WATER TREATMENT, PUMPS & DRAINAGE


Secondary disinfection plays a critical role in water system maintenance


Once a water system is in good order, secondary disinfection provides long-lasting protection by significantly inhibiting the growth of microorganisms that cause harm to human health. Ian Wedd, from Guardian Water Treatment, explains the benefits of the ‘belt and braces’ approach for buildings that are used intermittently, such as schools


M


ost buildings go through periods of low occupancy at times, schools, however, are only ever in use at full capacity for 38 weeks of the year – and not always


at weekends. When educational facilities are used intermittently like this, water quality in HVAC and potable water systems can deteriorate posing a threat to returning occupants.


As the Christmas holidays come to an end and the children go back to the classroom, proper water treatment practices will ensure that systems are working efficiently, keeping winter fuel bills to a minimum, and, more importantly, that they are free harmful from bacteria, such as legionella. A robust water treatment strategy should include flushing alongside primary and, where necessary, secondary disinfection. There are several types of disinfectant to choose from; the development of new non-toxic disinfection techniques such as hypochlorous acid (HOCI) are improving safety for water treatment engineers, building occupants and the wider environment.


Legionella – don’t take the risk


Legionnaires’ disease is a severe form of pneumonia that causes inflammation of the small air sacs in the lungs and associated tissues. It is caused by people inhaling legionella bacterium, which proliferates in unused water systems and then becomes airborne once taps and other outlets are brought back into use. Generally, a few days without water movement is enough to increase the risk of legionella growth. Debris such as rust, sludge, scale and biofilm will also encourage bacterial proliferation. Flushing helps to improve water quality and reduce the risk of legionella by removing sediments and giving the system a thorough clean. There is no specific guidance as to frequency, but it is unlikely that manually running the taps to prevent stagnation from time to time would be enough to replicate full water usage – especially when a building has been empty for weeks.


Enhanced protection


Flushing and disinfection should not be the end of the line when buildings are used


intermittently. Once a system is clean, facilities and building managers should prioritise maintaining water quality and system condition to prevent bacterial re-growth during times of inactivity. Secondary disinfection provides robust mitigation against legionella, minimising the risk of future outbreaks and protecting valuable HVAC assets from degradation. It is recommended for a wide variety of sectors and buildings, not just those that are underused, and is something that all FMs should consider as part of their long-term water treatment strategy. As well as increasing safety for occupants, a well regimented programme of water disinfection that includes secondary disinfection methods can significantly help to ensure that responsible parties are compliant with relevant guidance and legislation, including the UK, Northern Ireland and Scotland Drinking Water Regulations, HSE’s ‘The control of legionella bacteria in water systems - Approved Code of Practice and guidance’ (ACoP L8) and WHO Guidelines for Drinking Water Quality.


Secondary disinfection methods


Traditionally, secondary disinfection was delivered using powerful chemicals, including bleaches, chlorine dioxides and monochloramines – extremely effective but potentially highly corrosive and dangerous. In recent years, more sustainable, cost-effective and non-toxic methods have been developed that do the job just as well. Whichever method is


chosen, water testing and monitoring throughout is key to achieving the desired results.


Chlorine dioxide (ClO2): A fast-acting biocide commonly used in potable-systems to control TVC levels, legionella and other harmful bacteria. Treated water used to flush the system provides a constant low-level defence that is far more effective than flushing alone. However, ClO2 is highly toxic to humans and animals, making it risky to handle, and its efficacy can be reduced subject to fluctuations in flow and if it is not stored correctly.


Hypochlorous acid (HOCI): An alternative and much safer approach to secondary disinfection is to use HOCl, a non-toxic biocide that has grown in popularity since the first COVID-19 lockdown in early 2020. Uses include wound care and hand sanitisation, but it has also been found to be highly effective in the water treatment sector, breaking down biofilm and killing pathogens and bacteria commonly found in water systems. In HSG 274 Legionella Technical Guidance, HOCl is described as “the form of chlorine that is most effective as a biocide”.


HOCl is particularly useful for systems with low and high pressure, high bacteria-counts, embedded or systematic biofilm challenges. It can be used as a permanent secondary disinfection for stubborn systems where repeated flushing and on-off dosing has been ineffective. Like ClO2, HOCl is extremely efficacious and fast-acting, however it is much safer for humans and requires no special handling or PPE. Its long shelf life contributes to reduced wastage and costs and it has a far lower carbon footprint than other solutions.


Ideal for small, medium and larger applications, HOCl is delivered in a variety of package sizes and can be dosed into incoming mains or a break tank, via fixed or mobile delivery and control systems, depending on system requirements.


Safer spaces for all


Whilst there are no panaceas, secondary disinfection plays a critical role in water system maintenance and can have a significant impact on microbial activity, providing a second-line of defence in buildings left vacant for any length of time. When buildings are opened back up, FMs can be safe in the knowledge that they’ve done everything they can to ensure water condition and system safety.


As part of our ongoing commitment to sustainable water treatment, we are championing HOCl as a secondary disinfection method; not only is it highly effective, but it is also chemical free, naturally occurring and non- toxic, leading to safer working environments for water treatment engineers and safer spaces for building occupants. Guardian Water Treatment is a leading water system management provider. For more information, visit www.gwtltd.com.


10 BUILDING SERVICES & ENVIRONMENTAL ENGINEER FEBRUARY 2023 Read the latest at: www.bsee.co.uk


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