Replicable simulation of distal hot water premise plumbing using convectively-mixed pipe reactors

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 (P adonis = 0.001, R 2 = 0.222, P betadis = 0.785) and biofilm (P adonis = 0.001, R 2 = 0.119, P betadis = 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.

Influence of pipe materials on in-building disinfection of P. aeruginosa and A. baumannii in simulated hot water plumbing

“…CMPRs are an inexpensive, space-efficient, and replicable means of simulating distal, stagnant outlets off of risers from hot water recirculation lines ( Spencer et al., 2020 ). PVC, copper, and mild steel plumbing were simulated using sealed four-foot pipe segments composed of either ¾” PVC (Silver-line Plastics, Ashville, NC) (PVC CMPRs), half ¾” PVC and half type M copper pipe (McMaster-Carr, Elmhurst, IL) (copper-PVC CMPRs), or three-inches of ¾” mild steel pipe (McMaster-Carr, Elmhurst, IL) attached to forty-five-inches of ¾” PVC (iron-PVC CMPRs).…”

“…CMPR effluent was treated by adding 7.5% sodium hypochlorite bleach (Clorox, Alpharetta, GA) to 10% v/v before disposal. During this period, chemical and biological water quality was profiled to verify the replicability of CMPRs as reported elsewhere ( Spencer et al., 2020 ).…”

A Critical Review on the Factors that Influence Opportunistic Premise Plumbing Pathogens: From Building Entry to Fixtures in Residences

“…There have been several laboratory studies ,,− and a field-study aiming to understand how heater design and operation impact opportunistic pathogens. Most studies have found that water usage patterns and water heater design influence the chemical and microbial water quality. ,,, One study compared three configurations of residential electric water heating systemsstandard, recirculation, and tankless heatersin terms of volumes at risk for pathogen growth based on temperature measurements and water quality parameters while operating them at different use patterns.…”

Premise Plumbing Pipe Materials and In-Building Disinfectants Shape the Potential for Proliferation of Pathogens and Antibiotic Resistance Genes

“…The purpose of this study was to identify optimal combinations of in-building disinfectants and pipe materials that limit the proliferation of multiple OPPPs and ARGs in premise plumbing. We used convectively mixed pipe reactors (CMPRs), consisting of three pipe materials (PVC, copper, and iron), for replicated simulation of the distal reaches of premise plumbing and evaluation of the effects of chlorine, chloramine, chlorine dioxide, and copper–silver disinfectants. P. aeruginosa and A. baumannii were inoculated into the CMPRs as two representative OPPPs that are prominent agents of antibiotic-resistant , and nosocomial infections − that are also resistant to disinfectants. ,, After incrementally increasing disinfectant doses over a period of several weeks, disinfectants were removed to characterize the regrowth patterns.…”