A closed system for outdoor cultivation of microalgae

Abstract

The main problems in the large-scale cultivation of microalgae outdoors in open ponds are low productivity and contamination. To overcome these problems a closed system consisting of polyethylenes sleeves was developed. In a study conducted outdoors in the Negev area (Beer-Sheva, `En Yahav and Elat) the closed system was found to be superior to open ponds with respect to growth and production in a number of microalgae. In both closed and open systems, growth and production under continuous operation were higher than in batch cultivation. In continuous cultures the respective daily yields of dry matter and polysaccharides from the red microalga Porphyridium sp. were 17.7 and 7.4 g m −2 in the sleeves compared with 7.6 and 2.4 g m −2 in the ponds. With the aim of optimising growth and production the effect of sleeve diameters (10, 20 and 32 cm) on these parameters was investigated. Growth and polysaccharide production were superior in the narrow sleeves than in the wider sleeves. To scale up the system a unit of connected sleeves was developed, and the performance of various microalgae in the unit was investigated. The productivity in terms of biomass and polysaccharide production of the red microalga Rhodella reticulata was higher in sleeve units than in open ponds. β-carotene production by the green microalga Dunaliella bardawil and its isomer ratio (9- cis : all- trans) were better in the sleeve unit than in open ponds. The sleeve system seems to have a significant advantage over open ponds, and its development and optimisation are under way.