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Real-time management and operation of an urban sewage system in relation to the quality of the natural environmento (PISYS)
Date du début: 26 nov. 2001, Date de fin: 31 oct. 2005 PROJET  TERMINÉ 

Background The Metz urban area in the East of France (Moselle) has a population of 230,000. It operates a water purification plant which conforms with European standards. However, the water quality of the Seille river, which flows through the city, regularly suffers during low periods. It is a fragile river with a low flow, receiving the overflows from the combined networks of the old town centre. Several installations have been set up to improve the situation and others are planned, including a collector tunnel which will drain the overflow from unitary collectors. In order to operate this equipment, periodic effluent analyses are insufficient. Real time information on the state of the natural environment and the quality of collected water is needed. Objectives The general objective of the PISYS project was to demonstrate the environmental benefits related to the real time management of the flows in the treatment networks of an urban area based on a management strategy that included real time monitoring of the condition of the receiving medium and the quality of the effluent. The principle was to be demonstrated in the greater Metz area. The following results were expected: - Better protection of the natural environment (upgrading of the water quality of the river Seille from class 3, mediocre, to class 2, acceptable). - Safer purification networks so that, in the case of accidental pollution, both the quality of the release to the natural environment, and the quality and harmless nature of the by-products (particularly the mud) are maintained. - Better flow regulation in periods of rain, with reduced hazards in terms of safety and hygiene, both for the operators and the population. The project was to comprise four phases: 1. The installation of measurement stations on the river Seille up to its confluence with the Moselle, and measurement and alert stations at strategic points on the treatment network. 2. Validation and processing of data to assess the impact of the water released into the natural environment and to provide a warning in the case of station malfunction. 3. Implementation and assessment of the proposed strategies, including feasibility study on extending this type of approach to another urban area, Saarebrücken (Germany). 4. Dissemination of the experience acquired, with the publication of a decision-makers guide for sanitation systems operators and a technical, economic, and environmental analysis of the control concept. Results The PISYS project has achieved its objectives and the results are satisfactory. The most significant are as follows: - Six measurement stations and nine alert stations were installed and are operational on the river Seille and the treatment network. These stations are installed in compact metal cabinets and comprise an air conditioner, a pump, measurement probes and instruments and a data transmission module. The probes are continuously measuring flows and physical-chemical parameters, the peak values of which generally indicate pollution. The values are sent through a telephone link to the Haganis centralized management centre. When these values go outside predefined tolerances, a sample of the effluent is automatically taken and an alert is raised. The analysis laboratory can then precisely identify the pollution agents concerned and the technicians can decide whether to direct the water to the treatment station, or to a pollution reservoir. - A sophisticated modeling software (MOUSE) was developed by the Danish Hydraulics Institute (DHI) to represent the transit flows in dry and rainy weather and the impact of the concentrations on the natural environment. A database (using EMMA validation software) was constructed to record the various parameters and ensure the transfer of the corresponding values to the MOUSE model. - The transferability of PISYS concept to the Saarebrücken urban area was studied. The Zentraler Kommunaler Entsorgungsbetrieb (SKE) identified three sites within its urban area for which a collection system optimization analysis was conducted with a view to protection of the natural environment. The German operators were considering equipping these sites with continuous quality measurement stations to enable real time control. In the Saarebrücken context, the problem is that certain streams or small lakes lack water during the summer. The objective would be to supply these streams and lakes using residual water treated by simply decanting or a reed filter system. In order to preserve the reeds during periods of drought, a PISYS type station would allow water of sufficient quality to be taken from the decanter, thus maintaining the biological filter. The cooperation between the French and German partners was expected to continue after the LIFE project. - An interactive CD-Rom, which presents the results of the PISYS project, the analysis of the Saarbrücken urban area and a methodological guide, was produced. The cost of material to run the 15 stations amounts to €24,000 per year and maintenance represents one full time employee. The beneficiary, Haganis, had plans to construct a interceptor collector in the river bed. This project, which is part of the river Seille quality recovery action, is to intercept, in rainy weather, single releases in Metz. In light of the PISYS project, new variants of the inceptor were being studied. It will only be possible to realistically assess the improvement of the quality of the river Seille and the existence of safer purification networks after the installation of this interceptor collector in the river bed.


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