By Jon McClean

Abstract
Effective microbial disinfection in the bottled water and beverage industries is essential. Ultraviolet (UV)disinfection is gaining increasing acceptance as a versatile treatment method. UV destroys the DNA of microorganisms and medium pressure UV, in particular, is highly effective at permanently inactivating microorganisms. UV reduces the need for chemicals and can be used to disinfect incoming water, clean-in-place water, waste water, filter systems and the surfaces of packaging. Further, UV systems are easy to install and maintain.

Introduction
In an increasingly regulated and safety-conscious market, the bottled water and beverage industries must meet ever more stringent standards of quality. Microbial growth due to contaminated water supplies or sugar syrups and flavorings can cause discoloration, off flavors and shortened shelf-life and add to the risk of infection of consumers. The threat of contamination is further increased as manufacturers respond to consumer demand for a reduction in chemical additives. Effective microbial disinfection of the whole production process is therefore essential.

A non-chemical method of disinfection gaining increasing acceptance is UV disinfection. UV kills all known spoilage microorganisms, including bacteria, viruses, yeasts and molds (and their spores). It is a low maintenance, environmentally friendly technology that eliminates the need for chemical treatment while ensuring high levels of disinfection.

How UV disinfection works
UV is the part of the electromagnetic spectrum between visible light and X-rays. The specific portion of the UV spectrum between 185-400nm (also known as UV-C) has a strong germicidal effect, with peak effectiveness at 265nm. At these wavelengths UV kills microorganisms by penetrating their cell membranes and damaging the DNA, making them unable to reproduce and effectively killing them.

A typical UV disinfection system consists of a UV lamp housed in a protective quartz sleeve, which is mounted within a cylindrical stainless steel chamber. The liquid to be treated enters at one end and passes along the entire length of the chamber before exiting at the other end. Virtually any liquid can be effectively treated with UV, including fresh spring water, municipal water, filtered process water, viscous sugar syrups, beverages and effluent.

There are two main types of UV technology, based on the type of UV lamps used: low pressure (LP) and medium pressure (MP). LP lamps have a monochromatic UV output (limited to a single wavelength at 254nm), whereas MP lamps have a polychromatic UV output (with an output between 185-400nm).

Advantages of medium pressure UV
For several reasons, UV systems based on MP lamps are better suited to the bottled water and beverage industries. Firstly, if fluids containing high concentrations of suspended solids (such as some mineral waters) are being treated, deposits can build up on the quartz sleeves surrounding the UV lamps, reducing their efficiency. To overcome this problem, MP systems utilize a mechanical wiper that passes back and forth along the length of the quartz sleeve, keeping it clean. This is much more difficult with LP systems, as they normally contain more than one UV lamp so automatic wiping is not always possible.

In addition, recent research comparing reactivation of E.coli DNA after exposure to UV emitted by LP and MP lamps showed that the DNA underwent extensive repair following exposure to UV from LP UV lamps, but virtually none following exposure to UV from MP lamps1,2,3.

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

Benefits of UV disinfection
UV disinfection has many advantages over alternative methods. Unlike chemical biocides, UV does not introduce toxins or residues into water and does not alter the chemical composition, taste, odor or pH of the fluid being disinfected. This feature is especially important in the bottled water and beverage industries where the chemical dosing of incoming process water can cause off-flavors and alter the chemical properties of the final product.

UV treatment can be used for primary water disinfection or as a backup for other water purification methods such as carbon filtration, RO or pasteurization. As UV has no residual effect, the best position for a treatment system is immediately prior to the point of use (POU). This ensures incoming microbiological contaminants are destroyed and there is a minimal chance of post-treatment contamination.

UV applications in the beverage industry
Spring water and municipal supplies
Although incoming spring water and municipal supplies are normally free from harmful or pathogenic microorganisms, this should not be assumed. UV disinfects this water without chemicals or pasteurization. It also allows the re-use of process water, saving money and improving productivity without risking the quality of the product.

Sugar syrups
Sugar syrups used for flavoring can be a prime breeding ground for microorganisms. Although syrups with a very high sugar content do not support microbial growth, any dormant spores may become active after the syrup has been diluted. Treating the syrup and dilution water with UV prior to use will ensure any dormant microorganisms are deactivated.

Clean-in-Place (CIP) rinse water
It is essential that the CIP final rinse water used to flush out foreign matter and disinfecting solutions is microbiologically safe. Fully automated UV disinfection systems can be integrated with CIP rinse cycles to ensure final rinse water does not reintroduce microbiological contaminants. Because of their mechanical strength, MP lamps are not affected by any sudden changes in the temperature of the CIP water, such as when hot (80oC/176ºF) liquid is instantly followed by cold (10oC/50ºF).

Filter disinfection
Stored RO and granular activated carbon (GAC) filtrate is often used to filter process water, but can be a breeding ground for bacteria. UV is an effective way of disinfecting both stored RO and GAC filtered water and has been used in the process industries for many years.

Dechlorination
GAC filters are also often used to dechlorinate process water, removing the ‘off’ flavors often associated with chlorine disinfection, meaning the flavor of the final product remains untainted and free from unwanted flavors or odors. Placing UV systems ahead of GAC filters used for dechlorination improves the performance of the filters and results in longer carbon runs, thereby decreasing operating costs.

Packaging & surface disinfection
Surface disinfection systems are used to reduce microbial counts on all kinds of packaging, including glass and plastic bottles, cans, lids and foils. By irradiating the surfaces with UV prior to filling, food spoilage organisms are eliminated, extending the shelf life of the product and reducing the risk of contamination.

Tank head space disinfection
UV systems can be used to disinfect displacement air for pressuring tanks or pipelines holding perishable fluids. Storage tanks are particularly susceptible to bacterial colonization and contamination by air-borne spores. To prevent this, immersible UV treatment systems have been designed to fit in the tank head air space and disinfect the air present.

Waste water
Effluent from manufacturing facilities can be treated without the use of environmentally hazardous chemicals. This ensures all discharges meet with local environmental regulations. As already mentioned, because process water can be treated and re-used with UV, this also leads to a significant reduction in the amount of waste water produced.

Case studies
MP UV water disinfection systems from a British company are helping a number of bottled water producers in England keep their product fee from microbial contamination.

Angel Springs Limited, situated in the picturesque Chiltern Hills outside London, bottles natural spring water for use in water coolers. The company recently replaced its ozone water disinfection unit with MP UV following concerns about disinfection byproducts (DPBs) being formed as a result of ozone treatment.

“We were put off ozone by the potential for bromate formation as part of the ozonation process,” said Angel Spring’s 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. Since its installation, we have been extremely happy with its performance.”

Silver Spring Mineral Water Company in Kent, which supplies spring water and own-brand soft drinks to the major British supermarkets, is also benefiting from UV disinfection.

“We have a very pure source of spring water,” commented 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 over 10 years. “We use UV on all our bottling lines and also for our municipal water supply,” added Company Trainer Jason Crockford.

Conclusion
Meeting the increasingly rigorous hygiene standards required in the production of bottled water and beverage products is a real challenge. If improvements need to be made to plant and equipment, they need to bring quick returns on investment and measurable improvements in product quality.

For those manufacturers seeking to improve the quality of the end product, MP UV is an economic, realistic option. It is already a well-established method of disinfecting drinking water throughout the world, widely used for high purity applications such as pharmaceutical and semiconductor manufacturing, where water of the highest quality is required.

MP UV disinfection systems are easy to install, with minimum disruption to the plant. They need very little maintenance, the only requirement being replacement of the UV lamps once a year, depending on use. This is a simple operation that takes only a few minutes and can be carried out by general maintenance staff.

References

  1. Oguma, K., Katayama, H. & Ohgaki, S. (2002). Photoreactivation of Escherichia coli after low- or medium-pressure UV disinfection determined by an endonuclease sensitive site assay. Applied & Environmental Microbiology, Vol. 68, No. 12, 6029-6035.
  2. Zimmer, J. L. & Slawson, R. M. (2002). Potential repair of Escherichia coli DNA following exposure to UV radiation from both medium- and low-pressure UV sources used in drinking water treatment. Applied & Environmental Microbiology, Vol. 68, No. 7, 3293-3299.
  3. Zimmer, J. L., Slawson, R. M. and Huck, P. M. (2003) Inactivation and potential repair of Cryptosporidium parvum following low- and medium-pressure ultraviolet irradiation. Water Research, Vol. 37, 3517 – 3523.

About the author
With over 10 years UV experience, Jon McClean is President of Aquionics Inc. ,a market leader in UV technology for disinfection, deozonation, dechlorination and TOC removal. Aquionics is part of Halma Plc., with affiliates in the United Kingdom and Holland. McClean can be reached at (859) 341-0710, (859) 341-0350 (fax), email: jon.mcclean@aquionics.com or contact the company: Aquionics, Inc. 21 Kenton Lands Road, Erlanger, KY 41018, website: www.aquionics.com.

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