At the end of 1997, an innovative membrane-adsorption process was integrated at the Vigneux-sur-Seine water treatment plant in the southeast suburbs of Paris, France. This hybrid process consisted of the application of powdered activated carbon (PAC) upstream of ultrafiltration (UF) membranes and recycled to a floc blanket reactor (FBR) after membrane backwashes (FBR-PAC/UF process). This process was designed to mitigate seasonal episodes of micropollutants (pesticides and taste and odors) and to reduce the content of natural organic matter responsible for disinfectant and disinfection by-products. An intensive monitoring campaign of the plant effluent and ten sites in the distribution system was conducted two years before (1996-1997) and two years after (1998-1999) the start up of the PAC/UF process to characterize the impact of this treatment on the water quality of the distributed water. The objective of this paper is to illustrate the positive impact of the PAC/UF process on the organic and biological water quality of the Vigneux-sur-Seine distribution system. Thus, the combination of coagulation and adsorption in the FBR-PAC/UF process resulted in a TOC concentration lower than 0.7 mg/l, BDOC values lower than the detection limit (<0.2 mg/l) and total trihalomethanes concentrations below 10 μg/l. This reduction in organic content results in a reduction of the chlorine consumption by the water produced, which translates in the maintenance of higher chlorine residuals throughout the distribution system while using the same chlorine doses at the plant (0.3 mg/l).

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