Can free chlorine residuals entering building plumbing systems really be maintained to prevent microbial growth?

Autor: Grimard-Conea M; Department of Civil Engineering, Polytechnique Montreal, Montreal, QC H3C 3A7, Canada. Electronic address: marianne-2.grimard-conea@polymtl.ca., Bédard E; Department of Civil Engineering, Polytechnique Montreal, Montreal, QC H3C 3A7, Canada. Electronic address: e.bedard@polymtl.ca., Prévost M; Department of Civil Engineering, Polytechnique Montreal, Montreal, QC H3C 3A7, Canada. Electronic address: michele.prevost@polymtl.ca.
Jazyk: angličtina
Zdroj: The Science of the total environment [Sci Total Environ] 2024 Aug 20; Vol. 939, pp. 173651. Date of Electronic Publication: 2024 May 29.
DOI: 10.1016/j.scitotenv.2024.173651
Abstrakt: Secondary disinfection aims to prevent microbial regrowth during distribution by maintaining disinfectant residuals in water systems. However, multi-factorial interactions contribute to free chlorine decay in distribution systems, and even more so in building plumbing. Assembling 1737 samples from nine large institutional buildings, a meta-analysis was conducted to determine whether building managers can actively rely on incoming free chlorine residuals to prevent in-building microbial amplification. Findings showed that free chlorine concentrations in first draws met the 0.2 mg/L common guide level in respectively 26 %, 6 % and 2 % of cold, tepid and hot water samples, whereas flushing for 2-60 min only significantly increased this ratio in cold water (83 %), without reaching background levels found in service lines. Free chlorine was significantly but weakly (R≤ 0.2) correlated to adenosine triphosphate, heterotrophic plate count and total and intact cell counts, thus evidencing that residuals contributed to decreased culturable and viable biomass. Detection of culturable Legionella pneumophila spanning over a 4-log distribution solely occurred when free chlorine levels were below 0.2 mg/L, but no such trend could be distinguished clearly for culturable Pseudomonas aeruginosa. Water temperatures below 20 °C and >60 °C also completely prevented L. pneumophila detection. Overall, the majority of elevated microbial counts were measured in distal sites and in tepid and hot water, where free chlorine is less likely to be present due to stagnation and increased temperature. Therefore, building managers cannot solely rely on this chemical barrier to mitigate bacterial growth in bulk water.
Competing Interests: Declaration of competing interest The authors declare that this study was conducted in the absence of any commercial or financial relationships that could be considered as a potential conflict of interest.
(Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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