Ultraviolet (UV) light has powerful germicidal effects and has been used to sterilize rooms and surfaces for decades. It is more effective than chlorine at killing harmful pathogens.
The UV wavelength that is most effective for killing microorganisms is 254 nm, referred to as the germicidal spectrum. The ability to kill bacteria, viruses and other microorganisms depends on the irradiance or fluence rate that is applied.
Inactivation of Viruses and Bacteria
UV radiation is effective against viruses and bacteria because it destroys their nucleic acids, which contain the information they need to reproduce. This occurs by photo-chemical reactions that cause specific thymine dimers in DNA and uracil dimers in RNA. As a result, the microorganism is unable to replicate and eventually dies.
The inactivation of viruses and bacteria by UV-C sterilization is dependent on the type of virus, the viral load and the environmental conditions (temperature, relative humidity). The survival fractions of four bacteriophages were investigated as a function of the UV dose and the percent RH. The results showed that the survival of ssRNA bacteriophage MS2 and dsRNA bacteriophage phi X174 were inversely proportional to the UV dose. In addition, the survival of ssRNA bacteriophage phi C229 was proportional to the UV dose.
Commercially available overhead far-UVC lamps have been shown to be capable of inactivating airborne S. aureus bacteria in an enclosed space in a few minutes. This is significantly faster than conventional chemical disinfectants.
UVC can also be used to sterilize medical equipment and to decontaminate surfaces. It has been found to be effective against Clostridium difficile spores, Adenovirus DNA and Adenovirus proteins. In addition, it has been used to sterilize non-critical patient care items and to reduce the number of spores of the human respiratory pathogen B. pumilus in the air of hospital rooms.
Sterilization of Water
The sterilization of water by UV light is used to control the spread of disease, such as tuberculosis, which is transmitted through contaminated drinking water. The process can also be used to disinfect equipment in laboratories, such as pipettors and glassware. UVGI is an alternative to other methods of disinfecting water, such as chlorine. There is no chemical residue left behind, which makes the method more environmentally friendly.
The UV radiation inactivates microorganisms by causing chemical changes to their nucleic acids. These changes inhibit the cells’ ability to reproduce, which destroys the organisms. The optimum UV dose for effective disinfection depends on the type of UV light and water quality. Water with dissolved organic matter, certain inorganic contaminants, such as iron, sulfites and nitrites, or suspended particulate material (turbidity) can absorb UV radiation and shield microorganisms from it, reducing the effectiveness of disinfection.
In addition, if the equipment is not properly maintained, the UV dose may be reduced over time as material builds up on the quartz sleeve or the rays are blocked by the water flow. Since the UV only works in its direct path, the device must be carefully aligned with the object or surface you want to sterilize. It’s also important to ensure the UV doesn’t interfere with any other materials, such as rubber, plastic, or insulation, as it can break down or discolor these substances.
Sterilization of Food
Although the food industry uses a variety of chemical sanitizers, germicidal UV irradiation is becoming a more common method for enhancing the safety of fresh produce. Studies have shown that this physical intervention treatment significantly reduces the number of pathogens on the surface of foods, in the air, and inside produce. It also avoids undesirable quality changes and the release of toxic disinfection byproducts.
Compared to other technologies that change the genetic structure of products or equipment, UV-C sterilization is relatively noninvasive. It has the advantage of being fast and easy to use. It is also used in commercial kitchens to sterilize conveyor belts, storage containers and other working surfaces. It can also be used in meat and seafood processing to disinfect water and equipment for washing raw products and rinsing carcasses.
Studies have found that UV irradiation can significantly reduce the presence of bacteria, yeast and fungus on the surface of fruits and vegetables. In a study on green onions, UVGI was more effective than either cold or mild heat in killing microorganisms. In addition, it was found that a combination of UVGI with agitation (washing) produced a more uniform reduction in surface contamination. The same combination of treatments also showed a significant reduction in contamination of fresh-pressed juices. In fact, this combination has become the standard of practice in many juice companies.
Sterilization of Medical Devices
UV sterilization works by breaking down the chemical bonds and scrambling the structure of DNA, RNA and proteins that are required for microorganisms to multiply. This prevents them from causing an infection or producing toxins in their host organism. It also prevents them from performing vital functions such as absorbing nutrients, transporting ions and creating new cells.
When used in conjunction with decontamination, UV sterilization is effective against a broad range of different viruses, bacteria and other pathogens. It can be used on medical devices, food processing equipment, storage containers and work surfaces. The effectiveness of UV-C on different surfaces is affected by the surface type, its age, the level of organic material present and the distance between the UV-C light device and the surface being sterilized.
A major benefit of UV-C disinfection is that it can be used on surfaces that cannot be sterilized with heat or chemicals. This includes surfaces that are made of plastic, wood or glass and that are prone to corrosion. It is also effective in hard-to-reach spaces that are difficult to clean by hand.
In addition to being useful for sterilizing medical devices and food processing equipment, UV-C disinfection is often used to improve indoor air quality in schools, hospitals and other commercial buildings. This is especially important during the COVID-19 pandemic as people are being encouraged to spend more time indoors. The use of portable UV-C sterilization devices has become commonplace to kill viruses, bacteria, molds and yeast in the air, water and on food, including milk, eggs, fruit, vegetables, money and paper.