Nutrient removal in the river basin of the Ruhr--a German case study

In the catchment area of the Ruhr, restructuring and upgrading measures in the domain of wastewater and stormwater treatment have been under way since 1990 to successively implement the currently applicable legal requirements for nutrient removal. With 2.1 million inhabitants and a design capacity of 3.7 million population equivalents (PE), it is expected that approximately DM 2 billion still have to be invested from 2000 onward. With this it will be possible to further cut the nutrient load in the Ruhr River, that has been declining consistently since the 1970s: by about 25% for Ntotal and about 10% for Ptotal. The anticipated decrease in ammonia-nitrogen in winter is particularly important for drinking water production from the river water (bank filtration). Whether and to what an extent the expected decline in phosphorus concentrations will curb eutrophication in the Ruhr with its several impounded stretches remains to be seen. Further nutrient load reductions cannot be achieved by sewage treatment-related measures. Load balances underline the adverse impact of diffuse or non-point sources, in particular, for nitrogen. Some potential to further improve the situation is seen in minimizing the nutrient releases from agricultural practices.