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A modern city is a place of residence for organisms, human and otherwise, and it can be itself described as the sum of the metabolism of its inhabitants. This idea of investigating a city as an organism which can be studied by modeling the flows entering and going out is quite new and falls within the purview of the emerging specialty of industrial ecology. To be regarded as sustainable, the city's metabolism has to fulfill certain criteria, which cover social, economic and environmental impacts, and which avoid reducing the abilities of future generations to serve their needs as we presently serve ours. Within the different kind of flows that can be studied in a city's metabolism, water flow has a crucial place, as water is one of the fundamental human needs. Recent research has shown that water in urban areas is contaminated by xenobiotics. Many of these substances are of major concern regarding their possible long-term impacts on both humans and the environment. It is therefore vital and urgent to define criteria that allow sustainable urban water management in terms of xenobiotics.
The goal of this study is to define a set of clear and concise sustainable criteria for xenobiotics in the urban water cycle. These criteria have to be related to quantifiable indicators that are easily measured and easily communicable so that they can be used for public information. In a first step, the criteria will be defined to account for human's health as well as aquatic life's preservation. In the future, other criteria (economic, sociological) may be added to the study. These criteria should help to identify problems posed by these substances in water and to formulate solutions to reduce the impact they have.
The study itself is divided into four phases, which cover: the model's formation, the determination of criteria and indicators, the analysis of the city's metabolism (problem identification and solutions) and the model's application to the city of Lausanne. In the future, the results may be applied to other cities.
Due to the great number of xenobiotics in the environment, we will group them according to their sources and their fate in the urban water cycle. For each group, we will choose one or two substances that can be used as representative of the group and for which we can quantify the flows and the impact on both humans and the aquatic environment. Two levels of analyses will therefore be made: a qualitative analysis per group and a quantitative analysis for the representative substances. When problems are identified, we will investigate the solutions to reduce the impact of the substances.
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