The sewage system

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Urban effluent:

Urban effluent is comprised of sewage and rainwater.

The main objective of sewage purification is to ensure that discharge is made compatible with the protection and preservation of the receiving environment.

- Domestic sewage  comprises : Sewage (from toilets) and "grey" water (from household activity)

- Industrial sewage:

is specific to the sector : abattoirs, dairies, etc. Each has its own characteristics, which often require specific treatment processes.

- Rainwater comprises rainwater, washing water and drainage water

Collection of urban effluent is performed by a network of pipes in continuous operation

 The two main collection systems are: 

  • The combined (sewer) system  which collects urban effluent in the same pipes; it functions in such a way that part of the effluent collected in wet weather flows straight into the natural environment (river, sea, etc.)Only part of the effluent is directed to the purification plant.
  • The separate system made up of two networks of pipes : one for rainwater, the other for sewage, and much smaller in size (diameters). This system directs the sewage to the purification plant and the rainwater into the natural environment.

The main requirement of the collection system is to transport the effluent without disruption and to be watertight to avoid the intrusion of extraneous water.

The transport of effluent to the purification plants is carried out using gravity whenever possible, but it is sometimes necessary to use pumps installed at the pumping stations to discharge the effluent into pressurised pipes, sometimes of considerable length.

In Vannes

Vannes town council has opted for the principle of a separate network for the collection of urban effluent.

Until 1966, it had a rather heterogeneous sewer system, built up of mains of various shapes and diameters, and around 25 km in length.This network, which was actually a rainwater network, collected rainwater as well as sewage. Everything used to flow into streams without treatment which then entered the Gulf of Morbihan, either via the Port of Vannes or through other outlets.

Sewage collection system:

Vannes' sewage evacuation system was begun in 1966, with the installation of main sewers that crossed the town from north to south, enabling the connection of town centre, then in the process of urbanisation, particularly in the Ménimur area.

Since then, the network has spread in line with urban development.The length of the sewage system is now 231 km.

These infrastructures have made it possible to achieve a sewage system connection rate for the people of Vannes of close to 98%.

Transportation of the sewage collected to sewage works is carried out by gravity or by pumping.

Vannes has ten pumping stations, equipped with pumps that discharge the sewage into pressurised pipes leading to the sewage works.



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