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Redefining solids filtration in process water

Engineers, manufacturers, utilities, public and private enterprise, commerce – in fact, anyone that uses water for temperature control – are, for the most part, quite comfortable in the belief that they are operating an effective and safe water system. But how safe are they really?

Standard guidance is that a chemical treatment regime must be put in place with adequate monitoring, and that this programme must provide the control of four key elements – scale, corrosion, micro-fouling and suspended solids – that can affect any cooling water system.

Generally, water treatment chemicals used together with pre-treatment plants will adequately control the potentials for scale, corrosion and biological fouling.

But what about suspended solids control? Because of the air scrubbing effect of cooling towers, for example, the potential for suspended solids to increase is always present.

Suspended solids contamination can come from many sources, such as wind-blown dust and seeds, pipework corrosion, system contamination from process, changes in raw water make-up or other local issues.

Of equal importance is the potential for airborne microbiological spores to be sucked into the cooling water.

A common practice to enhance the performance of the total water treatment programme is the inclusion of side-stream filtration.

Operational benefits of effective filtration in cooling water are very significant, not only contributing to good microbiological maintenance but also to maximise heat exchange efficiency and reduce maintenance costs.

Many industries feel safe having installed traditional technologies, which filter at best around 15-20micron. When we examine water samples from many systems, they typically show a solids loading from anywhere from 10mg/l to 80mg/l of physical matter – some even more where the make-up water is not mains water; for example, borehole water, river water or lagoon.

The issue is that when cooling water is sampled with an accurate laser analyser, it shows the efficiency level of filtration is high when it comes to the large solids while ignoring a situation that allows for the constant build up of fine particles or biofilms.

These biofilms provide an enhanced environment for further colonisation as well as acting as a filter for inorganic salts to build up. While many of these biofilms are invisible to the naked eye, they can increase the corrosion potentials at the metal surface and provide areas for rapid bacterial growth.

Biofilms will ultimately provide an environment where water treatment chemicals cannot function and can enable huge numbers of different bacteria to proliferate.

In conclusion, by not properly understanding, treating and filtering out the finer particles found in process water, the effect on cooling systems is minimal and biofouling is still an issue.

By installing a correctly sized side-stream, high-efficiency filter the return on investment for any user will be significant.

Steve Cupples is managing director of Industrial Purification Systems; John A Lewis is microbiologist for and group director of Waterman Environmental Group; Chris Mutch is managing director of M & S Water

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