© Fraunhofer IOSB-AST/Martin Käßler
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Germs on beer caps are now a thing of the past: Researchers at the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB Advanced System Technology Branch (Fraunhofer Institute IOSB-AST for short) in Ilmenau, Germany, have now developed a process that uses UVC LEDs – ultraviolet light-emitting diodes – in order to destroy bacteria. The nice thing about it is that the process is not only efficient but also environmentally friendly.

LEDs in comparison to mercury-vapor lamps

Until now, mercury-vapor lamps have been used for decontamination. But the harmful heavy metal has several serious disadvantages. For instance, if a lamp bulb breaks, the mercury is released into the environment. To prevent this, a mechanical device in the form of specialized lamp suspension, and shatter protection in the form of a protective tube are required. Which, by the way, do present their own set of problems. LEDs, on the other hand, are highly stable. They are thereby particularly suitable for use in mobile applications. For example, in vehicles, outdoors and in manufacture, where vibrations and shocks to machines are highly likely.

Moreover, mercury lamps require a special high-voltage ballast. LEDs, on the other hand, can be operated with low voltages. The former also need time to heat up after being switched on. LEDs do not, they reach their peak power immediately. LEDs are therefore able to sterilize things quickly, which is another advantage when it comes to their application. Mercury lamps also emit fixed amounts of mercury at a wavelength of 254 nm for physics-related reasons. This also has a disinfectant effect, but is much less efficient than what the new UVC LEDs are capable of.

“Conventional mercury-vapor lamps emit light at a wavelength of 254 nanometers and as such function below the optimum wavelength of 265 nanometers, this level of disinfection is not optimal,” explains Thomas Westerhoff, a scientist at the Fraunhofer IOSB-AST.

The mercury-vapor lamps also have a shorter service life. Owing to their bulky design they cannot be used flexibly, as mercury-vapor lamps are invariably elongated glass tubes. In contrast, LEDs are much smaller than their toxic competitors. They can thereby be arranged much closer together and in many different ways on an array for surfaces that are to undergo irradiation. In this way, a radiation beam’s geometrical shape can be specifically adapted to achieve a particular sterilization task.

The only disadvantage to LEDs which are used in the UVC range from 280 to 200 nm, is that they are not yet in mass production. As a result, they are relatively expensive. But that too could change soon. According to Westerhoff, OSRAM Optosemiconductor is currently setting up a production line in Regensburg for UVC LEDs, which is scheduled to go into operation in the second half of this year. This should lead to improved availability and a drastic drop in prices.

Germ-free in the beverage industry

The scientists of the “Applied System Technology AST” department, together with their project partner PURION GmbH (a manufacturer of UV disinfection systems for water treatment), now want to replace harmful, mercury-containing lamps with non-toxic, ultraviolet light emitting diodes.

Mark Wipprich, Purion CEO GmbH (left) & Dipl.-Ing. Thomas Westerhoff, Fraunhofer IOSB-AST (right) © Fraunhofer IOSB-AST/Martin Käßler

Incidentally, this new technology is not only suitable for disinfecting caps, but also for brewing water, among other things. In order to guarantee clean water for high-quality beer, UV systems are often installed upstream in brewing plants. When the brewing water passes through stainless steel pipes with integrated UV lamps, it is disinfected at the same time as well. This way the drinking water is able to be kept sterile. In particular, UV light in the wavelength range of 265 nanometers- the same wavelength provided by the new lamps – is perfect for killing bacteria, viruses and germs. This is because irradiation destroys the genetic material.

” This is why we prefer UV LEDs which emit a maximum of 265 nanometers. These UVC LEDs are especially interesting because their radiation destroys the pathogen’s DNA much more effectively. The UV rays generate resonances in the nucleic acids of the DNA and break the binding of the molecules. The nucleus of the microorganisms is altered in such a way that cell division becomes impossible. Consequently, the pathogens are no longer able to multiply,” Westerhoff explains.

Another bonus: LEDs are spotlights. Due to their radiation characteristics, they offer a broad spectrum of design options. Of course, the new technology can also be used to disinfect drinking water dispensers, beer kegs, bottles and cans as well as seals for beverages other than beer.

Field tests with high levels of performance

Westerhoff and his team at Fraunhofer IOSB-AST are responsible for the design of the LED modules and address issues such as “How should the dimensions be configured?”, “What does the optimal array design look like according to each specific application?”, “How many LEDs are required?”, “How are spotlights with varying wavelengths able to be mounted on the module?”

After conducting numerous practical tests, the researchers are able to operate the UV LEDs directly in water without the need for a complex protective tube. They were thus able to further increase the energy output of the radiation sources by eliminating reflections. The experts from Fraunhofer IOSB-AST have developed a special module for their industry partner PURION GmbH. Hereby the inner surfaces of the beer caps can be disinfected in the production process prior to filling the beer bottles. This ensures that no germs get into the bottles during the production process.

“We are able to irradiate of beer caps on the inside with a UV output of four watts. This is barely possible with mercury lamps on such a small area,” says the engineer.

Research into medical applications

The new technology is versatile. That is why the scientists at Fraunhofer IOSB-AST are also offering their expertise to the medical technology sector. Examples of applications include the design of LED-based UVC radiation sources and the simulation and optimization of irradiation fields. Thanks to their compact size and high radiation intensity, UVC LEDs are ideal for use in medical devices. Here they are able to disinfect liquids, surfaces and hard-to-reach areas in a targeted manner. Endoscopes and ultrasonic probes, for example, can be efficiently disinfected despite their complex irradiation shapes by using a clever configuration.

Nevertheless, since UVC radiation at a wavelength of 265 nm is extremely damaging to DNA – it inevitably leads to damage to the cornea of the eye – it is crucial to ensure that no one has eye contact with the LED. This means that visual protection is absolutely indispensable!

“We are already working on solutions which use UVC LEDs for the disinfection of instruments, surfaces and rooms in hospitals,” explains Westerhoff. And he reveals even more: “Together with PURION, we are currently working on a project for air disinfection (UVC) and air purification (UVA+TiO2) in refrigeration and air-conditioning units. But there is no prototype as yet”.

As a matter of fact, this technology is being promoted by the Federal Ministry of Education and Research (BMBF) as part of the ‘Advanced UV for Life’ 2020 initiative.