The Urban Water System - a Future Swedish Perspective

It is argued, that the use of water can no longer be regarded as an almost free commodity. The idea to assess and value the environmental impact of the water use represents a true change of paradigm. The key issue 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 environment has steadily increased the need for better treatment. We need to be prepared for changes in the society by having a readiness manifested as continuing dynamic research environment in this area. Too often the knowledge build-up has been re-active instead of pro-active. •economising resources: wastewater treatment looks and probably should look quite different in densely populated urban areas and in rural areas. Considering resource handling one has to consider already invested capital costs, land use, water re-use, organic and nutrient use and re-use, as well as overall use of energy. •user aspects: technical functionality, economy and liability in different aspects require profound consideration. A sustainable wastewater treatment has to adapt to a local environment and the total resource demand has to be calculated, including a direct environmental impact on receiving waters, air and soil as well as energy consumption and nutrient recycling. Thus, there is an apparent need for. •quantitative performance index: the quest for sustainable development has to be based on objective reasons as well as subjective ones. An integrated performance index is part of a necessary decision making model for the design and operation of wastewater treatment systems. In this index, it is evident that a trade-off should be made between the pursued quality of the process outputs (liquid, solids, gas) and the associated efforts (investments, operation) required to achieve this considering the inputs (wastewater). In order to make this trade-off, however, a common framework is needed to quantitatively compare the different objectives. A metric to judge the sustainability of different options will facilitate a fruitful dialogue between e.g. politicians, ecologists, engineers and economists. Only a truly interdisciplinary approach can help to solve the challenges ahead