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The article presents an algorithm of making a decision for choosing a technological scheme of wastewater treatment for facilities with a capacity up to 1000 m3/day. There are factors, which help to determine the scheme: plant performance, amount of suspended solids and indicator of wastewater pollution with organic compounds - biological oxygen demand. The best solution according to these parameters can be one or more from 14 considered options of technological schemes, that simplifies and speeds up the process of selecting and designing the main structures of a wastewater treatment plant.

This article presents different aeration systems for biological wastewater treatment, their classification, also advantages and disadvantages of the most common aeration methods - pneumatic and mechanical are described. Also, proposals to reduce the energy consumption of aeration systems by maintaining the optimal range of dissolved oxygen concentration at different points of the aeration tank, depending on its type, have been prepared.

The purpose of the study was to determine denitrification rates during aeration tanks converting to the aero-mode of the nitri-denitrifier with the nitrate recycling. Studies were conducted on an experimental facility with wastewater and activated sludge from one of the sewage treatment facilities of the Udmurt Republic. At the beginning of the experiment, the activated sludge was under anoxic conditions (the mixture was mechanically mixed without aeration), while periodically the mixture was analyzed for nitrate content. Thus, the rate of denitrification during endogenous respiration was determined. Further, waste water was added to the sludge (anoxic conditions were preserved) - simulation of nitrate recycling. According to the results of experimental studies, the calculated denitrification rates were rds = 0.71 ± 0.04 mg N-NO3 / mg of active heterotrophic microorganisms per day on easily oxidizable substrate, on endogenous respiration rde = 0.12 ± 0.02 mg N-NO3 / mg of active heterotrophic microorganisms per day, on difficult oxidizable substrate rdp = 0.12 ± 0.01 mg N-NO3 / mg of active heterotrophic microorganisms per day.