The hot legionella potato
High-temperature water control is used widely in potable hot-water storage and distribution systems in commercial and healthcare environments for legionella control. Despite this, the increasing complexity of system design and rising maintenance costs are prompting business leaders to consider more effective alternatives. Here Dr Simona Vasilescu, of the Water Treatment Platform at NCH, explains how oxidative technologies can be used to control the legionella hot potato.
Human beings are resilient creatures. This is certainly true when you consider the biology that makes up our internal structure. Stretching out all of our body's blood vessels would reach a staggering length of around 60,000 miles. It's incredible then, that our bodies are able to efficiently maintain a normal operating temperature of approximately 37 degrees.
However, despite the best efforts of engineers, it is still a challenge to create similarly efficient hot water storage and distribution networks, especially in commercial and healthcare environments where the risk of scalding is a bigger concern for young, elderly and disabled people as well as patients with sensory loss.
The long arm
The Government's Health and Safety Executive (HSE) regulates Legionella control with its L8 code of practice. This applies to water systems and includes the pipework, pumps, tanks, valves, showers, water softeners and calorifiers.
In commercial and business applications, the municipal water supply enters the building into a storage tank and is often pumped to a tank at the top of the building where, in static-occupancy environments, stagnant water and temperatures between 20 and 45 degrees Celsius can become a breeding ground for legionella bacteria.
Hot 'n' cold
Traditional temperature control includes the separation of water into dedicated hot and cold water systems. The cold water is stored at an ambient temperature below 20 degrees and the hot water is heated to around 60 degrees to kill any bacteria. Thermostatic mixing valves (TMVs) then mix the hot and cold water to provide a comfortable water temperature, which can then feed taps and showers.
Deadlegs and hard to reach areas of pipe work may not reach the 60 degrees required to kill legionella, increasing the presence of warm, stagnant water. Also, because the hot and cold water systems are often located in close proximity, such as in the central core or lift shaft of a building, heat exchange between the two pipes can raise the temperature of the cold water.
Even once a thorough risk assessment has been completed and your temperature controlled water system has been designed for safe and risk-free use, the ongoing maintenance, repair and energy bills will continue to rack up.
Because legionella regulations require water to be stored at 60 degrees, healthcare providers are some of the most energy intensive users of electricity in the UK. The NHS, for example, spends on average £750m annually, spread over 2,300 hospitals and 10,500 general practices as well as numerous additional trusts. The NHS carbon footprint equates to over 25m tonnes per year and is expected to rise given that energy costs are set to rise faster than inflation.
The alternative to high-temperature water control of legionella is to use chemical water treatment. The benefit of using biocides is that unlike heated water, which is prone to temperature dissipation in low flow areas, biocide dosage is proportional to the volume of water used and will remain in the system regardless of water flow.
Biocides can also be used to treat organic contaminants that enter the building through the mains water supply, another bugbear of building managers. Contaminants such as humus, the organic matter from soil, introduced into a system from the municipal supply, can assist in the build-up of bacterial slimes, providing the potentially hazardous legionella bacteria with an environment in which it can thrive.
Sodium hypochlorite, more commonly known as "Chlorine" has been traditionally used to treat water for the removal of bacteria and legionella. However, using Chlorine has some minor drawbacks in that it is slightly corrosive and can taint the taste of water.
There are other, non-chemical, water treatment solutions such as Ultraviolet (UV) light, which can kill bacteria in flowing water. However, UV light is not applicable to all applications because it has a reduced efficacy in areas of low or no-flow.
At Chem-Aqua we've developed a range of oxidative technology formats to choose from, including traditional liquids, solid pastes, tablets, powders and granules.
One of the most effective oxidative technologies is Chlorine Dioxide. Eight times more effective an oxidizing agent than chlorine, it achieves the same legionella killing and slime removal effect at a much lower concentration. An added benefit of Chlorine Dioxide is that it doesn't taint the taste of drinking water; one reason why, for example, supermarkets wash their fruits and vegetables in Chlorine Dioxide disinfected water.
Traditionally, one of the challenges of using Chlorine Dioxide has been the safety concerns involved in preparing a solution on-site using a Chlorine Dioxide generator. However, new forms of Chlorine Dioxide have been developed, including stabilized solutions and even solid tablets.
The fact remains that legionella bacteria continues to cause issues in water systems. HSE regulations have gone a long way in combating this problem, so much so that the UK is now leading the fight against legionella in Europe. Business leaders could make legionella treatment even more effective going forward, by considering a holistic process of chemical treatment and legionella testing to minimise colonised breakouts of legionella.