With the outbreak of COVID-19, UV disinfection has once again attracted the attention of the whole society. 1878, Arthur Downes and Thomas P. Blunt has published a paper explaining how to kill bacteria exposed to shortwave light. In medicine, ultraviolet light has been used as a mutagen to modify the DNA of cancer cells to treat diseases for more than 100 years.The history of using ultraviolet rays to disinfect water can also be traced back to the 1990s.
Before we talk about how it works, it is necessary to figure out what is UV. UV is an electromagnetic radiation with a wavelength from 10nm to 400nm. Its wavelengths between 200nm to 300nm are classified as fungicides, which means they can inactivate microorganisms such as bacteria, viruses and protozoa. UVC (ultraviolet light) with a wavelength range of 200 to 280nm does not irradiate the earth, but this light has the functions of sterilization, organic decomposition, photopolymerization, and sensing.
UV light at 254nm has the maximum germicidal effect against microorganisms. According to reports, a joint study between Japan’s Kobe University and Japanese LED component manufacturer Ushio shows that deep ultraviolet radiation with a wavelength of 222nm is harmless to human skin and eyes. Columbia University has also carried out related research, preliminary results show that far UVC with a wavelength of 222nm cannot penetrate the skin surface or eyes, is safe for the human body, and can also kill viruses.
Next let's see what factors can affect the effects of UV sterilization.
The effectiveness of germicidal ultraviolet rays depends on the time the microorganisms are exposed to ultraviolet rays, the intensity and wavelength of ultraviolet radiation. The longer the illumination time, the more accumulated light, and the better sterilization effect will be achieved. Therefore, to sterilize in a short time needs strong ultraviolet rays are. Besides, UV disinfection is called a line-of-sight technology. Therefore, if anything blocks the UV rays, including dirt, stains, and anything that casts shadows, then those “shaded or protected” areas will not be disinfected.
What pros&cons of UV disinfection.
1. Process without chemical substances, except for ultraviolet rays, no substances are added to the water.
2. No need to transport, store or handle toxic or corrosive chemicals.
3. Does not produce carcinogenic disinfection by-products.
4. Very effective in inactivating a variety of microorganisms (including the chlorine-resistant pathogens Cryptosporidium and Giardia).
1. Can be used in combination with oxidants (such as hydrogen peroxide) to decompose and destroy chemical pollutants in the water.
Cons: Ultraviolet rays are mainly harmful to the human body(except 222nm UVC).
Once the skin is irradiated by ultraviolet light, redness, swelling, itching, and scaling may occur in mild cases, and it may even cause skin cancer in severe cases. At the same time, ultraviolet light is also the "invisible killer" of the eye. Ultraviolet light can damage the epithelial cells of the cornea. If exposed to ultraviolet light for more than two hours, different degrees of foreign body sensation will appear. In severe cases, there will be tingling, tearing and even eye spasms. Blurred vision and other phenomena can cause conjunctivitis and keratitis, and long-term exposure can also cause cataracts. Therefore, pay attention to safety when using UV disinfection. Or you can choose to use filters to block other wavelengths of ultraviolet light to ensure your safe.
Principle of UV disinfection: UV inactivates microorganisms by destroying nucleic acids. Mainly 254 nm UVC cell RNA and DNA absorption. The absorption of ultraviolet energy will form new bonds between adjacent nucleotides, thereby forming double bonds or dimers. Dimerization of adjacent molecules (especially thymine) is the most common photochemical damage. The formation of large amounts of thymine dimers in the DNA of bacteria and viruses prevents replication.
Regarding the operation method and precautions of ultraviolet sterilization, please watch the video below.