Peace of Mind

Medium-pressure ultraviolet (UV) water disinfection systems from Aquionics’ British sister company are helping a number of bottled water producers in England keep their product free from microbial contamination.

Silver Spring

The first of these is the Silver Spring Mineral Water Co. in Kent, which supplies spring water and its own brand of soft drinks to the major British supermarkets.

“We have a very pure source of spring water,” said Steve Clegg of Silver Spring’s engineering team, “but we feel a take-no-chances approach to water purity is best, and medium-pressure UV provides us with that extra reassurance.” This was confirmed by Quality Assurance Manager Sue Hickling, who said, “UV gives us a high level of confidence to ensure consumer protection and satisfaction.”
Seven UV units are now installed at Silver Spring, the oldest of which has been in use for more than 10 years. “We use UV on all our bottling lines and also for our municipal water supply,” added Jason Crockford, company trainer.

Angel Springs

Another company benefiting from UV disinfection is Angel Springs, Ltd., situated in the picturesque Chiltern Hills outside London. The company, which bottles natural spring water for use in water coolers, recently replaced its ozone water disinfection unit with medium- pressure UV following concerns about disinfection byproducts being formed as a result of ozone treatment.

“We were put off by ozone because of the potential for bromate formation as part of the ozonation process,” said Angel Springs’ Andrew Glaister. Bromide ions occur naturally in many spring waters and are completely harmless. If their levels are high, however, ozone can facilitate their conversion into bromate, a suspected carcinogen.

“Even though our bromide ion levels are not particularly high, we decided to go for the safer option and use medium-pressure UV instead,” Glaister continued. “UV has no downsides, only upsides, and since its installation, we have been happy with its performance.”

Medium vs. Low Pressure

Medium-pressure UV is highly effective at destroying all water-borne microorganisms, including bacteria, yeasts, molds and their spores. It does not affect the pH or chemical composition of the water, ensuring flavor is not affected. Each UV system consists of a stainless steel treatment chamber containing one or more UV-emitting tubes surrounded by a protective quartz sleeve. Water passes through the chamber, and the UV kills any microorganisms present by destroying their DNA.

It has recently been discovered that some bacteria and other microorganisms contain enzymes that can repair UV-damaged DNA, a process known as “reactivation.” Some of these enzymes need visible light to perform the repairs (photoreactivation), while others can do so without light (dark repair). Photoreactivation is generally quicker than dark repair, but both of these phenomena pose obvious problems for operators of UV disinfection plants.

Recent research on the process, however, has produced interesting new developments. When comparing photoreactivation of E. coli DNA after exposure to UV wavelengths emitted by low- and medium-pressure lamps, independent research has shown that the DNA underwent extensive repair following exposure to UV from low-pressure UV lamps but virtually none following exposure to UV from medium-pressure lamps.

The researchers concluded that it was the broad UV output of medium-pressure lamps between 185 and 400 nm that has this desirable effect. By emitting UV over a wide range of the UV spectrum, medium-pressure lamps appear to damage other intracellular molecules, such as enzymes, in addition to DNA. It is this damage that seems to permanently inactivate the cells’ DNA repair mechanisms. Low-pressure UV lamps, on the other hand, produce only a single UV peak at 254 nm, which only affects DNA.

Permanent Microbial Deactivation

These preliminary results have serious consequences for operators of low-pressure UV disinfection systems. If, following exposure to low-pressure UV lamps, microorganisms are capable of recovering, operators need to seriously consider upgrading to medium-pressure technology. By providing permanent microbial deactivation, medium-pressure UV offers peace of mind, something low-pressure UV does not do.

Applications affected by these findings are wide-ranging and include municipal drinking water, bottled water, rinse or wash water in the food and beverage industries, swimming pools and aquaculture.


All Aquionics medium-pressure UV disinfection systems are easy to install with minimum disruption to the plant. They need very little maintenance; the only requirement is replacement of the UV lamps every 12 months, depending on use. This is a simple operation that takes only a few minutes and can be carried out by general maintenance staff. They also utilize automated wiping systems, which keep the quartz sleeves surrounding the UV lamps clean. The benefits of automated wiping are that no chemicals are needed for cleaning, and wiping takes place automatically during normal operation.

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About the author

Jon McClean is president of Aquionics. He can be reached at 859.341.0710, or by e-mail at [email protected].