Modelling of water quality-based emission limits for industrial dischargesin rivers

Water authorities apply a diversity of models and input data to set water q uality-based emission limits in discharge permits. To illustrate the conseq uences of model and data selection, two complete mixing models and four mix ing zone models used in Germany, the United Kingdom (UK), the Netherlands a nd the United States of America (USA) were selected and applied to various discharges of cadmium. The maximum allowable annual cadmium load was calcul ated for each model and diverging input data for upstream flow, upstream co ncentration, effluent flow and effluent concentration. Due to model selecti on, differences in pollutant loads amounted to a factor 3. Harmonisation of the derivation of water quality-based emission limits is necessary to prev ent widely divergent pollutant loads under comparable environmental conditi ons. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.