Municipal wastewater is defined as wastewater from households or a mixture of wastewater from households and of industrial origin as well as precipitation water. In the Rhine watershed, and according to latest inventories, 96 per cent of precipitation waters are cleaned in municipal wastewater treatment plants before being discharged into natural running waters.
The pollution of household wastewater is mainly due to the flushing of toilets, kitchen and cleaning water polluted with bacteria, viruses, washing and cleaning agents including dirt and rests of food. It is comparatively easy to almost completely break down these pollutants with the help of micro organisms used in wastewater treatment plants. Also, the nutrient concentration in wastewater may largely be reduced with the help of particular bacteria.
Further substances and micropollutants , such as medicinal products for human use, biodical products and anti-corrosive agents, oestrogens, radiopaque substances, odoriferous substances , complexing agents and industrial chemicals reach the Rhine together with wastewater after its treatment in wastewater treatment plants.