High-density culture of marine microalgae — Promising items for mariculture: II. Determination of optimal light regime for Chlorella sp.f. marina under high-density culture conditions

Abstract

Experiments to determine the optimal light regime for cultivating marine Chlorella were carried out in cultivators of two types: a 2-1 bubbling cultivator with a 15-mm-thick suspension layer, and a circulation cultivator with a 2-mm-thick suspension layer. The batch and continuous cultures were grown in a mineral nutrient medium with the content of nutrients maintained at a stable level of 300 mg N/l, 90 mg P/l, 30 mg Mg/l and 30 mg S/l, at the temperature of 33°C and pH 7.0–7.5. The light sources used were RHL-1000 W and RNaH-400 W lamps as well as sunlight. The radiant energy from different light sources was equalized to provide 2400 W·h −1 per day photosynthetically active radiation (PAR) in the laboratory and 2000–3000 W·h −1 per day PAR in the open air. Higher yields were obtained with natural illumination and with RNaH-400 W lamps. The effect of light intensity on yield was studied with light intensities of 75, 150, 250 and 300 W/m 2 PAR. 250 W/m 2 PAR proved to be optimal at a dry biomass concentration of no less than 0.5 g/l. At this light intensity the maximal daily yield obtained per 1 m 2 of the illuminated surface was 50 g of dry biomass (15-mm-thick layer), the maximal growth rate was 0.1 h −1 and the efficiency of radiant energy utilization was 4%. Results are also presented of growing marine Chlorella under conditions where growth is not limited by light availability.