Open-access content Monday 8th February 2016
11 February 2016 | By Steven Booth
Pseudomonas is a common bacteria that could be responsible for corrosion and inefficiencies in your building's water system. Steven Booth explains how FMs can prevent it.
Although certain types of Pseudomonas can be dangerous to humans, there are many species that are not a health risk and in closed circuit water systems, contact with the outside world is limited - it is the water system itself that is at risk from its effects.
SymptomsAny stagnant or low-flowing water will give Pseudomonas the perfect conditions to multiply, leading to biofilm formation and other problems such as corrosion and the rise of sulphate reducing bacteria (SRBs).
- SRBs: These metabolise naturally occurring sulphate in the water to produce sulphide under clumps of bacteria, depolarising the metal surface, resulting in localised pitting corrosion and eventual perforation.
- Biofilm: In general, bacterial build-up in the water, especially in stagnant areas, can create a microbial biofilm layer on pipe and heat exchanger surfaces, causing a reduction in efficiency and flow restrictions. Preventing biofilm from forming is essential; once biofilms start to form, the bacteria that reside within them can be thousands of times more resistant to biocides than that found free floating in the water.
Dead leg problemsA key exacerbator of Pseudomonas build-up in large commercial buildings is 'dead legs' (a redundant length of pipe work). The risk of bacterial growth in dead legs is well documented for heating and cold water systems, but the same problem also occurs in closed systems.
Often included to make way for future expansion, these potentially vast areas of stationary water present the ideal conditions for bacteria to grow. Dead legs can also be created if certain areas of the system are not circulated regularly.
Once bacteria have taken hold on a grand scale it can be difficult to get things back under control. Although removing 'dead legs' altogether may not be practical, we suggest that designers include a bypass or flow around the dead end to combat the problem and implement a valve-exercising regime to create full circulation.
To set the stage for continuing water hygiene, FMs need to be confident that the water system they're taking on has been built and prepared with bacteria prevention in mind.
Pre-commissioningPre-commissioning cleaning is a standard requirement of all new closed water installations, and is carried out under the latest BSRIA guidelines. Remediation cleaning of existing systems that have fallen out of control is possible, but it will never render a system quite as good 'as new'.
Before FMs are handed the care of a water system, the following pre-commissioning cleaning techniques should be employed.
- System dynamic flushing: System dynamic flushing removes debris from the system to reduce the potential for blockages by maximising flow rates through main risers and sub branches.
- Biocide wash: A full biocide wash to remove bio-films and bacteria from the system.
- Chemical cleaning: Following commissioning, movement of the pipe work, owing to thermal expansion or contraction, may cause contaminants such as iron oxide (rust) to be released into the fluid stream. Chemical cleaning loosens surface deposits so they can be removed from the system to create a stable surface within the pipe work. This, if maintained by an continuing water treatment regime, will inhibit further corrosion.
- System inhibiting: On completion of the chemical clean, the system is dosed with a suitable corrosion inhibitor and biocide to make sure of continuing protection from water, metal corrosion and biofouling.
- Back flushing: All terminal units should have been isolated during pre-flushing procedures. The purpose of back-flushing is to remove any small debris that has collected within these terminals.
Pseudomonas barrierOnce the area is cleaned, Pseudomonas can be stopped from entering the building by creating a preventative non-chemical barrier that water flows through. Photocatalytic water purifiers greatly reduce bacterial levels in the water. A specific frequency of light and photocatalytic surfaces are used to create free radicals that break down harmful microorganisms and other pollutants in water. The free radicals are short-lived and exist for
only milliseconds, which means they have no possibility of leaving the reaction chamber.
A photocatalytic water purifier such as Guardian's AOT Wallenius can produce a Log 5 reduction in Legionella and Pseudomonas bacteria levels within the water that passes through it, killing 99.9 per cent of microorganisms.
For FMs, this approach means a reduction in the need for chemical dosing, which reduces continuing maintenance requirements and the need to purchase biocides.
Water treatment should never be an afterthought. Cutting corners at the construction stage will leave those responsible for ongoing maintenance with a far harder task - bacteria may be prolific and more difficult to get under control, with increased man-hours and chemicals required to deal with its issues..
Steven Booth is associate director at Guardian Water Treatment