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Factors affecting the permissible limits of sludge mixture circulation rate are given for airlift reactor-clarifier with a suspended layer. The upper limit of the circulation rate is justified as a function of some geometric dimensions of the bioreactor and the hydraulic load on the clarifier to comply with conditions of a suspended layer existence. The lower limit of the circulation rate was obtained on the basis of two conditions: the duration of the active sludge stay in anoxic conditions and the observance of recommended rates in the construction in order to avoid the settling of active sludge. Theoretical and empirical dependences of the maximum permissible values of the circulation rate on the main geometric parameters and on productivity of the airlift reactor-clarifier are presented.

"For the majority of Kazakhstan sewage treatment plants, the issues of modernization and construction of new blocks of wastewater treatment facilities are very relevant, the solution of which involves a comprehensive engineering and technological approach. This article analyzes the level of automation and disadvantages of the project of the second stage of sewage treatment plants (STP) of the State Enterprise «Astana SU Arnasy». The project of biological treatment on the aeration tanks of the second stage of (STP) does not provide for deep cleaning for biogenic pollutants, namely the internal recycling of activated sludge. The volume of the anoxic zone is 18 %, which is not enough for the process of biological dephosphotation. Thus, in order to more effectively achieve high-quality cleaning indicators, it is necessary to provide for a denitrification zone of at least 30 % of the total volume of the aeration tank. Analysis of the main causes of inefficient removal of phosphates at the stage of biological purification showed: insufficient concentration of biological oxygen consumption in incoming wastewater, absence of denitrification process, dephosphotation in the design of the second stage aerotanks and insufficient volume of the anaerobic zone, which is 18 % of the volume of the aerotank. The problems of inefficiency of technological wastewater treatment from phosphates at (STP) in Astana are primarily related to design errors and the impossibility of effective operation of wastewater treatment facilities associated with insufficient automation. Thus, in order to increase the efficiency of the biological treatment facilities of the second stage, it is necessary to carry out a new calculation of the facilities taking into account the processes of nitri-denitrification and biological removal of phosphates, additionally equip with equipment to ensure internal recycling with the allocation of intermediate zones and in the process of retrofitting to provide greater automation to minimize manual labor. "

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