The new trend in using photosynthetic microorganisms for the epuration of wastewater in recirculating aquaculture systems (RAS) opens a new question concerning the economic significance of this newly synthesized biomass. In this paper, we present our original results concerning the production of photosynthetic biomass (both prokaryotes and eukaryotes) and associated non- photosynthetic microbiota during the purification process of artificial wastewater. The results present the wet and dry weight quantities of weekly synthesized photosynthetic biomass (with 3 harvesting processes per week). The obtained biomass is analysed with respect to the lipid content, total proteins, as well as carotenes. As our main task is to use this microbial biomass as valuable substrate for fish growth and not for the trivial usage as material for biogas production or fertilizer in agriculture, these results could make a big impact for a better utilization of natural resources, including in the rather new context of circular economy.