Mödling WWTP – treatment efficiency and relationship to receiving water quality

The relationship between water protection of small receiving waters and the reliability of treatment efficiency is represented by a 100,000 PE plant. On the basis of stringent emission and immission standards a concept for a one-stage activated sludge plant was developed that meets the current demands on removal efficiency and limit values in Austria with a high degree of reliability. Classic saprobiological analysis of the receiving creek showed saprobic class II. The operation of the treatment plant has been tested in a period of more than two years under normal operational conditions. In this period several modes of operation were investigated and the concept has proved to be successful. A comprehensive data base has been worked up for process comparison and design evaluation. Relevant effluent parameters of a filtration unit in pilot scale are also given. Mass balances for a validation of the data and statistical characterisation of treatment efficiency combined with saprobiological characterisation of the receiving river has proved the applicability to similar cases. These investigations may serve as an example of how to relate treatment efficiency to saprobity of small receiving rivers.