Into the ultraviolet
23 Nov 2005
As Howarth acknowledges, this is not a new technology. The ‘ultraviolet’ part of the electromagnetic spectrum that, in the form of strong sunlight, can purify by permanently inactivating bacteria, viruses, moulds and spores, was identified almost a century ago.
Radiation with a wavelength between 240 and 280nm — primarily in the UVC spectrum — does the damage by disrupting the DNA of the contaminant, and it is this energy that is harnessed commercially by companies such as Hanovia.
Nearly all the UV radiation we receive from the sun is UVA (in the 315 to 380nm wavelength) and, in moderation, is perfectly healthy. Recent research points to UVB radiation (280-315nm) as being the most likely cause of skin cancers like melanoma, while UVC (generally below 280nm in wavelength) has long been known to have a germicidal effect. What Hanovia UV disinfection systems do is to generate the same UVC germicidal rays as sunshine, but at a strength hundreds of times larger.
Hanovia was founded in 1924, originally as a UV lamp maker. This is a feature of the company that continues to this day, as Howarth explains. ‘One of the key values Hanovia has,’ he says, ‘is that we are the only UV system supplier that actually makes its own lamps. There is an enormous amount of knowledge, experience and know-how involved in their manufacture, which contributes to their reliability and longevity.’
UV lamps used in sterilisation systems are either ‘low’ or ‘medium’ pressure, the terminology referring to the pressure of the inert gas inside the quartz UV arc tube. Hanovia offers both low and medium pressure technology, depending on the application. And here the company’s in-depth knowledge of the capabilities of its lamps comes to the fore.
According to Howarth, low-pressure lamps (which generally run at around 80W) might not have the same effect on some pathogens as the higher power rated (kilowatt levels) medium pressure lamps. This is because the lower output from the low-pressure lamp may only damage the DNA of the pathogens, which can then recover after later exposure to light and UVA. ‘It is the level of power and density of radiation that is important in killing the pathogens,’ he says.
Emphasising the importance of a UV supplier having this appreciation of its customer’s application, he says: ‘It is easy for someone to take a UV lamp, put it in a tube, pass water through it and then tell you it’s sterilised. What’s not so easy is for someone to do that and guarantee that it works. For that, you have to understood much more about the physics and chemistry and biology involved.’
Hanovia UV systems are used for treating water for all bottling lines at Silver Spring in Folkestone.
Hanovia takes its understanding even further by using CFD modelling to predict both flow patterns and radiation patterns within the sterilisation chambers of its systems. ‘We do this,’ Howarth says, ‘so we can accurately predict how the systems will work. If you can’t do that, it’s impossible to size a system properly and be able to guarantee it.’
The company’s systems can be found across the process industries, but different industries often have different dose requirements depending on the contaminating microorganisms they want to remove. The pharmaceutical industry, for example, might require a dose of 32mJ/cm2 for process water, while the brewing industry would require 50-60mJ/cm2 to control wild yeast.
Each Hanovia system is equipped with UV monitors that provide continuous output measurements of each UV lamp in the treatment chamber. These monitors, which respond only to the bactericidal wavelengths unlike non-specific wide-band photocells, can be linked to a plant’s control system so that power consumption can be optimised. The monitoring system can also be designed to initiate local or remote alarms, switch to stand-by units, or shutdown the system if necessary.
Hanovia’s own Photon control system features full traceability and data logging for up to 12 months. It shows system status on a simple display screen and can download data via an RS232C interface.
Apart from some standard systems, most of Hanovia’s output is designed for purpose. Treatment chambers have capacities up to 1500m3/h flow rate for the Photon range, while the largest system it offers, the Crossflow, gives effective treatment of up to 6500m3/h. The Crossflow is mainly for municipal-scale drinking water disinfection and is increasingly popular in the US on account of its ability to remove cryptosporidium — an application of UV that has yet to be sanctioned by the UK water industry.
UV disinfection can, of course, be applied to many fluids other than water. In the food and drink industry, for example, Hanovia supplies its UVS sugar syrup system. Concentrated sugar syrups have a high osmotic pressure that prevents microorganisms growing and reproducing. However, these will survive in spore form and will grow once the syrup is diluted into the food product or beverage. Installing a high output single UV arc tube in-line before the dilution step can comfortably meet the manufacturing specifications, without recourse to additives and preservatives, or the expense of plate heat exchangers for pasteurisation.
Disinfection may be the most common application for UV, but Hanovia is also involved in developing the technology for other industrial uses. Just as UV damages DNA in living organisms, so it affects many other chemical bonds. These effects, known as photolysis, include the emission of high energy photons which break molecular bonds; the conversion of non-ionic organic molecules to charged species that can be removed by ion exchange; and the production of hydroxyl (-OH) radicals that can cause photochemical breakdown.
Some recent photolysis applications include removing chloramines from water sources such as swimming pools, reducing residual chlorine levels from earlier treatment processes, TOC reduction, and the production of ultra-pure water for the semiconductor industry.
In many applications, however, the real advantage of UV, says Howarth, is that it doesn’t involve chemicals, and it has much lower operating costs compared with other techniques.
As the new man at the helm, Howarth (previously business director at Malvern Instruments) is understandably enthusiastic about both the technology and the company.
‘Hanovia is poised for some significant growth,’ he says. ‘The UV business itself is one where there are more applications than you would know what to do with. The technology has been around for quite a while, but applications for it are still being discovered. The company has a very bright future, and the process industries are very important to that future.’
