In the U.S. alone, cases of Legionnaires’ disease have increased four and a half times since 2000. More than 6,000 cases of Legionnaires’ disease were reported in 2015, but that number is considered to be incorrect by the CDC.

On June 2, 2017, the Centers for Medicare & Medicaid Services (CMS) issued a memorandum titled “Requirement to Reduce Legionella Risk in Healthcare Facility Water Systems to Prevent Cases and Outbreaks of Legionnaire’s Disease.” The CMS policy in its entirety can be found at www.cms.gov.

Below you find a list of seven common systems used in protection and mitigation for domestic water service.

Protection/Mitigation Systems:

• Copper-silver ionization
• Chlorine dioxide addition
• Hyper-chlorination addition
• Super heating operation
• Ultra violet light treatment
• Monochloramine addition
• Ozone injection

Copper-silver ionization

Copper-silver ionization uses positively charged ions and silver ions. The ions bond electrostatically with negative sites on bacterial cell walls (biofilm). The continued presence of EPA-approved levels of 1.3 ppm copper and 0.1 ppm silver ions in the water systems (hot and cold) work to destroy biofilms that can harbor Legionella and other bacteria. It can take 30 to 45 days for copper and silver ions to penetrate a biofilm. The system will continue to monitor and maintain the water service month after month, providing one of the most effective protection systems to date.

A report was produced by the University of Arizona’s Lee K. Landeen (Department of Microbiology and Immunology), Moysar T. Yahya (Department of Nutrition and Food Service), and Charles P. Gerba (Department of Microbiology and Immunology and Department of Nutrition and Food Service). The article is titled “Efficacy of Copper and Silver Ions and Reduced Levels of Free Chlorine in Inactivation of Legionella Pneumophila.” (Chlorine is referred to in water treatment as “free chlorine.”) It explains the use of chlorine and copper-silver ionization in the inactivation of biofilm, which can harbor Legionella among other bacteria. Biofilm inactivation applied copper-silver ionization proved slower than free chlorine when compared. However, when copper-silver ions were added to low levels of free chlorine, inactivation rates of bacterial indicator organisms were proven to be more effective than free chlorine alone.

Another report titled “Controlled Evaluation of Copper-Silver Ionization in Eradicating Legionella Pneumophila From a Hospital Water Distribution System,” written by Zeming Liu, Janet E. Stout, Lou Tedesco, Marcie Boldin, Charles Hwang, Warren F. Diven and Victor L. Yu, took this a step further. This report evaluates the efficacy of copper-silver ionization over a limited time period in two hospitals with an active Legionella outbreak. I recommend giving this paper a read at bit.do/LegionellaControlled.

The pros and cons of copper-silver ionization are as follows:

Pro: When maintained correctly, this system has proven over time to have controlled Legionnaires’ disease as well as other pathogens in cold, hot and hot water return piping systems. Federal EPA-approved.

Con: Protection comes at a price. The upfront cost and maintenance involved to repair or replace parts can be pricey. Regional or local EPAs may or may not approve it.

Chlorine Dioxide (CIO₂) addition

CIO₂ is a neutral chlorine compound, and is considered to be very different from basic chlorine, both in its chemical structure and in its behavior. It has a high-water solubility, especially in cold water. Chlorine dioxide does not break down in water; it remains a dissolved gas. Typically, this is being applied in smaller secondary distribution systems that have a low cold water temperature, and no galvanized piping in the line being treated.

The following pros and cons were pulled from a report titled “Evaluation of Chlorine Dioxide in Potable Water Systems for Legionella Control in an Acute Care Hospital Environment.”

Pro: EPA-approved biocide is not negatively impacted by pH, and is superior to chlorine when water is above pH 7. Bacteria does not grow resistant to it. It works in cold, hot and hot water return systems.

Con: The facility needs a licensed individual and a specific license to operate the system. The chemical becomes volatile if it’s not stored correctly. It is also considered toxic, so the EPA has set a maximum limit of 0.8 mg/L for drinking water. A prolonged time is necessary to demonstrate significant reductions Legionella. The residual concentration in hot water is low (<0.1 mg/L) when the chlorine dioxide is injected into the incoming cold water at a concentration of 0.5–0.8 mg/L. Reactions with organic material and corrosion scale in piping can cause rapid conversion of chlorine dioxide to its by-products, chlorite and chlorate, which may pose health risks for consumers. Corrosion of galvanized pipes can cause loss of chlorine dioxide by reaction with magnetite (Fe304). This may affect efficacy.

Hyperchlorination addition

Some recommend increasing chlorine concentrations in water to between 10 and 15 mg/L. At this stage, it is recommended not to drink the water or bathe in it, as it may cause skin irritation and/or rashes. After hyperchlorination, the water has to be flushed out and replaced with fresh water. Mitigating with more than 5mg/L of chlorine tends to acidify the water. Once water is acidic, the chlorine becomes more corrosive. So, unless it is under careful control, hyperchlorination can be quite damaging to a water system. This process should be completed on cold, hot and hot water return systems.

If you combine hyperchlorination with chemical flushing, the effects can be even more dramatic. Chemical flushing will expose metal surfaces and make them more likely to be damaged by chlorine. Add to this that the reacted chlorine becomes chloride. Chloride is an excellent conductor of an electric charge. All a system needs, is mixed metals (copper/lead/zinc/iron), which is typical in older buildings, and an electric cell can be created. This is known as “galvanic corrosion.” It acts like a battery rapidly degrading metal components, and is difficult to stop. It also impacts the quality of the drinking water in a building by releasing metals into the water supply.

Some water supplies are treated with monochloramine. Hyperchlorinating a system that has monochloramine from the city water supply will create disinfection by-products that have a poor smell and taste. The EPA recommends lower doses of chlorine to reach “breakpoint” chlorination as a way around this problem.

As a possible alternative to hyperchlorination, maintain the chlorine levels in the water supply at 0.5 to 2 mg/L, which will control most bacteria. At these levels, the water is still safe to drink and bathe in and does not affect your piping system.

The pros and cons of hyperchlorination are as follows:

Pro: Relatively easy to apply, will kill off Legionella and many other microorganisms quickly.

Con: Hyperchlorination was found to be the most unreliable and also the most expensive disinfection system. Due to inadequate penetration of the agent into biofilms in piping it has fallen into disfavor, persistence of Legionella organisms in hyperchlorinated systems, corrosion of the water distribution system leading to pinhole leaks over time, and the introduction of carcinogens into the drinking water, effects last for only a few weeks.

Super heating operation

Super heating is focused on hot water systems, and will raise the hot water temperature in the system to 160 F. It will be flushed out of distal sites for a minimum of 30 minutes.

The pros and cons of super heating are as follows:

Pro: It kills Legionella in a matter of minutes.

Con: The obvious scalding concerns. The other cons are that a tremendous amount of water is wasted, and it only addresses the hot water systems.

Ultraviolet light treatment

The Water Research Center (www.water-research.net) explains ultraviolet rays (UV) as “[having] three wavelength zones: UV-A, UV-B and UV-C. It is this last region, the short-wave UV-C, that has germicidal properties for disinfection. A low-pressure mercury arc lamp resembling a fluorescent lamp produces UV light in the range of 254 nanometers (nm). A nm is one-billionth of a meter. These lamps contain elemental mercury and an inert gas, such as argon, in a UV-transmitting tube usually made from quartz. Traditionally, most mercury arc UV lamps have been the so-called "low-pressure" type because they operate at a relatively low partial pressure of mercury, low overall vapor pressure (about 2 mbar), low external temperature (50 C-100 C) and low power. These lamps emit nearly monochromatic UV radiation at a wavelength of 254 nm, which is in the optimum range for UV energy absorption by nucleic acids (about 240-280 nm).” The pros and cons of UV light disinfection are as follows:

Pro: Does not add chemicals to water, affecting taste. No need to deal with chemicals. Does not react with other impurities in water.

Con: High energy use to generate light. Efficiency decreases with time as the lamp degrades. Quartz tube needs to be kept clean so light reaches water. Water needs to be clear, not turbid. It is only a single treatment at the lamp, there is no residual treatment downstream.

Monochloramine (NH2CI) addition

Monochloramine (chloramine) is an inorganic compound with the formula “NH2Cl.” It is an unstable colorless liquid at its melting point of −87 F, but it is usually handled as a dilute aqueous solution, in which it is sometimes used as a disinfectant. Chloramine's boiling point is 75 F. It is listed as a carcinogen and mutagen.

Monochloramine is commonly used in low concentrations as a secondary disinfectant in municipal water distribution systems as an alternative to chlorination. Chlorine (referred to in water treatment as “free chlorine”) is being displaced by chloramine — specifically monochloramine — which is much more stable and does not dissipate as rapidly as free chlorine. NH2Cl also has a much lower tendency than free chlorine to convert organic materials into chlorocarbons such as chloroform and carbon tetrachloride. Such compounds have been identified as carcinogens. In 1979, the EPA began regulating their levels in drinking water.

If a municipality converts from chlorine to monochloramine as the primary treatment method, the hospitals in that municipality become inadvertent beneficiaries if they have a water system colonized with Legionella.

Pro: Monochloramine provides a stable residual that penetrates biofilms and has a wider working pH range than copper-silver ionization and chlorine.

Con: Monochloramine can cause anemia in patients undergoing hemodialysis. The onsite generation of monochloramine can be complicated; injecting hypochlorous acid upstream and ammonia downstream in a flow-through pipe could result in concurrent presence of free chlorine, ammonia and mono-chloramine because of incomplete mixing of the reactants.

Ozone injection

Ozone is a colorless gas with an odor that has been compared to the smell of the air after a thunderstorm.

Ozone is considered more effective against bacteria and viruses than chlorination. The oxidizing properties of ozone are said to reduce concentrations of iron, sulfur and manganese, as well as reduce or eliminate odor and taste issues. Ozone oxidizes the three elements to form insoluble metal oxides removed by post-filtration. Other organic particles and chemicals will be removed through coagulation or chemical oxidation. Ozone will degrade in a matter of a few seconds to 30 minutes, depending on the pH level and water temperature.

UV ozonation is the most common, while large-scale systems use either corona discharge or other bulk ozone-producing methods. Raw water is passed through a Venturi tube, which creates a vacuum and will pull the ozone gas into the water, or the air is bubbled up through the water being treated. Since the ozone will react with metals to create insoluble metal oxides, post-filtration is required.

In closing, a study evaluated 79 research papers found copper-silver ionization to be the only Legionella control technology that has been validated through a proposed four-step modality evaluation.

Proper sample collection is important to obtain accurate results. Manufacturers that manufacture copper-silver ionization technology recommend a copper concentration of 0.4 to 0.8 ppm and a silver concentration of .04 to .06 ppm, which comply with EPA drinking water standards. (EPA-approved levels are 1.3 ppm copper and 0.1 ppm silver ions in water systems.)

As you can see, there are many options to consider when determining which one to use for your next project.

If you missed it, read Part 1: Legionella Prevention. Part three of this series will apply everything we have covered in the previous two articles and apply the systems based on a facility’s water quality and data collection for records.