Office building manages Legionella risk with point-of-entry filtration
Waterline Technology was asked to provide a recommendation to further reduce risk of Legionella for a premise plumbing potable water system in a 21-story office building. After a site visit and review of the management team’s goals, Waterline recommended filtering all potable source water for the building’s water heaters at the point of entry (POE) to reduce particulates and microbial contaminants, and provide filtered water for the hot water system and cooling tower makeup water. As a result of treating the source water that feeds the water heater, the cooling tower makeup water was automatically added as part of this treatment proposal.
The source water treatment system includes two 100-gpm stainless steel filter vessels: one for particulate reduction and one for microbial retention.
Several state regulatory agencies define chemical treatment of premise plumbing as secondary disinfection, and it is therefore subject to classification as a public water system as defined in the Safe Drinking Water Act.
Additional costs of regulation can include a certified plant operator, testing and monitoring equipment, and reporting as required by the state, which can easily add $10,000 to $15,000 per year to the operating cost of a chemical system. Any state may elect to exercise oversight of potable water premise systems that add chemical treatment within their facility.
The approach taken in this case study is considered a filtration process and is not viewed as secondary disinfection. Therefore, it is not regulated in that manner.
The potable water plumbing was not chemically or thermally sanitized after the new equipment was installed. The facility was unable to locate a company willing to tackle a building of this size to chemically or thermally shock a potable water system after filtration installation. As a result, the system may still contain biofilm or other substances that explain continual detection of Legionella at some distal sites. It is important to review the treatment after the hot water systems, which have excellent Legionella control.
As of Jan. 15, 2018, the additional filtration treatment system has been installed for four months, and the goal of a cartridge life of more than six months is on track. No significant differentiated pressure increases or flow rate decreases have been reported.
The hot water loop contains charged membrane filtration cartridges for microbial retention.
Issues & Benefits
This 280,000-sq-ft office building is estimated to use 5.32 million gal of water per year. The particulate and charged membrane filtration microbial retention filtration cartridges each have an estimated life of six to 12 months. The source water for hot water and cooling tower has a capital cost of $9,000. With an annual operating cost of $7,500, the cost per gallon is $0.003. The hot water has a capital cost of $3,000. With an annual operating cost of $3,750, the cost per gallon is $0.0023. The hot water is estimated to comprise 30% of the building’s total water usage.
While this article is intended to focus on the solution and not the cause of microbial issues, it is important to review the internal and external factors affecting every home and business regarding the health of their premise plumbing. For more information on conditions that promote bacterial growth, consult the Occupational Safety and Health Administration’s (OSHA) Technical Manual Section III.
While domestic cold water typically is not associated with Legionella growth, it has been detected in cold water in icemakers and dental lines. This sometimes can be contributed to water temperature in the lines exceeding 68°F due to ambient temperatures in the premise plumbing and stagnant water or low-use distal sites. One cannot rule out cross-connection as well, which can quickly contaminate downstream plumbing.
While many end users, such as hospitals, nursing homes and other high-risk population facilities install 0.2-µ point-of-use (POU) filters for showers and sink taps, the problem is not always eliminated. Because these filters have lives of 30 to 70 days, the operating cost can exceed $1,200 per distal site per year. Also, chemical systems such as chlorine dioxide, mono-chloramine, chlorine, ozone and copper silver ionization typically only treat the hot water and tend to have high operating costs. They require specialized treatment firms to maintain the system, as well as state approval of the installation.
Until the conditions in the incoming cold water supply described in the OSHA manual discussed earlier are reduced, the hot water premise plumbing will continue to be exposed to microbial and sediment issues. There is a seemingly constant barrage of public water boil order advisory notices that are never issued before the problem is present. Protection before, during and after these advisories is a crucial proactive approach many will need to implement to protect their potable premise plumbing.
Construction projects and infrastructure issues can cause disruption to source water. Dirt, sediment and scale can break off piping due to construction and break biofilm loose. Infrastructure issues can go undetected for long periods of time before boil order alerts are issued. Proactive treatment can reduce the risk of Legionella and other opportunistic organisms.
This non-electric, non-chemical POE solution, which is capable of greater than 6 log removal value (LRV) of Legionella and other opportunistic organisms, greater than 4 LRV of viruses and greater than 5 LRV of protozoans, coupled with POU treatment for distal sites that continue to test positive, can provide the risk reduction that the public water systems cannot supply. It will reduce risk of Legionnaires’ disease and other respiratory illness to employees and customers, and protect their brand and image in the market.