Written by: Gunvinder Bhogal, EngineerLive
“Ultraviolet (UV) technology was originally used to ensure the adequate disinfection of municipal drinking water. Since its introduction over 40 years’ ago it is now applied globally for disinfection, of water in many different industries, including food and beverage industries, pharmaceutical manufacturing, aquaculture and shipping.
UV kills all known spoilage microorganisms, including bacteria, viruses, yeasts and moulds (and their spores). It is a low maintenance, environmentally friendly technology which 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 (known as UV-C) has a strong germicidal effect, with peak effectiveness at 265nm. At these wavelengths UV eliminates 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 and 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 water, sugar syrups, beverages and effluent.
There are no microorganisms known to be resistant to UV – this includes pathogenic bacteria such as Listeria, Legionella and Cryptosporidium (and its spores, which are resistant to chlorination). The UV dose necessary for deactivation varies from one species to another and is measured in millijoules per square centimetre (mJ/cm2). Values for specific microorganisms have been experimentally established and are used to determine the type and size of UV system required.
The dose received by an organism in a UV treatment system is dependent on four main factors:
1. The energy output of the UV source
2. The flow rate of the fluid through the treatment chamber
3. The transmission value (ability to transmit UV light) of the fluid being treated
4. The geometry of the treatment chamber
By optimising these criteria, a UV system can be tailored to effectively treat large or small flows, as well as viscous fluids or those containing dissolved solids and high levels of starch or sugar compounds.
There are two main types of UV technology based on the type of UV lamps used: low pressure and medium pressure. Low pressure lamps have a monochromatic UV output (limited to a single wavelength at 254nm), whereas medium pressure lamps have a polychromatic UV output (with an output between 185-400nm).
Benefits of UV disinfection
UV disinfection has many advantages over alternative methods. Unlike chemical treatment, UV does not introduce toxins or residues into process water and does not alter the chemical composition, taste, odour or pH of the fluid being disinfected.
UV treatment can be used for primary water disinfection or as a back-up for other water purification methods such as carbon filtration, reverse osmosis or pasteurisation. Since UV disinfection does not rely on a chemical residual, the location(s) of the units should be carefully considered for optimum performance.
Food, beverage and brewing industries
Disinfection of direct contact water: Although municipal water supplies are normally free from harmful or pathogenic microorganisms, this should not be assumed. In addition, water from private sources such as natural springs could also be contaminated. Any water used as an ingredient, or coming in direct contact with the product, can therefore be a source of contamination. UV disinfects this water without chemicals or pasteurisation. It also allows the re-use of process water, saving money and improving productivity without risking the quality of the product.
CIP (Clean-in-Place) 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 high energy density, MP lamps are less affected by any sudden changes in the temperature of the CIP water than a LP lamp.
Filter disinfection: Reverse osmosis (RO) and granular activated carbon (GAC) are 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.
Cooling media and chiller disinfection: Some meat and dairy products are subject to contamination after heat treatment or cooking. UV provides an excellent way to protect foods from contamination by contact-cooling fluids.
Sugar syrups: Sugar syrups can be a prime breeding ground for microorganisms. Although syrups with 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.
De-aerated liquor: De-aerated liquor is added as part of a high gravity brewing process, often in the packaging operation. This liquor is added directly to the beer so needs to be kept free from contamination by gram negative bacteria, which can cause off-flavours and acidity.
Yeast preparation: The problems associated with yeast preparation in breweries are well recognised and include hazes, altered fermentation and surface membranes on packaged beer. A single cell of Sacchoromyces (var. Turbidans) in 16 million cells of pitching yeast will cause detectable hazes. UV destroys all known yeasts and their spores.
Wastewater: As part of a multi-barrier process, including filtration, UV can destroy microorganisms in the effluent from food and beverage facilities prior to discharge. As UV reduces reliance on hazardous chemicals, it also ensures all discharges meet with local environmental regulations.
UV as an alternative to ozonation
Nongfu Spring Co. Ltd., one of China’s leading producers of bottled water and beverages, has recently opted to use UV for its production plants across China. This is a major milestone in the bottled water industry – particularly in China – because presently in that country virtually all bottled water is disinfected using ozone. And around the world ozone is still the disinfection method of choice for many producers.
The decision by Nongfu Spring to opt for UV was driven by a number of reasons, not least of which was concerns about ozonation by-products such as bromate. In fact, Hanovia has noticed that more and more bottled water and soft drinks producers are now looking for ozone alternatives, and enquiries about UV are on the increase.
Bromide ions occur naturally in many spring waters and on their own pose no problem. However, the presence of ozone can cause conversion of bromide into bromate, with the consequent potential for consumer health problems. The World Health Organization (WHO) lists bromate as a carcinogenic substance and recommends its maximum limit in mineral water be set at 0.01mg/l (10ppb). In July 2008 the Chinese General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ), recommended in a revised draft national standard for drinking water and mineral water that a maximum limit for bromate in bottled water be in line the WHO guidelines. This limit has now been in force since October 2009.
Disinfection: As in the food and beverage industries, UV is used to disinfect water used in the manufacturing process, whether it is for direct product make-up or for rinsing and washing process equipment.
TOC reduction: Short UV wavelengths (below 200nm) are highly effective at breaking down organic molecules present in water, especially low molecular weight contaminants. The process works in two ways: the first method is by direct photolysis, when energy from the UV actually breaks down chemical bonds within the organics; the second method is by the photolysis of water molecules, splitting them to create charged OH- radicals, which also attack the organics.
Dechlorination: To date, the two most commonly used methods of chlorine removal have been granular activated carbon (GAC) filters or the addition of neutralising chemicals such as sodium bisulphite and sodium metabisulphite. Both of these methods have their advantages, but they also have a number of significant drawbacks. GAC filters, because of their porous structure and nutrient-rich environment, can become a breeding ground for bacteria. Dechlorination chemicals such as sodium bisulphite, which are usually injected just in front of RO membranes, can also act as incubators for bacteria, causing biofouling of the membranes. In addition, these chemicals are hazardous to handle and there is a danger of over- or under-dosing due to human error.
UV is now becoming increasingly popular as an effective alternative method of dechlorination. It has none of the drawbacks of GAC or neutralising chemicals, while effectively reducing both free chlorine and combined chlorine compounds (chloramines) into easily removed by-products.
Increased water extraction and lowered water quality can result in increased outbreaks of viral and bacterial fish diseases in the aquaculture industry. Due to the intensive nature of fish farming, fish stock is also highly susceptible to infection from natural fish populations in the water feeding the farm. To break the infection cycle between fish farms and natural fish populations, a disinfection system is needed to treat water entering and circulating within fish farms.
UV is ideally suited for these applications as it uses no chemicals and does not create by-products which would harm the fish stock, or other aquatic life, on discharge. Unlike other treatment methods, UV avoids the expense of complex monitoring systems involved in adding and removing chemicals before the water reaches the fish. In addition, it does not alter the pH of the water. Indeed, UV is the most economical disinfection technique that can be used in fish aquaculture. Applications include treatment of water in hatcheries, shell-fish purging tanks and fry rearing tanks, and recirculation water in marine parks and aquaria.
Swimming pools and spas
UV is now a well-established method of swimming pool water treatment, from hydrotherapy spas to full-sized competition pools. This growth in popularity has been largely due to UV’s reliability and ease of use. Another major factor is the reduced reliance on traditional chemical treatments it affords, particularly chlorine. UV is also highly effective at destroying chlorine-resistant microorganisms like Cryptosporidium andGiardia.
Some of the more unpleasant by-products of chlorination are chloramines, formed when chlorine reacts with sweat or urine in pool water. Trichloramines in particular are powerful irritants which are responsible for eye and respiratory complaints and the unpleasant smells commonly associated with indoor public pools. They are also corrosive and in time can lead to damage to pool buildings and structures such as ventilation ducts.
Another major benefit of UV is that it significantly reduces the need for backwashing and dilution, saving hundreds of pounds a month for pool operators.
Link between chloramines and asthma
A recent study found an increased incidence of asthma in children who swam regularly in chlorinated pools. In some cases the damage was equivalent to that found in heavy smokers. Even people sitting at the sides of pools, such as lifeguards and instructors, were found to be at risk.
The symptoms are caused, the researchers believe, by chloramines – particularly trichloramines. The problem is potentially so serious that the study’s authors suggested pool operators should seriously consider alternatives to chlorine-based disinfection. They also recommended better ventilation to help remove chloramine-laden air from pool surroundings, improved hygiene practices by bathers themselves – such as showering before swimming – and the regular renewal of pool water.
While further research is needed, these findings add further credence to the importance of reducing chloramines as much as possible.
Other UV applications
Ship Ballast Water: All ocean-going vessels take on water to provide ballast and stability. It is usually taken on in coastal port areas and transported to the next port of call, where it may be discharged. The IMO (International Maritime Organisation) sets tough standards to treat all ballast water prior to discharge, and UV disinfection – in conjunction with filtration – is now one of the accepted methods of treatment.
Meeting the increasingly rigorous hygiene standards required in the production of food, beverages and pharmaceuticals, as well water quality concerns in the leisure, aquaculture, shipping and oil drilling industries, is a real challenge. If improvements need to be made to plant and equipment, they need to bring quick returns on the investment and measurable improvements in product quality.
For manufacturers seeking to improve the quality of the end product, UV is an economic, realistic option. It is an established method of disinfecting drinking water throughout the world, and is now finding applications in many other industries.
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 every 9 – 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.”
Source: Bhogal, Guvindar. “UV Disinfection Technology – the Applications Just Keep on Growing.” Engineer Live. N.p., n.d. Web. 15 Sept. 2016.