Studies of BDOC and bacterial dynamics in the drinking water distribution system of the northern Parisian suburbs

Abstract

The deterioration of water quality in distribution systems due to bacterial regrowth is, at the present time, a major concern of drinking water producers. In this context, a good knowledge of the factors controlling bacterial development is required; the aim of the present study is to understand the role of biodegradable dissolved organic carbon (BDOC) in the bacterial dynamics of the distribution system. This paper discusses the results obtained in a study carried out in order to assess the dynamics of biodegradable dissolved organic carbon and suspended bacteria in the water distribution system of the Northern Parisian suburbs fed by the Mery-sur-Oise treatment plant. The results show clearly that a significant decrease in BDOC occurs within the smallest pipes, when the BDOC level in the finished water is higher than about 0.20 mgC.L "SUP -1" . However, no decrease in BDOC is observed when the BDOC in the finished water is lower than 0.16 mgC.L "SUP -1" . The bacterial abundance in the distribution system is primarily linked to the absence of free chlorine. Temperature and BDOC concentration in the finished water are also major controlling factors of bacterial numbers. Bacterial growth rates are in the range 0.005 to 0.1 h "SUP -1" in the absence of free chlorine the highest if these values are in the same range as the growth rates measured for bacteria in natural aquatic ecosystems. (Authors)