The airborne microorganisms are accessible for the UV-rays, while the conventional means of air disinfection are useless or not applicable. No matter how indispensable and important they may be in the field of disinfection of medical equipment.
Disinfection procedures of packaging materials in the food industry, as well as manufacturing
Possibilities and problems in the area of disinfection as mentioned in the following are dependent on so many conditions related to plants, that the stated values are only usable as a first step towards the specification of a disinfection plant. As many as possible of the theoretically stated values should be compared through examination in practice.
The result of a surface disinfection depends heavily on the character of the material to be freed of germs. Through UV-radiation it is – as already mentioned – only possible to inactivate the bacteria that are reached by radiation. This means that for the application of radiation for disinfection it is important to consider that disinfection of solid objects only succeeds, when the total surface of the object is exposed to radiation, and when this surface has no irregularities where bacteria can hide and thus be protected from radiation. As, however, roughness of surface causes formation of micro-shadowiness many bacteria may escape. Bacteria located deeply are generally not reached at all – due to the low penetration depth of radiation. However, because of bends the serious effect of forming of micro-shadowiness is somewhat reduced.
In practice, disinfection – or better still – the removal of bacteria from solid surfaces and packaging materials (which may be of widely varying artificial materials: glass, sheet metal, cardboard, folio, etc.) must be carried out with intensive direct radiation.
Often it is found that further disinfection with ordinary disinfection means is useful for a good result. Besides, it is important that once sterilised material may be kept very much free of germs on the further road of manufacturing with UV-radiation, as the germ contents of the air is strongly reduced through the simultaneously obtained air radiation. Should the disinfection be limited on similar materials, protection of staff is relatively simple: The plant is completely protected. Also indirect (reflected) radiation should not reach outside.
With the use of air disinfection, the effect is that the total level of airborne bacteria in a room is considerably reduced. As the natural circulation of air at some point leads all layers of air once through the area of radiation thereby preventing contagious sources from the air, which are of considerable significance which plays a role for many illnesses and infections. However, one must be always be aware that bacteria-free air or even with a reduced number of germs does not in itself have any disinfection effect.
Water quality and disinfection
The quality of water has a decisive influence for the influence of the disinfection. Substances that make the water unclear can have influence on the efficiency. The advantage of UV-C radiation is that it is not depending the visible light. Decisive is, if the small particles in the water absorb or reflect the UV-C radiation, where this influences the degree of penetration. If the water quality is poor, the sterilisation can be improved by usage of active coal or sand filters. Obtaining the thresholds for drinking water, it is possible to get a full UV-C sterilisation without any problems at all!
This description covers a range of spore plants with about 8000 living kinds – varying from single-celled to larger types.
Some important groups are:
- Split algae (blue green algae)
- Diatomeen (Silicon algae)
- Green-, brown- and red algae
Algae contain chlorophyll, at times supplemented by other colouring matter, which means that they can nourish themselves through assimilation. UV-dose values for some types of algae are mentioned here. A remarkable feature here is the very high dosage, in some cases with potencies at higher levels than e.g. the dose for bacteria.
See also table:
Bacteria is a major group of single-celled plant organisms which multiply by division. They cause illness, fermentation, and aging. Fundamental forms for bacteria cells are:
- Ball (Coccus)
- Small rods (Bacillus and Bacterium in the most restricted sense)
- Corkscrew (Spirillum, Vibrio, Spirochete)
In favourable conditions, many bacteria form resistant lasting/permanent spores (these spore-producing bacteria are also collectively termed as bacilli (germs). Generally, spores are more resistant to high temperatures and UV-radiation than bacteria, which is why it is necessary to choose ten times the dose that would be necessary for the destruction of bacteria. Under favourable conditions, the spore develops into a new bacterial cell.
Yeast fungi are uni-cellar plant-like micro organisms (Sacharmyces and other relatives to snake fungi). They do not contain chlorophyll and differentiate themselves from mould by multiplying in a different way. Like some kinds of bacteria, yeast fungi can also form spores. In practice, yeast fungi are widely applied. The most important applications are beer yeast fungi (lower and upper yeast fungi), yeast fungi for raising bread, wine and food items (dried, pressed yeast fungus).
The pattern of yeast fungi reaction to UV-radiation is similar to that of mould fungi in which processes the aim is the destruction of the “wild” yeast fungi.
Mould this description covers a group of micro organisms, spread through spores. Mould fungi form cotton wool-like, entangled and puffball -like expanses on plant or animal matter (materia), causing a putrefying (rotting) process. Mould fungi are also seen as parasites causing illness in humans and animals.
Some kinds are:
- Head mould (mucor) on fruit and bread
- Flask (spadix) or pouring jugs (Aspergillus), on moist plant matter, fruit, bread, leather
- Brush mould (botrytis cinera), perishable fruit, especially strawberries and half ripening grapes.
Other kinds of moulds serve as the basis for Antibiotics. Here we shall just mention penicillin and streptomycin.
First mould fungi (and yeast fungi) show activation when radiated with small doses of UV. With larger doses they are killed, in which process the spectral effect is approximately the same as with the bacteria. Also here the spores are essentially more resistant than vegetative kinds.
This term covers a group of micro-organisms of largely unknown nature, all of which cause illnesses in humans, animals and plants. Vira are so small that bacteria-impermeable filters cannot trap them. Not until the use of the electron microscope, has it became possible to observe all kinds of vira. All vira have the characteristic of not thriving on dead matter, which is why they can only be cultivated in living substances. Vira are stopped in their action, when exposed to UV-C 253.7
There are important differences in the resistance towards UV-C radiation for the various kinds of micro-organisms. The percentage for dead bacteria is not proportional with the dose of radiation, where, however, they increase with an increasing dose. In the list a collection of the necessary doses for a certain effect of disinfection is given. The information is from current literature.
The values from various authors are at present remarkably deviant. This may be due to the different types of bacteria – different growth conditions and the temperatures concerned. Calculations based on the inactivation of micro-organisms show a variation in the interpretation of the conditions of radiation for necessary dose values.
This means that with e.g. a radiation value E, which over a certain progress of time T, reaches a certain effect of disinfection, arrive at the same result when the two factors vary, but their result E multiplied by T is the same. However, it is only possible to change the time T within certain boundaries, as the micro-organisms by excessively prolonged radiation and at a too low radiation value E, in the beginning will only be able to multiply, due to the fact that the UV-dose is too small. For these reasons, the desired effect of inactivation is achieved much later than this law stipulates. The surroundings, in which microorganisms are found, greatly influence the desired level of disinfection. In water e.g. there are coli-bacteria, which are 10 times more resistant than in air. Increased moisture content in the air greatly increases the necessary dose.