For considerable years, Ultra Violet light has been popular as a method of sterilising mains water. Whilst it is recognised and documented that UV is effective in killing a range of micro-organisms, the concept of microbial treatment of water needs to be kept in the correct context.

When UV light was introduced as a method of treatment, the logic and science did appear sound. However, in the years since its introduction, significant research has been carried out and huge advances in our knowledge on waterborne pathogens has been made. To be succinct: If UV treatment performed as claimed, why is there thousands of installations of the equipment constantly reporting excessive microbial counts?

The reason for this is two key factors:

  • UV light is a focal (localised) method of disinfection and therefore offers no residual disinfection
  • UV light is used in the water treatment industry as a dechlorination process.

Both of these statements may not initially make a lot of sense regarding the topic, so let’s unravel the story.

The cause of microbiological contamination in water distribution systems is due to biofilm. Biofilm builds up on all surfaces that come in contact with water. This includes the walls of pipes. Biofilm is an organic secretion of certain bacteria, which they and other opportunistic organisms then use for shelter and protection.

Once colonies of bacteria have established in biofilm, it is very difficult to remove them.  As the biofilm grows, it bursts, and ejects planktonic (free floating) bacteria into the water.  These planktonic bacteria then move around in the water and attach to other surfaces and create further biofilm. Organisms then breed and the cycle continues ad infinitum.

Ultra violet light will agreeably destroy any planktonic organisms that are exposed to it, as the water flows past the light source. However the point being missed is that the UV light has no effect whatsoever downstream of the source. The issue in point is that there will always be biofilm present in any water distribution system, downstream of the UV light source.  Even brand new systems are infected before first use, by environmental exposure during construction, testing and commissioning.  Any organism that is released from the biofilm has the opportunity to either make it’s way to an outlet and infect a person, or, attach to the pipework further downstream and create another biofilm colony.

Even in the case of a recirculating ring main, or loop, with a UV light fitted in situ, the chances of an organism making it out of an outlet, or reattaching to the pipework are far greater than the possibility of it being brought back around to the UV light source to be destroyed.

The only way of preventing this scenario is to employ a residual disinfectant that continues it’s anti-microbial action long after it has been added to the water.

With regard to municipal mains water supplies, typically the only defence against planktonic (free-floating) micro-organisms in water is the chlorine added by the water authority.  Again, the chlorine is only effective against the free floating organisms, as it is not capable of penetrating the biofilm. However, at least it is active throughout the entire water distribution system, unlike the UV.

The significant point that we now arrive at is that Ultra Violet light is known to cause the destruction of chlorine. In other words, the process that has been employed against the planktonic organisms may very well be exacerbating the problem! Ultra violet light oxidises the free chlorine in water, basically removing it. Hence why swimming pools have the need to continually add chlorine to them, as the sunlight decomposes the chemical.

From this it becomes obvious that Ultra Violet disinfection no longer has a place in treating water passing through distributed systems. Unless long term residual biocides that are effective against organisms living in the biofilm are employed, success will never be realised.

Scientific studies clearly show that copper-silver ionisation is the logical method of disinfection that is effective against both planktonic and affixed organisms. Neither does it have the health risks and physical dangers associated with it that chemical disinfectants carry.

The Bion Systems AccuionTM technology is the clear worldwide leader in administering copper-silver ions into potable water. No other system has the ability to proportionally dose copper and silver into varying flow rates, whilst at the same time self-compensating for water chemistry and electrode wear.

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