Technological watch

Haematococcus species are rich sources of the antioxidant astaxanthin and have good potential for carbon dioxide reduction. A variety of culture systems for these microalgae are currently in development, but clearly profitable approaches have yet to be reported. Open outdoor culture is currently the only feasible culture system for producing large amounts of biomass. In this study, based on laboratory results, the cultivation of Haematococcus was divided into two stages: a green stage characterised by cell growth, and a red stage characterised by astaxanthin accumulation. For mass culture, we adopted a hybrid open–closed pond system for astaxanthin production. The open culture system was shown to produce approximately 50 kg (dry weight) of biomass per culture at an average rate of 0.51 g L−1, with 0.52 μg mL−1 of astaxanthin content in a 12 -m3 water tank. As large amounts of microalgal bioproducts are in high demand, inexpensive open outdoor culture methods should be adopted as an alternative to costly closed photobioreactors. Although the levels of biomass and astaxanthin production were found to be 30% lower in the field than in the laboratory in this study, the basic data obtained in this research may be useful for lowering astaxanthin production costs.