Pseudomonas

Pseudomonas, a microbiological organism found in water, can lead to problems in building water systems, be they drinking water, sealed heating or chilled water, or even in cooling tower systems.

Sealed heating and chilled water systems in buildings are another area where the bacteria may become a problem. Reduction in flow through pipework and warming of the system water may lead to slime formation. Reduction in flow through pipework and warming of the system water may lead to slime formation. This in turn may further reduce water flow and form sludges which block small bore pipe work and prevent the system working correctly. The slime may also harbour other undesirable bacteria, such as sulphate-reducing and nitrate-reducing bacteria, which can cause system corrosion, and reduction in the efficacy of water treatment chemicals. Chilled water systems are more likely to present these kinds of problems than heating systems, and new buildings may be particularly prone to bacterial growth if the system becomes fouled during construction.

Chilled water and heating systems can be protected from bacterial growth initially by correct flushing and treatment programs as soon as the pipe work is installed. The treatment should be ongoing, with regular maintenance checks of the treatment regime to ensure the correct amount of inhibitor is present and that there is no corrosion taking place. Regular dosing with a suitable biocide is advised. Once contaminated, thorough flushing and chemical treatment may be used with varying degrees of success to treat a sealed water system. The program will vary between systems, and can only be recommended after a site inspection and possibly the taking of pertinent water samples.

Pseudomonas bacteria in closed systems
It is not normal practice to include biocides into the feed water of Low, Medium, nor High Temperature (LTHW, MTHW, HTHW) Systems. Bacteriological problems, such as Pseudomonas are not normally encountered, where the water temperature at the boiler output is above 70C.

However in a construction project things are different, systems can lay dormant as parts of the project are finished, while others are still under construction.
Our comments concerning Pseudomonas can be summarised as follows:-

Pseudomonas in addition to other bacteriological strains are present in most water supplies,

The Pseudomonas organism present in public water supplies does not cause problems when in the planktonic (water borne) form, only when in the sessile form will 'bio-films' (slime) occur on heating and cooling system surfaces, with the resultant loss of efficiency and blockages of waterways;

The number of waterborne (planktonic) bacteria does not relate directly to the formation of Biofilm (slime) on surfaces. Their numbers indicate the potential for slime formation, given the right circumstances. When the circumstances are right, free floating (planktonic) bacteria become adherent and stick to solid surfaces such as a pipe-wall or tank wall, 'bio-films' are formed, (sessile bacterial populations);

Some Biocides which are effective against free living (planktonic) bacteria, are not at all effective on fixed (sessile) bacteria, as found in 'bio-films';

'Bio-films' can cover large areas of the internal surfaces of a water system; this is problem atical from the point of view of corrosion. When present in water systems 'bio-films' help in the formation of corrosion cells, there are several mechanisms at work;

'Differential aeration cells' whereby an area of metal surface becomes blinded with 'bio-film' and hence differences in oxygen concentration develop, leading to corrosion, differential aeration cells are the most common cause of corrosion.

Under the 'bio-film' the colonies of bacteria will be egesting waste material generated in the course of their normal lifestyle, some of these materials are corrosive.
Systems cannot be maintained in a completely sterile condition, especially when left full of water for extended periods of time, when they will inevitably stagnate.

Problems have not been encountered with any Bacteriological problems in systems where the companies Pre - Commission Cleaning has been carried out to BSRIA

Guidance Note AG2001/1, providing these systems are picked up as part of a proper preventative maintenance programme, whereby the system water quality is maintained to meet the requirements of British Standard BS2468 (1997). The reasons for this success would appear to be:

- Systems are properly chemically cleaned (to bare metal) and flushed;
- During the initial flush a biocide has been included;
- The final water treatment programme always includes an effective biocide.

Recommendations
To achieve control of biofilms in heating and cooling systems, including storage and pipe-work during the construction phase.

Other problematical bacterias within closed water systems:

Sulphate Reducing Bacteria
These bacteria are capable of breaking down sulphate to sulphide with the resulting problems of formation of hydrogen sulphide. Hydrogen sulphide is a toxic gas in large quantities and will also contribute to corrosion of pipework in a closed system.

Nitrate & Nitrate Reducing Bacteria
Organisms in this group are capable of using nitrate and nitrite containing compounds as an energy source, which in turn produces nitrogen gas. Again the action of these organisms can cause problems such as corrosion in a closed industrial system.

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