The Swedish research programme Urban Water has developed a concept of a multi-criteria basis intended to support decision-making for urban water and wastewater systems. Five criteria groups were established for sustainability assessment of urban water systems: Health and Hygiene, Environment, Economy, Socio-culture, and Technology. Each criterion requires a set of indicators corresponding to quantifiable facts and figures, or qualitative data to comparatively assess the different alternatives in the decision process. The decision support process starts as a baseline study where the existing conditions are addressed. Alternative strategies of the future urban water system are developed and analysed by different tools and methodologies in assessing the five criteria groups. Eventually, the results and conclusions are integrated and synthesised into a basis for decision-making. As an example of a decision support basis for chemical safety, a barrier perspective was introduced to find out if and to what extent hazardous substances can be stopped, diverged, or transformed at various points in the wastewater system. A set of barriers was suggested, i.e. behaviour, systems design, process design, optional recipients, and organisational. The barrier approach was applied to two alternative municipal wastewater system designs--a combined wastewater system vs. a source separated system--analysing the fate of phosphorus, cadmium, and triclosan. The study showed that the combined system caused a higher substance flow to the receiving waterbody than the separated system. The combined system also brought more phosphorus and cadmium to the farmland than the separated system, but only half the amount of triclosan.
The objective was to outline a process for selecting hazardous substances as pollution indicators that imply a chemical risk for the recycling of wastewater residues on arable land and for wastewater discharge into receiving waters. The reviewed methodologies showed one commonality: grouping of various characteristics that symbolise hazardous properties. From each group, one or several indicator substances were selected to represent the hazardous property of that specific group. The selected set of indicator substances represented the chemical risk characteristics as a whole. One conclusion is that it is difficult to create a comprehensive list of indicator substances for the monitoring of chemical risks in wastewater and residues. Due to the insufficiency of knowledge about the chemical risks from complex systems such as a wastewater system and the methodology for selecting indicator substances, many simplifications have to be accepted. The 100,000 substances present in the technosphere, of which 30,000 are regarded as “everyday” chemicals, may end up in wastewater systems. We have a limited knowledge of many of these substances, thereby providing a weak base for assessing the true chemical risks in wastewater and residues for reuse on arable land. Although the pollution situation will not entirely be understood by measuring the status of only a few substances (important substances may be overlooked), detected substances indicate a specific pollution situation in wastewater or sludge, thus increasing our knowledge about the current concentrations.
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