀ ratio as a proxy of nutrient deficiency.