The results of chlorine dioxide use after 23 years

Editor's note: This is the first of two articles that dig into Johns Hopkins Hospital's use of chlorine dioxide water treatment systems. The second article is scheduled to be published on May 19. 

Johns Hopkins Hospital's water treatment system helps to control Legionella presence in its potable water supply.

Image from Getty Images

Beginning in 2001, the Johns Hopkins Hospital in Baltimore installed chlorine dioxide (CIO2) water treatment systems in its inpatient buildings. The hospital evaluated the safety and efficacy of CIO2 for Legionella control throughout the potable water system. The evaluation included monitoring impact on Legionella, CIO2 residuals, disinfection byproducts, biofilm formation, corrosion, dialysis filtration systems, laboratory filtration systems and building water systems.

The application of the CIO2 system is designed and installed to optimize the efficacy of the disinfectant being used in the water treatment process. After 23 years of operation, an extensive Legionella analysis was performed. The data collected clearly indicates the successful control and elimination of Legionella in Hopkins’ water supply system. 

Hopkins installed CIO2 water treatment systems in four inpatient buildings as part of its Legionella prevention and control management plan. The hospital published a paper in October 2004 and presented the “Evaluation of Chlorine Dioxide in Potable Water Systems for Legionella Control in an Acute Care Hospital Environment” at the Engineers’ Society of Western Pennsylvania’s 65th Annual International Water Conference. The paper presented the hospital’s first application of CIO2_.

Data collected from 23 years of CIO2 water treatment to control and eliminate Legionella provides details on how Hopkins properly applies CIO2  treatment to potable water, the results of Legionella culturing, and equipment and system modifications that were made to prevent and control the growth of Legionella.

Disinfection selection

In 2000, the hospital researched available methods to disinfect municipal potable water as it enters the hospital’s potable water distribution system. The hospital required the disinfection method to meet standards from the Environmental Protection Agency (EPA) and the Maryland Department of the Environment (MDE) for potable water disinfection. The disinfection equipment meets NSF Standard/American National Standards Institute/National Standard of Canada 61: Drinking Water System Components – Health Effects, and the disinfectant meets NSF/ANSI/CAN 60: Drinking Water Treatment Chemicals – Health Effects.

Numerous disinfection methods were investigated, including sodium hypochlorite, monochloramine, CIO2, copper silver ionization and ultraviolet light. The investigation resulted with CIO2 being selected as the disinfectant process. CIO2 is approved by the EPA for use as a potable water disinfectant under 40 CFR Part 141 – National Primary Drinking Water Regulations. CIO2 also met the requirements of MDE and the hospital.

CIO2 is a gas that can be generated chemically or electrolytically from a sodium chlorite solution. Sodium chlorite is approved by the EPA as a precursor for generating CIO2 as a potable water disinfectant. CIO2 is a powerful oxidant and kills bacteria via oxidative disruption of cellular processes.

The CIO2 generator converts 25% sodium chlorite liquid into nearly pure CIO2 by utilization of an electrochemical oxidation process. The CIO2 equipment and associated delivery systems are operated and maintained by the hospital’s contracted water treatment company.

As a result of the hospital’s first trial application of CIO2 in 2001, CIO2 treatment systems were installed in three other hospital inpatient buildings.

Site and distribution

Hopkins receives potable water from the local city municipality, operated by Baltimore City Department of Public Works (BCDPW). BCDPW is responsible for compliance with the EPA drinking water regulations. BCDPW is required to ensure that the contaminants do not exceed the EPA’s Maximum Contaminant Levels (MCL’s) where applicable. Municipalities are not required to meet EPA Maximum Contaminant Level Goals. BCDPW utilizes chlorine (CI), an EPA-approved potable water disinfectant.

The hospital is connected to the city’s potable water system at two 100-pounds-per-square-inch gauge (psig) high-pressure potable water service and one 40-psig low-pressure potable water service. The 40-psig low-pressure potable water service is the backup in case of failure of the high-pressure water system. The hospital campus has inpatient buildings and numerous non-inpatient buildings varying in age. The inpatient buildings were constructed between 1974 and 2010. The inpatient buildings house medical-surgical patients, oncology patients, operating rooms, hemodialysis, sterile processing, pharmacies, laboratories, etc.

The hospital has a main potable water loop system that serves each building. The hospital had a 30-plus-years-old galvanized potable water main that serves each building. Due to the age and condition of the potable water main, it was replaced with stainless steel piping over a three-year period starting in 2019 and finishing in 2022.

Piping branches that extend off the potable water main to the buildings serve both the potable cold and hot water for each building piping distribution system. Each building has hot water converters which provide an average of 115 degrees Fahrenheit water to have 112 degrees Fahrenheit water at the distal outlets.

Potable cold and hot water piping systems in buildings are predominantly constructed of copper pipe. Potable cold and hot water is provided to sinks, lavatories, toilets, drinking fountains, water/ice dispenser, make-up water systems for equipment, etc.

Delivery system

In 2000, information was, and still is, minimal related to installing and operating CIO2 generators on a potable water system. There was also minimal information on CIO2 and its efficacy on Legionella. Therefore, it was necessary for the hospital to test and evaluate several engineering options with the goal of maximizing the effectiveness of the disinfectant.

Based on the design of each building’s potable water system capacity and projected water use, the CIO2 generators were installed at the starting point of each building’s potable water distribution system. Installation included CIO2 generators, CIO2 injection pumps, injection quills, flow meters, city potable water supply CI2 monitors, CIO2 monitors on the potable cold and hot water systems, pressure gauges, computer monitoring system, and associated electrical and piping connections.

Each CIO2 generator provides external safety alarms and multiple internal alarms. The external alarms include leak detection and to monitor when chemical levels and water flow are out of their safe ranges. These alarms are connected to the hospital’s building automation system (BAS). Additional safety alarms were added to monitor the CIO2 level, CIO2high limit, CIO2 low limit, loss of electrical power to chemical monitors and loss of electrical power to the CIO2 generator system.

Inpatient buildings A, B and C use CIO2 generators from Halox in each building; However, the system is no longer available on the market. Inpatient building D uses two CIO2 generators installed by PureLine based in Bensenville, Ill.

Chlorine, chlorine dioxide, chlorite monitoring

Performance testing and monitoring protocols were established early in the development of the treatment program. Testing is conducted daily for CI2, CIO2 and CIO2-negative residual levels per the Standard Methods for the Examination of Water and Wastewater, 20th Edition. Monthly operating reports for water treatment plants, which include CIO2 and CIO2-negative residual levels and total coliform are submitted to MDE monthly. Disinfectant byproduct self-monitoring reports for trihalomethanes and haloacetic acid and disinfectant residual monitoring reports for CIO2 and CIO2-negative are submitted to MDE quarterly. 

CI2 and CIO2 residual levels are monitored continuously via the BAS. CI2_, CIO2and CIO2-negative residual levels are obtained daily from both potable cold and hot water mains using EPA testing protocols. Chemical testing of the residual levels is to ensure that CIO2and CIO2-negative do not exceed the EPA’s Maximum Residual Disinfectant Level and MCL limits.

Monitoring and modifications

Corrosion monitoring. Extensive CIO2 corrosion testing was conducted as described in the 2004 paper “Evaluation of Chlorine Dioxide in Potable Water Systems for Legionella Control in an Acute Care Hospital Environment.” Monitoring of corrosion rates using corrosion coupons inserted into building potable water system indicate minimal impact on corrosion rates versus non-CIO2 treated potable water. Current testing identified no changes to corrosion rates due to the introduction of CIO2.

Dialysis and laboratory filtration equipment. Extensive CIO2 testing was conducted as described in the 2004 “Evaluation of Chlorine Dioxide in Potable Water Systems for Legionella Control in an Acute Care Hospital Environment” paper. The introduction of CIO2 and ClO2-negative continues not to create any adverse conditions with hemodialysis and laboratory filtration equipment.

Design/operational potable water system deficiencies and corrections. Design and operational deficiencies in several buildings were identified and corrected, including:

• Some existing potable cold and hot water piping was found to be oversized based on calculated maximum potable water usage. The actual potable water use was found to be significantly lower. Oversizing of piping resulted in low water velocities and laminar flow conditions. This environment promotes the growth of Legionella, bacteria and biofilm. Piping was replaced with properly sized pipes where feasible.
• Some booster pump oversizing based on calculated maximum potable water design usage was found. The actual potable water use was found to be significantly lower, resulting in the booster pumps being oversized. System over-pressurization, pressure surges and water hammer also were identified. These problems were corrected by adjusting pump operation, adjusting control valves and adjusting the system operating pressure where feasible.
• Some hot water piping systems that were based on calculated maximum water usage were determined to be oversized. The oversized hot water piping resulted in low water velocities and laminar flow conditions, reduced water circulation and poor temperature distribution. In some cases, piping was undersized, resulting in excessive velocities. Hot water piping systems were modified, and in some cases hot water return pumps were added, resulting in improved hot water circulation and temperature distribution.
• Hot water converter divertor valves were found to be undersized, and water service piping was undersized from the divertor valve to the convertor. This caused low hot water return flow to the converter and fluctuating hot water supply temperatures. Properly sized divertor valves were installed with full-size piping to the convertor and to the hot water supply piping. This resulted in the appropriate hot water return flow to the converters and stabilized the hot water temperature.
• Converter divertor valve thermostatic elements valves were found to be incorrect. Thermostatic elements were 110 degrees Fahrenheit. Divertor valve thermostatic elements valves start diverting hot water at 100 degrees Fahrenheit, bypassing the converter. At 110 degrees Fahrenheit, the divertor valve diverts all the return hot water, bypassing the converter. This was due to mixing of lower return hot water temperature with the higher hot water temperature from the convertor, which fluctuated the hot water supply temperature. This was resolved by installing 120-degree Fahrenheit thermostatic elements in the divertor valve that starts to divert water flow pass the converter at 110 degrees Fahrenheit. This eliminated the mixing of lower return hot water temperature with the higher hot water temperature from the convertor, resulting in stabilizing the hot water supply temperature.
• Manual faucets and electronic faucets were evaluated for Legionella and bacterial growth. Electronic faucets were found to grow Legionella and bacteria more quickly and at higher colony forming units (CFU’s) when compared to manual faucets. Testing was conducted on the electronic faucet internal components, such as the cold and hot water check valves, inline filters, solenoid valve and aerators. Testing also was conducted on manual faucets, which have cold and hot water cartridges and laminar flow control devices which are used instead of aerators. The lower Legionella and bacterial growth and CFU’s were the determining factors for the selection of manual faucets instead of electronic faucets on inpatient sinks.
• Laminar flow control devices are utilized instead of aerators on sinks for Legionella control. The laminar flow control devices eliminate aerosolization of the water and possible Legionella exposure while maintaining water flow control.
• The incoming city potable water occasionally contains debris, which could harbor Legionella and enter the hospital. To capture some of the debris, a potable water filter unit was installed at each inpatient building to remove incoming debris greater than 20 microns in size. These water filters have automatic back flush for draining to keep the filter mesh clean.

Check back next week for Part 2 of this article to learn about the results of Hopkins’ use of CIO2 to prevent Legionella growth in its potable water supply. 

Gregory Bova, M.D., Johns Hopkins Medicine, Baltimore.