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          Hot water recirculation systems (RECIRC) are labeled green and are sometimes mandated in local plumbing codes. Previous work conducted under non-optimized operation schemes demonstrated that these systems actually waste energy and water versus standard (STAND) water heater counterparts. Optimization of RECIRC system operation by minimizing pump operation did improve energy efficiency 6–60%, saving consumers 5–140% annually in associated utility costs. However, STAND systems were still more energy efficient than any of the RECIRC systems. With respect to factors that might influence pathogen growth, reducing RECIRC pump operations increased disinfectant residual by as much as 560% as compared to the baseline RECIRC system; however, STAND systems still had 25–250% more total chlorine residual than any of the RECIRC systems. At 60°C operating temperature, STAND systems have 30–230% more volume at risk for pathogen growth (e.g., volume with temp 37–46°C) than any of the RECIRC systems. Thus, in the context of “green” design, RECIRC systems provide a convenience to consumers in the form of nearly instant hot water, at a cost of higher capital, operating and overall energy costs. RECIRC systems have distinct advantages in controlling pathogens via thermal disinfection but disadvantages in control via secondary disinfection residual.

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          Most cited references 9

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          Survival of Mycobacterium avium in a model distribution system.

          A pilot study was designed to examine the impact of nutrient levels, pipe materials, and disinfection on the survival of M. avium in model drinking water distribution system biofilms. Studies showed that the survival of the organism was dependant upon a complex interaction between pipe surface, nutrient levels, and disinfectants. The findings showed that when no disinfection was applied, M. avium could be recovered from biofilms at nutrient levels of 50microg/L assimilable organic carbon. M. avium concentrations were lower on copper pipe surfaces following disinfection with free chlorine as compared to monochloramine. However, due to the interference of corrosion products, chloramination of iron pipe surfaces controlled M. avium levels better than free chlorine. These data demonstrate the significance of pipe materials on the survival of M. avium complex in biofilms. Elimination of competitive heterotrophic bacteria on copper pipe surfaces by the application of disinfection resulted in a population of nearly 100% M. avium. Heat treatment of M. avium biofilms was affected by the pipe composition and organic content of the water. Effluent temperatures >53 degrees C were required to control the occurrence of M. avium in the pipeline system. Although additional studies are required using improved detection methods, the results of this investigation suggest that reducing the biodegradable organic material in drinking water, control of corrosion, maintenance of an effective disinfectant residual, and management of hot water temperatures can help limit the occurrence of M. avium complex in drinking water biofilms.
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            Differential growth of Legionella pneumophila strains within a range of amoebae at various temperatures associated with in-premise plumbing.

            The potential effect of in-premise plumbing temperatures (24, 32, 37 and 41°C) on the growth of five different Legionella pneumophila strains within free-living amoebae (Acanthamoeba polyphaga, Hartmannella vermiformis and Naegleria fowleri) was examined. Compared with controls that actively fed on Escherichia coli prey, when Leg. pneumophila was used as prey, strains Lp02 and Bloomington-2 increased in growth at 30, 32 and 37°C while strains Philadelphia-1 and Chicago 2 did not grow at any temperature within A. polyphaga. Strains Lp02, Bloomington-2 and Dallas 1E did not proliferate in the presence of H. vermiformis nor did strain Philadelphia-1 in the presence of N. fowleri. Yet, strain Bloomington-2 grew at all temperatures examined within N. fowleri, while strain Lp02 proliferated at all temperatures except 41°C. More intriguing, strain Chicago 2 only grew at 32°C within H. vermiformis and N. fowleri suggesting a limited temperature growth range for this strain. Identifying the presence of pathogenic legionellae may require the use of multiple host amoebae and incubation temperatures. Temperature conditions and species of amoeba host supported in drinking water appear to be important for the selection of human-pathogenic legionellae and point to future research required to better understand Legionella ecology. No claim to US Government works. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.
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              Introduction of monochloramine into a municipal water system: impact on colonization of buildings by Legionella spp.

              Legionnaires' disease (LD) outbreaks are often traced to colonized potable water systems. We collected water samples from potable water systems of 96 buildings in Pinellas County, Florida, between January and April 2002, during a time when chlorine was the primary residual disinfectant, and from the same buildings between June and September 2002, immediately after monochloramine was introduced into the municipal water system. Samples were cultured for legionellae and amoebae using standard methods. We determined predictors of Legionella colonization of individual buildings and of individual sampling sites. During the chlorine phase, 19 (19.8%) buildings were colonized with legionellae in at least one sampling site. During the monochloramine phase, six (6.2%) buildings were colonized. In the chlorine phase, predictors of Legionella colonization included water source (source B compared to all others, adjusted odds ratio [aOR], 6.7; 95% confidence interval [CI], 2.0 to 23) and the presence of a system with continuously circulating hot water (aOR, 9.8; 95% CI, 1.9 to 51). In the monochloramine phase, there were no predictors of individual building colonization, although we observed a trend toward greater effectiveness of monochloramine in hotels and single-family homes than in county government buildings. The presence of amoebae predicted Legionella colonization at individual sampling sites in both phases (OR ranged from 15 to 46, depending on the phase and sampling site). The routine introduction of monochloramine into a municipal drinking water system appears to have reduced colonization by Legionella spp. in buildings served by the system. Monochloramine may hold promise as community-wide intervention for the prevention of LD.

                Author and article information

                Journal of Green Building
                College Publishing
                Spring 2013
                : 8
                : 2
                : 73-89
                Author notes
                aCorresponding Author: Metropolitan State University of Denver, Campus Box 22, P.O. Box 173362, Denver, CO, USA 80202, rbrazeau@ , 303-556-2699 (p); 00-1-303-556-4436 (f)

                bVirginia Tech, 418 Durham Hall, Blacksburg, VA, USA 24060, edwardsm@

                ©2013 by College Publishing. All rights reserved.

                Volumes 1-10 of JOGB are open access and do not require permission for use, though proper citation should be given. To view the licenses, visit

                Page count
                Pages: 17
                RESEARCH ARTICLES


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