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 rote 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 lad by the Méry-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-1. However, no decrease in BDOC is observed when the BDOC in the finished water is lower than 0.16 mgC.L-1. The bacterial abundance in the distribution system is primarily linked to the absence of free chicane. 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-1 in the absence of free chlorine, the highest of these values are in the same range as the growth rates measured for bacteria in natural aquatic ecosystems. Fixed biomass to the inner pipes surface are in the range 0.25 to 0.65 µgC.cm-2 and the average growth rate of fixed bacteria seems to be roughly in the same order of magnitude as the average growth rate of the suspended bacteria. A model of the dynamics of BDOC and bacteria in distribution network, incorporating the knowledge gained from this and previous studies concerning the control of bacterial activity by dissolved organic matter, is presented. It involves a mathematical representation of the kinetics of bacterial adsorption-desorption processes, bacterial attachment, bacterial utilization of biodegradable dissolved organic matter and impact of chlorine on free and fixed bacteria. It allows simulation of the impact of reducing the BDOC in the finished water on processes associated with bacterial regrowth in the distribution network..

A long‐term study identifies the benefits accrued when a distribution system fed with biologically treated water switches to a nanofiltered supply. The authors investigated microbiological behavior of a distribution system supplied initially with biologically treated water and then with nanofiltered water. Their purpose was to identify and evaluate the changes in microbiological water quality attributable to modifications in water treatment at the plant. During the course of the study, all data from various indicators of microbiological quality (i.e., heterotrophic plate counts, coliform enumeration, total direct counts, and fixed bacterial biomass) showed similar trends. Results indicated that the use of nanofiltration allows utilities to reduce chlorination of treated water and at least maintain or increase the microbiological quality of distributed water for areas with high residence times.

More restricting legislation on Dissolved Organic Carbon (DOC) content in drinking water, especially when applied to waters with high DOC contents and low turbidity, urges the industry to improve, all along the processes, the removal of dissolved organic matter (DOM) in drinking water resources. This work focused on the characterisation of the performances of commercially available powdered activated carbons (PAC). Equilibrium isotherms were carried out on pre-treated water, i.e. after coagulation, flocculation and sedimentation. In order to determine the efficiency of the PAC, the DOM content was estimated through DOC and UV absorbance measures, as well as being characterised by size exclusion chromatography. The various experiments carried out showed some differences in the adsorption capacity, depending on their pore distribution and surface chemistry. The maximum removal ratio reached 82% and 45% for DOC and SUVA respectively. The isotherm equilibrium results can be used to define several kinds of DOC fractions, which were modelled by the Freundlich equation. Finally, the SEC chromatograms showed that the pore size distribution of the activated carbons affected significantly the compound size distribution of the removed DOM.

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More restricting legislation on dissolved organic carbon (DOC), especially when applied to waters with high DOC contents and low turbidity, urges the drinking water industry to improve the removal of dissolved organic matter (DOM). Jar tests were carried out on sand-filtered water (SFW) and raw water (RW), with respectively 50 different particulate compounds and different cationic polymers. Analytical measurements of DOC and UV absorbance at 254 nm, as well as a characterisation by size exclusion chromatography (SEC), were performed in order to determine the efficiency of the process. Experiments on SFW showed that activated carbon was the only compound able to remove efficiently the residual DOC remaining after conventional treatments (up to 40% of reduction). Other trials on RW using mixes of ferric chloride (FeCl3) and cationic polymers (polyamines and polyDADMAC) pointed out that the molecular mass and the reticulation ratios have a significant influence on the efficiency of the treatment. Finally, the addition of activated carbons to the previous reagents significantly improved the observed removal efficiencies by similar amounts.