Effect of Distribution System Materials on bacterial regrowth

Abstract

To assess the interactions between pipe materials, organic carbon levels, and disinfectants, studies using annular reactors with ductile-iron, polyvinyl chloride (PVC), epoxy, and cementlined coupons were carried out in the laboratory and at four field sites. Laboratory studies used biologically treated water with and without 0.2 mg/L residual free chlorine or monochloramine, in the presence or absence of 0.5 or 2.0 mg/L humic substances. In the lab studies, the type of disinfectant did not lead to significant differences in effluent and biofilm counts. Increases in carbon led to greater numbers of biofilm and effluent organisms, with the effect most pronounced on iron. Regardless of carbon level, PVC systems typically had the lowest numbers of bacteria, whereas iron had the highest. Cement and epoxy were intermediate. Depending on the site, field studies showed that iron had the highest number of bacteria or there was no difference in materials.olving bacterial regrowth problems (e.g., positive coliforms) has historically been linked to improving source water treatment or optimizing secondary disinfection in the distribution system. Specifically, most water systems have battled their bacterial regrowth problems by increasing disinfectant residual, converting from free chlorine (Cl 2 ) to chloramine, or installing source water treatment processes to decrease the concentration and/or change the nature of the organic matter entering the distribution system. All of these approaches rely on modifying water quality parameters. Another possible solution may be in the rehabilitation or replacement of distribution system infrastructure.A growing body of data strongly indicate that the amount of attached bacteria on iron pipe can be several orders of magnitude higher than on other materials, such as cement linings, polyvinyl chlorinde (PVC), or polyethylene (Niquette et al

Formation of biofilms in drinking water distribution networks, a case study in two cities in Finland and Latvia

“…Corrosion products increase the number of attachment sites for bacteria and decrease the disinfection efficiency, which results in more biofilm. Corroded pipes are known to adsorb organic matter from water and to make it more available for bacteria [6]. This causes an increase in the biofilm density in carbon-limiting waters.…”

Monitoring of Biofilm-associated Legionella pneumophila on Different Substrata in Model Cooling Tower System

“…In addition to biofouling in water system, the dissemination of L. pneumophila may occur over longer distances and may contaminate surrounding inhabitants and adjacent buildings (Dennis, 1988). The characteristics of the surface material greatly influence the densities of biofilm formation (Camper et al, 2003;Pedersen, 1990;Storey & Ashbolt, 2002). A wide range of tower manufacturing materials is used, but generally galvanized steel, stainless steel and concrete are preferred in this field.…”

Microbial Survey of a Full-Scale, Biologically Active Filter for Treatment of Drinking Water

“…Biological processes have the potential to cut operation costs by decreasing the amount of chemicals required for treatment and increasing effectiveness in terms of decreased biological regrowth (e.g., corrosion, nitrification, taste, and odor) in the distribution system (DS) and decreased chlorine demand (6,17,30). However, biological processes have not been widely accepted in drinking water in the United States, mainly due to issues arising from the negative perception of microorganisms as well as questionable reliability and effectiveness (2,8,17).…”