The waters in some of the community water‐supply systems in the US often contain a myriad of microorganisms that carry past the disinfection barrier. Although the majority of those that survive and flourish are not pathogenic, the situation presents a potential danger. Here is an article on the sort of organisms that contribute to the trouble, with a description of factors relating to propagation of the species.
Colonization of microorganisms and resultant high bacterial populations often occur on or within protective encrustations or tubercules inside a distribution system. Formation of these encrustations is affected by a variety of physical, chemical, and biological activities within the pipes, which can be examined in situ by scanning electron microscopy (SEM). SEM photographs demonstrate graphically the survival of microorganisms in the distribution system and their possible role in tubercle formation.
Aims: To evaluate throughput of seeded Legionella pneumophila bacteria in domestic point‐of‐use filters.
Methods and Results: The filters were challenged with tap water seeded with Leg. pneumophila. After multiple challenge events (4·25 × 1011 CFU per filter), the levels of Legionella were lower in the effluent from the filter containing both copper and silver (mean 4·48 × 103 CFU ml−1) than in the effluent from the filter containing copper only (1·26 × 104 CFU ml−1; P < 0·001). After a single challenge event of approx. 5 × 109 CFU L. pneumophila per filter, there was no significant difference between the levels of Legionella in the effluents from a carbon filter containing copper and a carbon filter with no metals (mean 6·87 × 102 and 6·89 × 102 CFU ml−1, respectively; P = 0·985).
Conclusions: Legionella was detected in filter effluent up to 6 weeks after being challenged, indicating that while filters may reduce the levels during an initial contamination event, the exposure is extended as the accumulated bacteria slough off over time.
Significance and Impact of the Study: This study has provided an understanding of the response of Legionella to the use of silver and copper in domestic point‐of‐use carbon filters.
Point‐of‐use water treatment devices were investigated to identify organisms that may colonize these filters, to determine the magnitude of the postcolonization release of microorganisms into the product water during daily use or after periods of nonuse, and to demonstrate the effect of tap water of marginal bacteriological quality on the quality of the product water. The bacterial count was found to vary between units of different design, between units of the same design, and between water samples from the same filter unit collected at different times of the day; it was affected by the length of time the filter cartridge had been in use, the design of the cartridge, and the temperature of the water, as well as by the species of microorganism.
Consumers are buying and installing point-of-use carbon filtration devices at an increasing rate, with little or no guarantee of their advertised efficacy for water quality improvement, and no knowledge of the possible bacterial growth that may occur within the granular activated carbon cartridge.
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