The operation of sewage and waste water treatment plants is carried out according to the standards laid down by the Walloon government when it laid down the provisions of European Directive 98/45/EC of 27 February 1998. These treatment plants are designed and adapted so that flow measurements and representative samples of the incoming waste water can be taken, as well as the plant effluent after treatment.
These plants have to be designed, operated and maintained in order to guarantee sufficient treatment capacity to handle all normal climate conditions in the areas where they are established.
The sectoral emission standards for treatment plant output for plants dealing with the collective waste water are directly in accordance with the legislation in force (biochemical requirements for oxygen DB05, chemical requirement for oxygen DCO and suspended matter MES). The whole of the Walloon Region has also been classified as a zone susceptible to eutrophication. From now on all water treatment works for a capacity equal to or superior to 10,000 Inhabitant-Equivalents(IE) will ensure that the treatment includes the elimination of nitrates and phosphorous.