The purpose of the study was the design of an aerator-oxidizer and optimal parameters of its work to ensure the conditions of mixing and dissolution of oxygen, in which there is no disturbance of the state of activated sludge. The testing of the work of the aeration-oxidation setup of rotor type with the use of a sludge mixture with different design of aerator-oxidizers and in different operating modes was performed. The assessment of the effect of processing on the state of the activated sludge was carried out according to standard parameters: sludge index, chemical oxygen demand. In addition, the number and state of activated sludge organisms were evaluated. The results of qualitative and quantitative analysis of activated sludge before and after processing in the setup are presented. The parameters in which the activated sludge functions in satisfactory mode are revealed.