Photocatalytic Oxidation – “Cold Burning”

Ultraviolet radiation is not visible to the human eye, and it encompasses the following areas of the spectrum according to the definition in DIN 5031-7.

The Light Spectrum and Its Use in Photocatalytic Oxidation

Long-Wave (black light) UV-A (380 - 315 nm)
Medium-Wave UV (Dorn radiation) UV-B (315 - 280 nm)
Short-Wave UV UV-C (280 - 200 nm)
Vacuum UV UV-C (200 - 100 nm)
Extreme UV EUV (121 - 10 nm)

UV radiation with a wavelength under 300 nm is used to kill microorganisms on account of its having a high density of energy. UV-C light’s highly dense energy causes a corresponding reaction in microorganisms. After this amount, at a wavelength of 254 nm, bacteria, fungi, molds, and virus are killed or damaged, depending on the dose of radiation, by having their DNA destroyed and further cell division is halted.

Below 200 nm, radiation has waves that are so short and so powerful they are absorbed by oxygen (02), which results in it being split into two oxygen radicals (2O). Both of these oxygen radicals always subsequently react with one other oxygen molecule (O2), and ozone is created (O3). This process is called photocatalytic oxidation or “cold burning” and is used when cleaning exhaust air from the food services and industry.

Photocatalytic Oxidation for Treating Exhaust Air in the Food Service Industry

In the food service industry, exhaust air is air that flows from the kitchen either naturally or under pressure. UV-C ozone systems, which are built into ventilation hoods or duct units, are used to eliminate kitchen exhaust, which is mostly composed of steam and odors from food and grease –  or “fumes.” Next, the organically polluted exhaust is passed through grease filters and subsequently passes over UV-C ozone lamps, which are installed in the hood or the duct unit. As part of this process, organic particles from exhaust air are “cracked” by high energy UV-C radiation. At the same time, oxygen radicals are split in order to make ozone (O3), which – after a short reaction time – breaks down into oxygen again. As part of this decomposition process, the molecules that had been previously “cracked” are oxidized via the broken down ozone. This reaction takes place in the ventilation system connected to the hood or in the duct unit. For optimal reactions, we recommend 2- to 3-second air duct systems. Using this method greatly reduces grease deposits in the ducts and ventilators. At the same time, the amount of kitchen odors are reduced by up to 95%.

The advantages of photocatalytic oxidation for exhaust in the food services industry:

  • Eliminating exhaust filled with germs and odors
  • Fire protection relating to decreasing the amount of grease and disposing of it
  • It is possible to install at any time (depending on the specific ventilation system)
  • Flexible possibilities for application
  • The exhaust can be used for heat recovery without incurring high costs
  • Low installation costs – it is easy to retrofit into existing ventilation hoods or air ducts

Photocatalytic Oxidation to Treat Industrial Exhaust Air.

Industrial exhaust air is exhaust that results in the wake of industrial activities, and it must correspond to the legal requirements listed in the TA Luft regulations or in BlmSchG, the German Technical Regulations on Emissions.

Exhaust from industrial deep fryers, bakery production lines, smokehouses, etc. is treated and purified using UV-C ozone systems the same as exhaust air primarily contaminated with H2S and DMS, i.e., exhaust from processing plants (slaughterhouses, rendering plants, waste water treatment plants, pumping stations, etc.); pharmaceutical plants; or plants with exhaust air containing organic components, such as the manufacturing industry (paint shops, processing polyethylene terephthalate) or the pharmaceutical industry (producing heparin, processing bromoacetate esters, etc.).

Also, industrial use requires that exhaust must flow over the UV-C ozone lamps at a rather slow speed. The process of photocatalytic oxidation is the same as the process described above for the food service – with the difference that a significantly larger amount of exhaust must be processed in industrial sectors.

Photocatalytic purification alone is not sufficient for all types of organically contaminated exhaust. For this type of exhaust, various exhaust purification systems may be combined, such as air scrubbers for eliminating ammonia or high-performance air scrubbers developed for effective preliminary separation of tar in smokehouses.

Our industrial exhaust purification systems have long since become the standard for a wide variety of industrial sectors, and after coming to an agreement with a potential customer, it is possible to visit this type of system. In addition to purely “industrial” use, individual custom-made solutions also have merit, such as comprehensive systems for purifying restroom exhaust in large building complexes, for example.

The advantages of photocatalytic oxidation for treating industrial exhaust air:

  • Decreasing odors and overall carbon content, according to TA Luft
  • Up to 100% resistance to humidity
  • On/off system, preheating not necessary
  • Space-saving system – lightweight and easy to install on roofs

Decontaminating Spaces – Eliminating Odors and Germs

Today, odors in the environment tend to be very quickly perceived as disruptive. Bad odors often appear unexpectedly – for example, because of a change in the air ducts, because of specific hygienic conditions, or simply resulting from a change in weather. Naturally, the associated bacterial contamination of the air or surfaces is linked to the odors. For effectively reducing odors and germs, oxytec has developed stationary and mobile devices that are specialized for various uses, applications, and goals and are based on air extraction systems from the food services and industry. In these devices, the air to be purified – generally air from the room – passes over UV-C ozone lamps. As this happens, the air is cleaned of germs and is also filled with ozone via the process of photocatalytic oxidation, described above.  Here again, ozone is produced using high-energy radiation under 200 nm. With the help of ventilators installed in the devices, the ozone that is produced is dispersed into the room so that photocatalytic oxidation occurs on the room’s surfaces and in its air – instead of in the closed system of the air ducts. The odors and microorganisms – such as germs, bacteria, and mold spores – that are found on surfaces are also simultaneously rendered inactive in a completely natural way, as if by the sun’s radiation. Again, what remains after oxidation is oxygen for fresh, clean air.

To effectively eliminate odors using ozone, devices are used that do not allow people to be present when the devices are in use. Alternatively, devices with “partial” ozone can be used, so that it is safe for people to be present during use.

For applications such as applying ozone/sterilizing spaces and surfaces, these devices can be controlled remotely by ozone sensors or measuring devices. See also the information on disinfecting with ozone.

Typical fields in which decontamination of odors and germs is used:

  • Cleaning vehicles (odors inside vehicles, upholstery, air-conditioning, etc.)
  • Hotel rooms
  • Ski locker rooms
  • Restrooms
  • Rooms with waste containers
  • Libraries
  • Rooms contaminated with odors in the public and private spheres

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