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Distributed Water Quality after 3 Years of Nanofiltration

par Cotte, M.;Pele, B.;Gatel, D.;Cavard, J.;Servais, Pierre
Référence Water Quality Technology Conference(November 10-14, 2002: Seattle, Washington, USA), 2002 Water Quality Technology Conference, American Water Works Association, Ed. CD-ROM edition
Publication Publié, 2002-11-01

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Résumé :

Producing biologically stable water is difficult because finished water still contains Dissolved Organic Carbon (DOC) and bacteria, both of which allow biofilm accumulation in distribution systems. Moreover, the reaction of chlorine with DOC also allows the formation of trihalomethanes (THMs) at the end of the treatment and in the network. Due to its small pore size, Nanofiltration allows a much higher removal of DOC than conventional processes. Hence, the level of DBP precursors and biodegradable DOC (BDOC) are reduced. On this basis, the Suburbs of Paris Utility decided to implement a large surface water nanofiltration unit to improve the quality of its distributed water. At the Méry-sur-Oise Water Treatment Plant (90 MGD capacity), Nanofiltration was put in service in fall 1999 as a refining step after flocculation, ozonation and dual media filtration. The distribution system of the northern suburbs of Paris, now fed with a blend of nanofiltrated water (70%) and conventionally produced water (30%) is a large network with many storage tanks and booster chlorination units, delivering the water to over one million people. A going research project was set to document the impact of such a change on the water quality, over a period of five years (2 years before and 3 years after nanofiltration). Water quality parameter was followed on 15 sampling stations (public distribution system and service lines) include fecal indicators, Total bacteria Direct Counts (TDC), Viable bacteria Counts (VC), DOC and BDOC. Physico-chemical parameters include THMs, chlorine residual, turbidity and temperature. This paper presents and discusses data obtained during this survey.