The study’s objective was to determine feasibility of proliferating algae biomass based on eluate from closed fermentation tank of Municipal Wastewater Treatment Plant in Olsztyn. The eluate originated from retention tank of eluates produced from dehydration of fermented sludges. Experiments were run with race track-type reactor (active volume 1.0 m3) with paddle agitator assuring flow rate of 0.5 m/s, artificial lighting system, valves for eluates dosing, inlet of air or carbon dioxide, and outlet valves, central partition assuring circulation, and heating system. The cultured algae were a mixture of Chlorella sp. (70%) and Scenedesmus sp. (30%) genera phytoplankton. Each day, the reactor was fed with various doses of eluates ranging from 3.0 to 7.0 dm3/day, depending on culture time and algae biomass concentration in model reactor. Resultant biomass was concentrated and removed outside the system using barrel screen with mesh diameter of 10.0 µm. The maximum values of algae biomass concentration oscillated around 850 to 900 mg d.m./dm3 with average growth rate approximating 50 mg d.m./day. During experimental period, the effectiveness of contaminants removal from eluate was very high. For organic compounds characterized by COD value the average removal effectiveness exceeded 98.5%, whilst for total nitrogen – 98.7%, whereas for total phosphorus was the highest and reached 99.4%. The study showed symbiotic growth of biomass of unicellular and filamentous algae and a low number of bacteria. In this artificial ecosystem the algae constituted 80% (37% – Chlorella sp., 18% – Scenedesmus sp., 16% – blue-green algae, 9% – filamentous algae), whereas bacteria - 20%, including small contribution of protozoa. Owing to such proportion achieved in the culture, the biomass had very good sedimentation properties and formed compact conglomerates which could be easily isolated from the culture medium through sedimentation.