Samenvatting

Microalgae can produce a wide range of valuable metabolites such as proteins, lipids and pigments, so they can be used in many ways. For aquaculture industry, microalgae are usually used as live feed because of their high nutritional level. Fry Marine(Vlissingen, NL) is a hatchery for marine feed and flatfish, they create a 'food-chain' for their flatfish which starts from cultivating Rhodomonas in photobioreactors. The nutrients (mainly Nitrogen and Phosphorus) that are mainly used for algae cultivation are expensive chemicals, and extra nutrients in the harvest/waste of algae cultivation can be harmful for fish/environment. Since they are artificially added into the medium in continuous systems, it is possible to find a more cost-effective as well as environmentally friendly way to cultivate the algae by optimizing the nutrient application. Previous research on Rhodomonas Baltica has shown that a medium with 0.54 g/L Nitrate and 0.034 g/L Phosphate is for growing the algae with the maximum productivity (0.486 g/L/day) and the minimum waste of nutrients in a continuous system. Based on the results of previous research, this study has demonstrated that cultivating Rhodomonas sp. with a 10x medium (0.54 g/L Nitrate and 0.034 g/L Phosphate) is optimal to achieve the highest productivity of 0.837 g/L/d and leave the least amount of unused nutrients in the harvest. Besides, since it’s known that nitrogen starvation often stimulates the accumulation of carbohydrates and lipids, a medium without nitrogen (N starvation) and another one without phosphorus (P starvation) were applied after the biomass production phase to text their effects on the biochemical composition of Rhodomonas sp. cells. Protein, phycobiliprotein and pigments content in the algae cell were measured every few hours for the phase of N and P starvations, and it was suggested not to apply a period of N starvation after the harvest of Rhodomonas sp. because it would cause decreases on the contents of protein, phycobiliprotein and chlorophyll, P starvation medium can be used to store the algae culture after the harvest because cells could survive in this case without changing their composition.