Utilization of wastewater from the recirculating aquaculture system to obtain Spirulina Platensis biomass for fish food

The paper presents the experimental results obtained when cultivating the cyanobacterium Spirulina platensis on media with the addition of wastewater from the recirculating aquaculture system (RAS) in concentrations of 10%, 30%, 60%, 90% and 100%. Research has shown that the most optimal variant of cultivating cyanobacteria on RAS wastewater is the 10% one, which contributes to obtaining 1.041 ± 0.023 g/l of absolutely dry biomass in 11 days, to accelerating the reproduction rate (0.218 ± 0.002 days?¹) and the reproduction coefficient (1.652 ± 0.023 g/l). The pH values showed that, with the increase in the concentration of wastewater in the nutrient cultivation medium, their increase is observed, reaching up to 12.17 in the variant with 100% wastewater. The increase in the concentration of waste water in the nutrient medium for cyanobacteria cultivation causes morphological changes in the filaments, characterized by elongation. Biochemical analyses indicate that the highest amount of biologically active substances is recorded in the biomass cultivated on 10% RAS and that the biomass can be used in fish nutrition.