Medium recycling for Nannochloropsis gaditana cultures for aquaculture

Nannochloropsis gaditana is a good producer of proteins and valuable fatty acids for aquaculture. Recycling of culture medium is interesting for microalgae commercial production as it cuts costs and prevents environmental contamination. The recycled medium must be sterilized to prevent the buildup of unwanted metabolites and microorganisms. We tested several sterilization methods: filtration, ozonation, chlorination, addition of hydrogen peroxide and heating. Results showed that the most successful method is ozonation lowering the bacterial load to 1.910(3)CFUs/mL, which is 1000-fold and 10-fold lower than the supernatant obtained after harvesting and the initial filtered medium, respectively. Continuous cultures of N. gaditana were grown using this recirculated supernatant. A maximum biomass productivity of 0.8 g/L/d composed of ∼50% proteins and 40% lipids with more than 3%d.w. EPA was obtained making this biomass very interesting for aquaculture.