PROCEEDING - WATER DISTRIBUTION SYSTEMS ANALYSIS ——————————————————————— OPTIMIZING DISINFECTION STRATEGY IN THE NETWORK AFTER A DRAMATIC IMPROVEMENT OF THE WATER QUALITY LEAVING THE TREATMENT PLANT

To improve and make the finished water quality more reliable, the upgrading of the Vigneux sur Seine treatment plant was decided in 1996 and completed in 1997. Located in the Southeast of Paris, the Vigneux sur Seine treatment plant with a capacity of 55,000 m 3 /day provides potable water to at least 200,000 inhabitants. Measurement campaigns have already been performed at the treatment plant and on the network (10 sampling sites) before and after the implementation of CRISTAL  process to define the impact of this new treatment. They shows that CRISTAL  process leads to a decrease of more than 50% for TOC to reach values below 1.0 mg/l and BDOC around 0.2 mg/l in the network. TTHM decrease also by 10 (average value around 5 µg/l). A reduction of water chlorine demand by more than 2 is also noticed and leads to higher chlorine residuals in the network. The next step of this study is to adjust the existing chlorination strategy to this new water quality. Because bacterial regrowth phenomena in distribution systems are mainly under control of chlorine residuals and BDOC concentration, only water quality modeling can give us some indications on the combined effect of BDOC and chlorine residuals on water quality evolution in the network, by combining chlorine decay and bacterial regrowth (PICCOBIO) modeling. These models have been used in order to define a new chlorination strategy.