THE URBAN WATER-SYSTEM - A FUTURE SWEDISH PERSPECTIVE

It is argued, that the use of water can no longer be regarded as an al most free commodity. The idea to assess and value the environmental im pact of the water use represents a hue change of paradigm. The key iss ue is that any future wastewater treatment system has to be evaluated according to a quantitative criterion. This has to consider: hygienic aspects: we believe that nobody will accept a lower hygienic standard than today. environmental impact: the wastewater impact on the environ ment has steadily increased the need for better treatment. We need to be prepared for changes in the society by having a readiness manifeste d as continuing dynamic research environment in this area. Too often t he knowledge build-up has been re-active instead of pro-active. econom ising resources: wastewater treatment looks and probably should look q uite different in densely populated urban areas and in rural areas. Co nsidering resource handling one has to consider already invested capit al costs, land use, water re-use, organic and nutrient use and re-use, as well as overall use of energy. user aspects: technical functionali ty, economy and liability in different aspects require profound consid eration. A sustainable wastewater treatment has to adapt to a local en vironment and the total resource demand has to be calculated, includin g a direct environmental impact on receiving waters, air and soil as w ell as energy consumption and nutrient recycling. Thus, there is an ap parent need for, quantitative performance index: the quest for sustain able development has to be based on objective reasons as well as subje ctive ones. An integrated performance index is part of a necessary dec ision making model for the design and operation of wastewater treatmen t systems. In this index, it is evident that a trade-off should be mad e between the pursued quality of the process outputs (liquid solids, g as) and the associated efforts (investments, operation) required to ac hieve this considering the inputs (wastewater). In order to make this trade-off, however, a common framework is needed to quantitatively com pare the different objectives. A metric to judge the sustainability of different options will facilitate a fruitful dialogue between e.g. po liticians, ecologists, engineers and economists. Only a truly interdis ciplinary approach can help to solve the challenges ahead. (C) 1997 IA WQ, Published by Elsevier Science Ltd.