Risk-based evaluations of the hygienic quality of drinking water require accurate data on removal and inactivation of pathogens by different steps of the treatment chain. The continuing trend to reduce chemical disinfection leads to an increased interest in the effect of other processes, based on physical removal or biological inactivation. This study reports data on the removal and inactivation of entero- and reoviruses by three such processes. For comparison, data on a variety of model organisms are also reported. All studies were carried out in the winter period because the concentration of viruses is then at its maximum, and the reducing capacities of the processes are at their minima. Storage in three reservoirs in series (average detention time 7 months) reduced the concentration of enteroviruses by a factor of 400-1,000, river bank filtration was highly effective, reducing enteroviruses by a factor of at least 10,000. The effect of coagulation/flocculation/sedimentation/filtration processes was highly variable, and was better when rapid sand filtration was included. The removal of F-specific RNA bacteriophages most closely followed that of viruses in these three processes.

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