4. Methods to limit the pollution of RUTPs and their impacts

4.1 Elements of strategy

When it rains, the city discharges wastewater and runoff, either separately (separate system) or as a mixture (combined system) (figure 10 ). The quantities of water and pollutants discharged during these periods are considerable, and it is no longer possible to consider rainy weather as an exceptional situation during which highly degraded operation of the wastewater system can be tolerated. In application of the European directive on urban wastewater of May 21, 1991