Change of bacterial water quality in drinking water distribution systems working with or without low chlorine residual

Abstract

Investigations into distribution systems (DS) working without or with low disinfectant residuals showed that the main process for the bacteria change in such systems is the release of bacteria from the biofilm, whereas the growth of bacteria in the water can be neglected. Important for the quality are short-term increases of bacteria release connected to an increase of bacteria growth on the inner pipe surface as a result of changes in the concentration of biodegradable organic matter (BOM) in the water. A model to describe the bacterial water quality change was developed on the basis of investigations. In contrast to other models, a consideration of the formation of BOM as a result of NOM oxidation by disinfectant residuals as well as the decreasing effect of inactivation of released bacteria by the decreasing disinfectant residual concentration, were necessary.

Quantification of the bacterial community of drinking water-associated biofilms under different flow velocities and changing chlorination regimes

“…However, the drinking water chlorination at the range of 0.05-0.42 mg/l free chlorine had stronger influence on the biofilm HPC density than the hydrodynamic conditions. Although the culturable bacteria represent a very small part of the total bacteria number in the drinking waterassociated biofilms, the destabilization of biofilm matrix by the chlorine action and consequent emission of viable bacteria can deteriorate bacteriological quality of drinking water, and as well, cause organoleptic complaints of consumers (Flemming et al 2016;Douterelo et al 2014;Wricke et al 2002). Entering into the drinking water, the culturable bacteria may create serious problems for water consumers' health, especially when some pathogens could survive in the biofilm.…”

“…In drinking water networks, biofilms may cause a number of hygienic and operational problems at water transport and distribution due to the biofilm destabilization and mobilization (Douterelo et al 2014;Flemming et al 2002;Liu et al 2017). Detachment of single cells and small portions of the biofilm or sloughing of larger pieces may increase bacteria numbers in drinking water (Daly et al 1998;Moreira et al 2015;Paul et al 2012;Stoodley et al 2001;Wricke et al 2002). Single cells and small clusters detached more frequently than larger aggregates (Stoodley et al 2001).…”

“…Drinking water disinfection and maintaining a disinfectant residual is a conventional approach to control of bacterial growth in DWDSs (LeChevallier et al 1988;Chen and Stewart 2000;Hallam et al 2001;Tsai 2006;Wricke et al 2002). However, it is well known that the attached bacterial cells exhibit greater tolerance to antimicrobial agents compared to the planktonic counterparts (Bridier et al 2011).…”

Pathogenic Bacteria in Waters and Drinking Water-Associated Biofilms

“…Untreated natural waters are reservoir of obligate pathogenic bacteria and opportunistic ones, such as Aeromonas sp., Acinetobacter spp., Bacillus cereus, Flavobacterium spp., Moraxella sp., Pseudomonas spp., which enter the drinking water as a result of inadequate water treatment for their removal, insufficient disinfection or recovery of the injured cells in the biofilms existing on the surface of pipes and equipment in the drinking water supply systems (DWSS) [7,37,72,76]. Pathogens re-growth in drinking water, their survival or growth in waterassocited biofilms and the accidental contaminations of the water supply systems with untreated or fecal contaminated water due to leakage or mechanical damages of the pipelines are the main reasons for deterioration of the bacteriological water quality [34,37,38,43,68].…”

“…Biofilms are attached microbial communities, ubiquitous in natural waters and purified drinking water [1,18,34,36,72]. Biofilms in drinking waters are object of increasing scientific interest during the last two decades because they represent one of the factors for deterioration of the bacteriological quality of drinking water, however, the provision of clean and safe drinking water in sufficient quantity is a basic human right [19,43,76,77,79].…”