Sewage Treatment for Small Local Authorities: Choice of Process and Recent Trends in France

France has a large number of small rural waste treatment plants. A fairly wide range of technologies suitable for small local authorities has been developed in recent years. The choice of process is now based on a detailed analysis of the limitations imposed by local conditions, with particular regard to those involving the quality objectives for the receiving environment. The main processes used are presented, together with the design basis generally applied. An overview is presented of the situation of France's small treatment plants, through an analysis of a sample of 976 plants with a capacity of less than 2000 inhabitant-equivalents in 11 mainly rural departments covering 13% of France surface area. The distribution of the processes used and the evolution of the choices adopted are analyzed with regard to the size of the plants. The activated sludge process, widely used in all size classes ten years ago, has been gradually replaced by extensive processes, essentially where the capacity is less than 800 inhabitant-equivalents. In some departments, local practices have a great influence over the choice of process.