The legionella bacteria exists in both natural and purpose-built water systems, and in small amounts, it is relatively harmless, even if consumed in a glass of water.
Yet too many water systems, particularly those belonging to older buildings, offer an environment in which legionella can multiply. If the bacteria is inhaled in small droplets - cooling towers and showerheads are notorious sources of this type of airborne water - it can cause pneumonia-like lung problems.
This ‘legionnaire’s disease’ can be deadly, especially for the elderly and other persons with lowered resistance, such as transplant patients. Hotels and hospitals can see dozens of patients become infected in a short period.
Killing legionella with heat
Legionella grows best in tepid water, with its favourite environment around human body temperature, 37C (98.6F), although it can grow anywhere from 15C to 45C. Many building managers try to minimise the danger of legionella by heating all the building water to 65 or 80C to kill the bacteria.
This demands a great deal of energy and costs a great deal of money, but it works - at least at the source point where the water is hot. The problem is that water does not remain at this temperature throughout the water system. By the time it reaches a faucet, the ‘hot’ water has often cooled down and is in the zone where legionella can multiply. Meanwhile, ‘cold’ water can sometimes be brought into the legionella danger zone via close proximity with heated water in building columns.
Other building managers have invested in ultra-violet (UV) systems, which kill legionella at each water inlet. UV systems sound environmentally friendly, but they do little to eliminate the bacteria crawling in the invisible parts of the water system. These ‘gatekeeper’ UV systems also can’t reach the biofilm that grows on the inside of water pipes. That biofilm can provide an excellent breeding ground for legionella.
There is a more reliable way of eliminating legionella: introducing chlorine dioxide to the water, either at low levels on a long-term basis or at a high level in a ‘short, sharp, shock’ approach. This has the advantage of killing the legionella bacteria and removing biofilm throughout the entire system.
“In terms of effect, price and energy consumption, chlorine dioxide is simply the best choice,” says Morten Bang Jørgensen of Grundfos, which makes the Oxiperm Pro line of disinfection systems. “It costs less and works better than any other method against legionella.”
Still, Jørgensen says, some managers are reluctant to add chemicals to the water, fearing that the result might no longer meet the standards of potable water for their locality. (Oxiperm Pro can dose chlorine dioxide at levels that are well below those permitted in the U.K. and Europe). In fact, the majority of facility managers don’t confront legionella at all until there is an outbreak among peers in their region or industry. And if their peers are taking action, many managers may not know it.
“We’re always trying to highlight case stories among customers, but few ever want to admit to having done something to fight legionella,” Jørgensen says. “Partly, that’s because of liability concerns, but partly it’s because they don’t want to admit they ever had legionella in their systems. The truth is, though, almost all buildings do have some exposure to legionella. What’s important is that they take some action to keep the bacteria count from multiplying.”
Copy on this page is provided by Grundfos, sponsor of the water hub
More from the Grundfos partnerzone:
- Tackling the growing global problem of phosphate contamination in water
- Action on improving poor water quality needs to come from government
- Green and clean solutions to the dairy industry’s wastewater problems
