A major new trunk sewer was finally completed in Saint Petersburg, Russia in 2014 after 28 years in the making. It now carries nearly all the city's sewage for treatment by way of a 12 km long siphon rather than allowing it to discharge to the Neva River. The sewer's unprecedented design features a number of innovative solutions. A distinctive feature is the unique arrangement of composite construction shaft connections in the pressurised section of the sewer. This paper describes the solutions adopted for removing and treating entrained air, collecting debris and preventing corrosion in the inner structures and tunnels. Alternative solutions for more efficient sewage discharge and treatment are also described. The solutions are applicable to the design and construction of other large-scale urban sewer systems.
The article considers the problem of silting-up of sewage inverted siphons. A review of modern methods of hydraulic flushing is presented. To ensure reliable and energy-efficient operation of the inverted siphon, it is proposed to use the air cushion effect. To ensure the stable operation of the structure, a simulation of the inverted siphon installation was performed, consisting of two sections with nodes for receiving runoff from the drop risers, a node that provides water removal and a node for regulating the pressure in the air cushion. As a result of the simulation, there has been obtained the distribution of the volume fraction of the water phase and the gas phase, the pressure distribution in the horizontal and vertical inverted siphon pipelines and the values of the flow velocity during the formation of the air cushion. The use of separation partition walls at the ends of horizontal siphon pipelines allows creating autonomous air cushions and regulating the work for each section separately. The adaptation of the air cushion inverted siphon technology in relation to the main sewer system is considered to be promising.
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