In 2008 volume of treated wastewater was 821.7 mio m³.All in all, 954.101 Mio. m3 was pumped via the municipal sewer system.

Saint-Petersburg has a combined scheme of sewerage: 70% of the whole territory has a combined sewage system, which receives domestic, industrial as well as surface (rainfall, snowmelt) runoffs, the remaining area – mainly, new developments and suburbs sewered according to the separate scheme (rainfall and snowmelt waters are collected separately from other sewage).

The wastewater disposal system is divided into sewerage basins. Discharges of each basin are channeled to corresponding wastewater treatment plants.

The sewerage basins are further divided into sewerage districts, their territories limited by the catchment of big tunnel collectors.

 Sewerage districts are divided into local catchment areas of street sewage systems.

The structure of wastewater disposal sectors is similar to that of water supply sectors.

The Saint-Petersburg wastewater disposal system comprises:

• sewage networks – 7936.4 km
• tunnel collectors – 221.15 km
• sewage pumping stations (SPS) – 109
• wastewater treatment plants of different capacity – 21
• (Krasnoselskaya plant has been temporally taken out of operation after the startup of the South-West wastewater treatment plant and is under reconstruction now).
• sludge incineration plants – 3

Pipe diameters of municipal sewerage network in St. Petersburg are 150 mm (courtyard networks) to 4,7 m (tunnel collectors).

Tunnel collectors are the basic mains for transporting sewage to wastewater treatment plants. In Leningrad the construction of tunnel collectors began in 1947. Inner diameter of tunnel collectors is 2 to 4.7 m, the depth is 15 to 80 m.

The design capacity of sewage pumping stations varies from 300 m3/d to 1,000,000 m3/d. SUE “Vodokanal of St. Petersburg” performs modernization and reconstruction of SPS by implementing modern submersible pump units and integrated sewage pumping stations. In addition to the replacement of pumps and electrical equipment other auxiliary mechanisms are also modernized.

The biggest wastewater treatment plants in St. Petersburg are:

• Central wastewater treatment plant
• Northern wastewater treatment plant
• South-West wastewater treatment plant.

St. Petersburg is the first megalopolis in the world where the problem of wastewater sludge utilization is solved.

Three sludge incineration plants operate in the city – at the Central wastewater treatment plant, Northern wastewater treatment plant and South-West wastewater treatment plant. Sludge is incinerated in the fluidized-bed furnaces at the temperature of 870°C. The heat produced by sludge incineration is used for process needs, space heating and power generation for Vodokanal to save energy resources. Flue gases are treated in three stages.