Community sanitation

Definition

The community sanitation regime applies to the areas where the population and/or the economic activities are concentrated enough to make it possible to catch the wastewater and carry it to a treatment plant.

On the one hand, it applies to the agglomerations whose size is greater than or equal to 2,000 PE, and on the other hand, to agglomerations whose size is lower than 2,000 PE, as long as one of the following situations exists inside the agglomeration:

  • there is an existing community treatment plant, or its construction contract was granted before the coming into force of the order;
  • 75% of the sewers exist and are in good condition, or the situation will eventually be such;
  • there are environmental features justifying that the agglomeration should be subject to this sanitation regime.

87% of the population in Wallonia is subject to the community sanitation regime. The vast majority of the population is located in agglomerations of 2,000 PE and more, for which all the water collection and treatment works must be registered to one of the programmes of the SPGE.

In order to complete the sanitation of areas located in agglomerations of less than 2,000 PE, the investment programmes 2005-2009 and 2010-2014 allocate a budget of €175 million that concerns more than 100 water treatment plants. Beyond these programmes, 330 treatment works still need to be built (more than half of them in agglomerations of less than 500 EH).

Currently, nearly 75% of the Walloon population in community sanitation is ‘connected' to an existing treatment plant. When the SPGE was created in 1999, it was only the case of 30% of the population.

General principle

In community sanitation in Wallonia, wastewater is collected by sewers to purify it in a treatment plant.

Sewerage

The sanitation network begins with the connection of the house to the municipal sewage network. The sewerage is designed in the first place for the disposal of wastewater. In Wallonia, the network often drains roof and street rainwater away. We then talk about a “combined sewer system”. When wastewater and rainwater are collected separately, we talk about a “separate sewer system”. In that case, water inside the houses also needs to be separated and connected to the right networks.

Main wastewater sewer

A main sewer collects the wastewater of various sewer networks to bring it to the treatment plant. In the case of combined sewer systems (that is, collecting both wastewater and rainwater), a limiting flow device (storm overflow) is installed in such a way as to bring but a fixed flow to the plant. The overflow is carried away in a nearby stream. The system is calculated so that the water pollution be greatly diluted, and that the aquatic environment may withstand this discharge. In some cases, the overflows are stocked in order to be treated afterwards in basins “of first rain”, or are immediately treated in specific rainwater treatment systems.

Pumping stations

In the sanitation network, water usually flows due to gravity. When the ground is not naturally sloping enough or if an obstacle must be crossed, pumping stations and pressure pipelines are installed to carry the wastewater to the treatment plant. A well-thought-out sanitation network only contains a bare minimum of pumping installations, so as to limit the energy consumption the lifting system needs.

Water treatment plant

The water treatment plant is the most visible part of the sanitation system. Wastewater is treated there, usually following a natural biological process. At the end of the treatment, the purified water is clean enough to be returned to a stream. In Wallonia, water treatment plants produce by no means drinking water.

26/07/2017

See the following pages