Abstract
A lack of replicable test systems that realistically simulate hot water premise plumbing conditions at the laboratory-scale is an obstacle to identifying key factors that support growth of opportunistic pathogens (OPs) and opportunities to stem disease transmission. Here we developed the convectively-mixed pipe reactor (CMPR) as a simple reproducible system, consisting of off-the-shelf plumbing materials, that self-mixes through natural convective currents and enables testing of multiple, replicated, and realistic premise plumbing conditions in parallel. A 10-week validation study was conducted, comparing three pipe materials (PVC, PVC-copper, and PVC-iron; n = 18 each) to stagnant control pipes without convective mixing (n = 3 each). Replicate CMPRs were found to yield consistent water chemistry as a function of pipe material, with differences becoming less discernable by week 9. Temperature, an overarching factor known to control OP growth, was consistently maintained across all 54 CMPRs, with a coefficient of variation <2%. Dissolved oxygen (DO) remained lower in PVC-iron (1.96 ± 0.29 mg/L) than in PVC (5.71 ± 0.22 mg/L) or PVC-copper (5.90 ± 0.38 mg/L) CMPRs as expected due to corrosion. Further, DO in PVC-iron CMPRs was 33% of that observed in corresponding stagnant pipes (6.03 ± 0.33 mg/L), demonstrating the important role of internal convective mixing in stimulating corrosion and microbiological respiration. 16S rRNA gene amplicon sequencing indicated that both bulk water (Padonis = 0.001, R2 = 0.222, Pbetadis = 0.785) and biofilm (Padonis = 0.001, R2 = 0.119, Pbetadis = 0.827) microbial communities differed between CMPR versus stagnant pipes, consistent with creation of a distinct ecological niche. Overall, CMPRs can provide a more realistic simulation of certain aspects of premise plumbing than reactors commonly applied in prior research, at a fraction of the cost, space, and water demand of large pilot-scale rigs.
Highlights
Opportunistic pathogens (OPs), such as Legionella, non-tuberculous mycobacteria, and Pseudomonas aeruginosa, account for the primary source of tap-water associated disease in the U.S and much of the world [1, 2]
This study evaluates the overall reproducibility of physicochemical properties and microbial community compositions produced by convectively-mixed pipe reactor (CMPR) using three pipe materials (PVC, PVC-copper, and PVC-iron) as compared to the same configurations maintained under stagnant, constant temperature conditions
Little variability in physical and biological parameters were observed across replicate CMPRs beyond that which is inherent to new pipe materials, allowing for relatively homogenous testing conditions
Summary
Opportunistic pathogens (OPs), such as Legionella, non-tuberculous mycobacteria, and Pseudomonas aeruginosa, account for the primary source of tap-water associated disease in the U.S and much of the world [1, 2]. Because these organisms grow in the premise Simulation of premise plumbing using convectively-mixed pipe reactors data are within the manuscript and its Supporting Information files
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