Water quality modelling techniques havebeen used to evaluate and predict the influence of taken, projected and potential sanitation measures for domestic and industrial wastewater loads in the River Rhine drainage area. 15Because of serious eutrophication problems in the Dutch fresh water lakes, that are fed by the River Rhine, special attention is given to the quantification of sanitation measures that can reduce the nutrient concentrations. As a base for modelling the River Rhine water quality, a one-dimensional steady-state model MODQUAL (a modified version of the QUAL-II model) has been developed and applied on the riversystem downstream of Lake Constance, including the main tributaries Neckar, Main and Mosel and the Dutch branches IJssel, Lek and Waal. It is shown that the development of wasteloads and the introduction of biological (secondary) treatment since 1973, has resulted in a significant improvement of water quality components as DO, B0D5, COD, Kjeldahl-N and NH4-N. The influences of tertiary treatment directed on nitrogen or phosphorus removal and the introduction of phosphate-free detergents are quantified for various hydrological conditions.
