Ultraviolet LEDs
purify water
Most marine aquarists are familiar with UV-sterilizers that can be
used to free the aquarium water of
certain harmful micro-organisms.
This type of prophylactic sterilization is often recommended for the
first two weeks after the introduction of new coral fishes to a reef
tank, and the rearing of the larvae
of numerous coral-fish species is
quite simply unthinkable without this method of water treatment.
Various methods of producing germicidal ultraviolet radiation are
known, and now it seems another is to be added, with the possibility of
aquarium-hobby UV-sterilizers with a very much longer working life being
available in the future. A research group at the Ferdinand Brown Institute
and the Technical University of Berlin are working on methods of disinfecting water in a less complicated and more environmentally friendly way
than hitherto, using ultraviolet light-emitting diodes (UV LEDs). The Irradiation with UV light destroys the DNA of bacteria, viruses, and spores
and thereby prevents them from reproducing.
The UV light was produced using semiconductor-based InAlGaN light-emitting diodes. Using an alloy of gallium nitride (GaN) and aluminum
nitride (AlN), it is possible to displace emission wavelengths into the
extreme UV region, and the emission
wavelengths were tailored to the various target organisms in this way. Light
with a wavelength between 200 and 300
nanometers (nm), with a marked maximum of around 265 nm, is particularly
suitable for the purpose. The optimal
wavelength can easily be varied depending on the microorganism in question.
For the first disinfection tests, in still
water, the scientists developed a UV-LED
module with an emission wavelength of 268 nm. Deionized water, tap
water, and clarified waste water were infected with spores of the bacterium
Bacillus subtilis and irradiated with various doses of UV-C light. Subsequent investigation showed that the Bacillus subtilis spores were deactivated at least as efficiently using UV-C LEDs as with the usual low-pressure
mercury-vapor lamps.
The more compact second-generation module uses concentrically arranged UV LEDs with an emission wavelength of 282 nm. In addition, the
sterilizer is fitted with a through-flow unit, a UV-reflecting block of aluminum with a snail-shell–like channel for water; this could certainly be made
out of glass for the marine aquarium hobby.
The scientists are now working to increase the capacity and efficiency
of the UV LEDs. At present, their efficiency is still only a few percent and
their output in the milliwatt range. If this can be increased, then there may
in future be a very promising alternative to the usual mercury-vapor lamps.
UV LEDs require no warm-up phase, and are long-lived, very compact, and
non-toxic. In addition, they can be run at low voltages, so that they could
be installed even in independent solar-powered systems, for example for
purifying drinking water.
—Source: IDW
