Remediating Legionella

Remediating Legionella from potable and non-potable water is no easy matter and may require several attempts before the treatment is successful for achieving non-detectable results.  Unfortunately due to the nature of these systems and the bacteria, there are very few permanent solutions. The only permanent solutions for preventing the bacteria from amplifying in a potable water require the installation of expensive and maintenance intensive equipment for delivery of chlorine, chlorine dioxide or copper silver ion treatment.

The proper design, maintenance, and temperature of a potable water system is the first defense for preventing the amplification of Legionella. Maintaining hot water above 135 degrees Fahrenheit and cold water less than 68 degrees Fahrenheit and eliminating dead legs or low flow areas goes a long way for prevention.  However this is not always feasible. There are several procedures that can be taken for emergency remediation, or routine treatment of a potable water system.  However, it needs to be understood that these are temporary solutions since the bacteria will rebound within a few weeks.  These cleaning protocols are listed below:

1. Heat treatment of hot water tanks and the complete water system includes raising the temperature of the system to 157 degrees Fahrenheit. This temperature needs to be maintained in the tank for 3 hours. The hot water needs to be drawn through all the outlets at 157 degrees Fahrenheit starting with the outlets closest to the hot water tank.. Sequentially work away from the hot water tank drawing water at 157 degrees Fahrenheit to all the outlets at a trickle flow rate for 3 hours. After this is completed, flush the hot water from the system and return it to normal operating conditions. If the capacity of the system is too low for heat treatment, then chlorination should be used.
2. Chlorination is accomplished by draining the hot water tank and manually cleaning it of debris. Remove all deposits by scraping followed by wet vacuuming of the tank. Fill the tank with clean water and add chlorine until 50 ppm of free chlorine is obtained through all the outlets including deadlegs and low use points and risers. Soak at this level of free chlorine for 16 hours. Test to ensure that a minimum of 30 ppm free chlorine is obtained at all outlet points for the 16 hours. After this has been accomplished, flush the chlorinated water from the system and test to ensure that less than 2 ppm chlorine remains in the system.
   
   According to the International Plumbing Code, this chlorination needs to be conducted for all new systems. Chlorination needs to conducted following major alterations to an existing system, if a system tests positive for Legionella, or after major upsets, water main breaks or breakdowns in a municipal   treatment system, or after a municipal water main system has been flushed.

Several studies have indicated that routine testing of a potable water system will identify a potential risk.  These studies suggest that it is not the concentration of the Legionella that is the best determination of risk, but rather the overall percentage of positive outlets.  Therefore, the goal is to establish a history of non-detectable results over time.

Remediating cooling towers is successful as long as the treatment is conducted in conjunction with an ongoing maintenance program of the tower.  Currently, the cleaning protocols for cooling towers can be found in the American Society of Refrigeration, Air Conditioning and Heating Engineers (ASHRAE), the Wisconsin Emergency Protocol (later withdrawn by Wisconsin but the revised version can still be found in OSHA Legionella Technical Document), and UK Health and Safety Executive Directive for Water Treatment HS (G) 70.  These protocols emphasize the need for routine maintenance, inspection, manual cleaning of system components and water treatment by professionals. Minimizing microbial growth, scale, corrosion, and sediment accumulation in the cooling tower components is critical for preventing the amplification of Legionella.

One approach for cleaning is used by Mark Hodgson and Drew Carlson of Packer Environmental. It is a modification of the UK Water Treatment Method HS (G) 70 and includes the following:

1. Chlorinate to 5-10 ppm for 5 hours with biodispersant; test for chlorine residual every 30 minutes
2. Completely drain the system
3. Manually clean the sump, tower pack, distribution system and drift eliminators to remove all deposits. Multi-celled systems can be cleaned sequentially.
4. Refill the system.
5. Chlorinate to 5-10 ppm for 5 hours with biodispersant; test for chlorine residual every 30 minutes
6. Completely drain the system; refill
7. Re-sample for Legionella after 2 weeks.

For systems having existing online chlorination, this first response is used to reduce (not eliminate) a positive Legionella result:

1. Maintain 5-10 ppm chlorine for 24-48 hours using a biodispersant
2. Re-sample for Legionella after the chlorine level drops below 0.5 ppm
3. Re-sample again after 2 weeks

In both scenarios it is important to review your treatment program. There is a reason you got a positive Legionella result in the first place.

Chlorination is the most effective method for emergency cleaning but excessive chlorination will reduce the life of the system components.  Deposits and biofilm reduce the efficacy of chlorination.  Routine cleaning and chlorination will reduce the presence of Legionella but it is not permanent solution. The organisms will re-grow in a few weeks.

Unless you change your cooling tower maintenance and treatment program, Legionella will re-appear. An overall maintenance program should include routine shut down of the system to manually clean and flush the system components. Treatment should include the use of corrosion inhibitors, biodispersants (chemicals used to breakdown biofilm) and oxidizing and non-oxidizing biocides. Non-oxidizing biocide treatment will penetrate the biofilm accumulation on the tower components.  Since Legionella multiply in the protozoans within the biofilm, controlling the biofilm is critical to controlling Legionella.  The non-oxidizing biocides need to be rotated frequently to eliminate the development of resistant bacteria.

Improperly maintained hot tubs and whirlpool spas are increasing being associated with legionellosis.  The Association of Pool and Spa Professionals has comprehensive guidelines for maintenance that are available for purchase (www.apsp.org). Considerations for the proper maintenance of these features include the following: Single-use systems should be completely drained between use and stored dry. Non single-use systems should be treated daily and cleaned weekly.  These should be cleaned, treated and stored dry at the end of the season.  Water treatment and filtration is essential whether these systems use potable or salt water.  Heavy bather load will increase the need for cleaning, treatment, and filtration.  Other organisms that can cause disease in these systems include Mycobacterium avium, Pseudomonas aeruginosa, Staphylococcus aureus, Naegleria fowleri and organisms that are associated with fecal contamination caused by children in diapers.

In summary, all the remediation protocols mentioned here are for a short term, immediate response; they should not be considered as permanent solutions.  If you return to operating your potable and non-potable water systems as before, the problem will return.  Continuous, proper, routine maintenance and treatment is the only way to prevent the amplification of Legionella.

For More Information Call Today:
East Coast 1-800-220-3675 x2528
or write to:
EMSL Analytical, Inc.
200 Route 130 North
Cinnaminson, NJ 08077

Latest Article

An Overview of Legionella Analyses

By Diane Miskowski, MPH EMSL Analytical, Inc.

The first recognized outbreak of Legionnnaires' Disease occurred in the US at the American Legion Convention in Philadelphia during the summer of 1976. read more...

Additional Resources

For additional information please click the links below.

Legionnaires' Disease
Clinical Microbiology Reviews
Cooling Technology Institute
more resources...

Legionella images courtesy of CDC, Public Health Image Library (PHIL)