Scientists at a German institute are investigating use of ultraviolet light-emitting diodes (UV LEDs) to destroy bacterial DNA.

Fraunhofer researchers looked at replacing conventional lamps containing mercury with ultraviolet light-emitting diodes. The technology is suitable for disinfecting brewing water, caps for bottled beer, soft drinks, and mineral water during the filling process.

UV light can inactivate germs in drinking water. The disinfection process relies on mercury-vapor lamps, which emit light in the UV spectrum but the heavy metal may affect human health and the environment.

To ensure clean water for beer, brewing companies install ultraviolet (UV) systems upstream of brewing equipment. The genetic material (DNA) of bacteria, viruses and germs is destroyed by UV rays.

The technology project involving researchers at the Advanced System Technology (AST) part of the Fraunhofer Institute for Optronics, System Technologies and Image Exploitation IOSB and Purion GmbH was supported by the German Federal Ministry of Education and Research.

UV-C LEDs to destroy pathogens
Brewing water is disinfected by being pumped through stainless steel tubes in which UV lamps have been fitted. UV light with a wavelength of 265 nanometers is suitable for the task. Currently, UV light has been generated using mercury-vapor lamps, which emit light at 254 nanometers. The lamps also have long warm-up phases, short service lives and cannot be used flexibly due to bulky design. UV LEDs emit at a maximum wavelength of 265 nanometers.

Thomas Westerhoff, a scientist at Fraunhofer IOSB-AST, said conventional mercury-vapor lamps performance lies below the wavelength of 265 nanometers so the disinfection performance is not optimal.

“Of particular interest are UV-C LEDs, because their radiation destroys the DNA of the pathogens much more effectively. The UV rays generate resonances in the nucleic acids of the DNA and break the bonds of the molecules open. This changes the cell nuclei of the microorganisms in a way that renders cell division impossible. Consequently, the pathogens can no longer multiply,” he said.

UV LEDs do not require any warm-up phase as they reach full power instantly, they offer high mechanical stability and can be operated at low voltage. Such technology is already available on the market.

Following practical tests, researchers are able to operate the UV LEDs directly in water without the need for a tube to encase them. This eliminates reflections to increase the performance yield of radiation sources.

Experts at Fraunhofer IOSB-AST have developed a module that can disinfect the insides of beer caps during the production process before bottles are filled with beer for Purion GmbH. This ensures no germs get into bottles during the production process.