High-density culture of marine microalgae — Promising items for mariculture: III. Mass culture of Monochrysis lutheri Droop

Abstract

Monochrysis lutheri Droop was grown in a 1.5-l culture vessel of the bubbling type with a suspension layer of 15 mm to determine the optimal cultivation conditions, specifically the light regime and nutrient medium. The cultivator was fitted with a thermostat to maintain the temperature at 28°C. Light was provided by a RNaH-400 W lamp. It was found that the lag-phase period of the culture (from 5 to 100–150·10 6 cells/ml) could be reduced by using swine manure as a nutrient medium and increasing light intensity at the surface of the cultivator to 40 klx as the cell number increased. After passing through the lag-phase the Monochrysis culture was grown in a mineral nutrient medium alone and was found to respond favourably to a higher light intensity of 100 klx. On the third day the number of cells in suspension increased to 1.3·10 9/ml at 100 klx and to 0.8·10 9/ml at 40 klx. The culture from the bubbling cultivator was used as inoculum for a 120-l glass tube cultivator illuminated by nine RNaH-400 W and nine RHL-1000 W lamps. During the batch culture period of 5 days, the cell number increased from 50 to 900·10 6/ml, where-upon the cultivator was operated for continuous culture and 50–60 l of the suspension with a cell density of 900·10 6/ml was removed daily. The daily yield from the cultivator was no less than 200 g of dry biomass. It is believed that the productivity of the culture may be increased by increasing the circulation speed of the suspension in the cultivator tubes by a change from indoor to outdoor cultivation.