Copper-silver ionization at a US hospital: Interaction of treated drinking water with plumbing materials, aesthetics and other considerations

Natural Organic Matter, Orthophosphate, pH, and Growth Phase Can Limit Copper Antimicrobial Efficacy for Legionella in Drinking Water

Copper (Cu) is a promising antimicrobial for premise plumbing, where ions can be dosed directly via copper silver ionization or released naturally via corrosion of Cu pipes, but Cu sometimes inhibits and other times stimulates Legionella growth. Our overarching hypothesis was that water chemistry and growth phase control the net effect of Cu on Legionella. The combined effects of pH, phosphate concentration, and natural organic matter (NOM) were comprehensively examined over a range of conditions relevant to drinking water in bench-scale pure culture experiments, illuminating the effects of Cu speciation and precipitation. It was found that cupric ions (Cu²⁺) were drastically reduced at pH > 7.0 or in the presence of ligand-forming phosphates or NOM. Further, exponential phase L. pneumophila were 2.5× more susceptible to Cu toxicity relative to early stationary phase cultures. While Cu²⁺ ion was the most effective biocidal form of Cu, other inorganic ligands also had some biocidal impacts. A comparison of 33 large drinking water utilities' field-data from 1990 and 2018 showed that Cu²⁺ levels likely decreased more dramatically (>10×) than did the total or soluble Cu (2×) over recent decades. The overall findings aid in improving the efficacy of Cu as an actively dosed or passively released antimicrobial against L. pneumophila.

A comprehensive evaluation of monochloramine disinfection on water quality, Legionella and other important microorganisms in a hospital

Opportunistic pathogens such as Legionella are of significant public health concern in hospitals. Microbiological and water chemistry parameters in hot water throughout an Ohio hospital were monitored monthly before and after the installation of a monochloramine disinfection system over 16 months. Water samples from fifteen hot water sampling sites as well as the municipal water supply entering the hospital were analyzed using both culture and qPCR assays for specific microbial pathogens including Legionella, Pseudomonas spp., nontuberculous Mycobacteria [NTM], as well as for heterotrophic bacteria. Legionella culture assays decreased from 68% of all sites being positive prior to monochloramine addition to 6% positive after monochloramine addition, and these trends were parallel to qPCR results. Considering all samples, NTMs by culture were significantly reduced from 61% to 14% positivity (p<0.001) after monochloramine treatment. Mycobacterium genus-specific qPCR positivity was reduced from 92% to 65%, but the change was not significant. Heterotrophic bacteria (heterotrophic bacteria plate counts [HPCs]) exhibited large variability which skewed statistical results on a per room basis. However, when all samples were considered, a significant decrease in HPCs was observed after monochloramine addition. Lastly, Pseudomonas aeruginosa and Vermamoeba vermiformis demonstrated large and significant decrease of qPCR signals post-chloramination. General water chemistry parameters including monochloramine residual, nitrate, nitrite, pH, temperature, metals and total trihalomethanes (TTHMs) were also measured. Significant monochloramine residuals were consistently observed at all sampling sites with very little free ammonia present and no water quality indications of nitrification (e.g., pH decrease, elevated nitrite or nitrate). The addition of monochloramine had no obvious impact on metals (lead, copper and iron) and disinfection by-products.

Inactivation of RNA and DNA viruses in water by copper and silver ions and their synergistic effect

Cu and Ag have been used as bactericidal agents since ancient times, yet their antiviral capacity in water remains poorly understood. This study tested the effect of copper (Cu) and silver (Ag) on model RNA and DNA viruses MS2 and PhiX 174 in solution at pH 6-8. Cu caused MS2 inactivation with similar rates at pH 6 and 7 but was inert towards PhiX 174 regardless of pH. Ag inactivated both viruses, causing denaturation of MS2 and loss of capsid spikes in PhiX 174. Ag inactivation rates were pH dependent and increased with increasing pH. At pH 8, 6.5 logs of PhiX were inactivated after 3 h and 3 logs of MS2 after only 10 min. The combined use of Cu and Ag revealed synergy in disinfecting MS2 at pH ≥ 7. Although metal concentrations used were higher than the desired values for drinking water treatment, the results prove a promising potential of Cu and Ag combinations as efficient viricidal agents.

Interactive Effects of Copper Pipe, Stagnation, Corrosion Control, and Disinfectant Residual Influenced Reduction of Legionella pneumophila during Simulations of the Flint Water Crisis

Flint, MI experienced two outbreaks of Legionnaires' Disease (LD) during the summers of 2014 and 2015, coinciding with use of Flint River as a drinking water source without corrosion control. Using simulated distribution systems (SDSs) followed by stagnant simulated premise (i.e., building) plumbing reactors (SPPRs) containing cross-linked polyethylene (PEX) or copper pipe, we reproduced trends in water chemistry and Legionella proliferation observed in the field when Flint River versus Detroit water were used before, during, and after the outbreak. Specifically, due to high chlorine demand in the SDSs, SPPRs with treated Flint River water were chlorine deficient and had elevated L. pneumophila numbers in the PEX condition. SPPRs with Detroit water, which had lower chlorine demand and higher residual chlorine, lost all culturable L. pneumophila within two months. L. pneumophila also diminished more rapidly with time in Flint River SPPRs with copper pipe, presumably due to the bacteriostatic properties of elevated copper concentrations caused by lack of corrosion control and stagnation. This study confirms hypothesized mechanisms by which the switch in water chemistry, pipe materials, and different flow patterns in Flint premise plumbing may have contributed to observed LD outbreak patterns.

Impact of commonly used Ag-Cu ion doses on Desulfovibrio sp.: growth and microbiologically induced corrosion against stainless steel

Ag-Cu ions in cooling water may inhibit the activity of sulfate-reducing bacteria and therefore provide solutions to microbiologically induced corrosion (MIC) problems, mainly caused by Desulfovibrio sp. To investigate this, the MIC behavior of Desulfovibrio sp. on 316L stainless steel in terms of growth and extracellular polymeric substances (EPS) production was investigated in the presence of Ag-Cu ions. Laboratory-scale systems were set up with final concentrations of 0.13 ppm Ag and 0.3 ppm Cu ions, as they are the frequently used doses for cooling waters, and operated over 720 hours. The corrosion rate was evaluated by gravimetric assay, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. The growth of Desulfovibrio sp. was assessed by bacterial counting and EPS production. Ag-Cu ions in the biofilm were assessed by inductively coupled plasma - optical emission spectrometry (ICP-OES) and EDS-elemental mapping analyses. It was concluded that the ion concentrations used caused an increase in EPS production, especially of protein. The corrosion rate of the metal by Desulfovibrio sp. in the presence of ions was detected as being 29 times higher than that in the sterile medium with the ions after 720 hours. The results suggested that Desulfovibrio sp. exhibited more corrosive behavior in the presence of non-toxic concentrations of Ag-Cu ions.

Legionellosis and Recent Advances in Technologies for Legionella Control in Premise Plumbing Systems: A Review

This review discusses Legionella, among the most prolific and publicly well-known waterborne pathogens, and advances in potential treatment technologies. The number of cases associated with Legionella continues to rise, as does its public awareness. Currently, cases associated with premise plumbing account for the largest number of legionellosis cases in the United States. So, while it is important to understand Legionella as such, it is also important to investigate how to treat drinking water in premise plumbing for Legionella and other waterborne pathogens. While there are currently several methods recognized as potential means of inactivating waterborne pathogens, several shortcomings continue to plague its implementation. These methods are generally of two types. Firstly, there are chemical treatments such as chlorine, chlorine dioxide, monochloramine, ozone, and copper-silver ionization. Secondly, there are physical treatments such as thermal inactivation and media filtration. Their shortcomings range from being labor-intensive and costly to having negative health effects if not properly operated. Recently developed technologies including ultraviolet (UV) irradiation using light emitting diodes (LEDs) and innovative carbon nanotube (CNT) filters can better control waterborne pathogens by allowing for the simultaneous use of different treatment measures in plumbing systems.

Rationally designed tubular coaxial-electrode copper ionization cells (CECICs) harnessing non-uniform electric field for efficient water disinfection

Though well known for its anti-microbial property, copper is usually not considered for drinking water disinfection because of its health risk to human bodies under efficient biocidal concentration. Herein, we have rationally designed and constructed a tubular coaxial-electrode copper ionization cell (CECIC) that enables superior disinfection performance (~6-log removal of E. coli) with a very low effluent copper concentration (~200 μg/L). A non-uniform electric field with enhanced strength near the center electrode is generated in the chamber attributed to the coaxial center-outer electrode configuration. Exposure to the strong electric field subsequently increases the permeability of cell membrane, the excessive uptake of Cu ions into microbes, and thus the reinforced bacteria inactivation. The in-situ ionization results in a Cu ion concentration gradient with higher concentrations in the regions closer to the center. In addition, being driven by the electrophoresis and dielectrophoresis forces, the bacterial cells are transported to the vicinity of the center electrode, where both the electric field strength and Cu ion concentration are higher. These mechanisms in the CECIC synergistically result in the high inactivation efficiency with low Cu concentration in the effluent. The low-cost, high-efficiency, and disinfection-byproduct-free CECIC has shown significant potential in point-of-use applications.

Georgeite: A Rare Copper Mineral with Important Drinking Water Implications

Significant research has been conducted on copper corrosion and solubility in drinking water, including the establishment of the "cupric hydroxide model". The model describes the temporal aging and associated solubility changes of copper minerals beginning with the most soluble solid, cupric hydroxide. Although the model explains copper levels in field observations well, there are aspects of the model that are not well understood, including a lack of evidence of the presence of cupric hydroxide in drinking water distribution systems. This study aimed to understand the effect of water chemistry on the solubility and properties of newly precipitated cupric solids, including mineral identification. Bench-scale copper precipitation tests were performed in water under a matrix of pH and dissolved inorganic carbon conditions. Copper solids were analyzed using a combination of materials analysis tools including XRD, FT-IR, TGA, and inorganic carbon analyses. Copper solids were X-ray amorphous, isotropic, and were light blue to blue. Based on repeated analysis, georgeite (Cu₂(CO₃)(OH)₂·6H₂O) was conclusively identified as the solid at all test conditions. Georgeite is an extremely rare, amorphous malachite analog, and because of its rarity, very little has been reported on its presence in any environment.

Water for Agriculture: the Convergence of Sustainability and Safety

Agricultural water is a precious and limited resource. Increasingly more water types and sources are being explored for use in irrigation within the United States and across the globe. As outlined in this chapter, the Produce Safety Rule (PSR) in the Food Safety and Modernization Act (FSMA) provide irrigation water standards for application of water to fruits and vegetables consumed raw. These rules for production and use of water will continue to develop and be required as the world experiences aspects of a changing climate including flooding as well as drought conditions. Research continues to assess the use of agricultural water types. The increased use of reclaimed water in the United States as well as for selected irrigation water needs for specific crops may provide increased water availability. The use of surface water can be used in irrigation as well, but several studies have shown the presence of some enteric bacterial pathogens (enterohemorrhagic E. coli, Salmonella spp. and Listeria monocytogenes) in these waters that may contaminate fruits and vegetables. There have been outbreaks of foodborne illness in the U.S., South America, Europe, and Australia related to the use of contaminated water in fruit and vegetable irrigation or washing. Unreliable water supplies, more stringent microbial water standards, mitigation technologies and expanded uses of reclaimed waters have all increased interest in agricultural water.

Interactive Effects of Corrosion, Copper, and Chloramines on Legionella and Mycobacteria in Hot Water Plumbing

Complexities associated with drinking water plumbing systems can result in undesirable interactions among plumbing components that undermine engineering controls for opportunistic pathogens (OPs). In this study, we examine the effects of plumbing system materials and two commonly applied disinfectants, copper and chloramines, on water chemistry and the growth of Legionella and mycobacteria across a transect of bench- and pilot-scale hot water experiments carried out with the same municipal water supply. We discovered that copper released from corrosion of plumbing materials can initiate evolution of >1100 times more hydrogen (H₂) from water heater sacrificial anode rods than does presence of copper dosed as soluble cupric ions. H₂ is a favorable electron donor for autotrophs and causes fixation of organic carbon that could serve as a nutrient for OPs. Dosed cupric ions acted as a disinfectant in stratified stagnant pipes, inhibiting culturable Legionella and biofilm formation, but promoted Legionella growth in pipes subject to convective mixing. This difference was presumably due to continuous delivery of nutrients to biofilm on the pipes under convective mixing conditions. Chloramines eliminated culturable Legionella and prevented L. pneumophila from recolonizing biofilms, but M. avium gene numbers increased by 0.14-0.76 logs in the bulk water and were unaffected in the biofilm. This study provides practical confirmation of past discrepancies in the literature regarding the variable effects of copper on Legionella growth, and confirms prior reports of trade-offs between Legionella and mycobacteria if chloramines are applied as secondary disinfectant residual.