Application of ultraviolet light and sterilization principle
According to the wavelength, ultraviolet (UV) light is usually divided into UVA (315 ~ 400 nm), UVB (280 ~ 315 nm), UVC (200 ~ 280 nm). UVC band is also called “sun blind” band, because of the strong absorption of ozone in the atmosphere, there is almost no ultraviolet light in the near earth solar spectrum.
The main applications of UVC include disinfection / purification of water / air / surface, analytical instruments (spectrophotometry, liquid chromatography, gas chromatography, etc.), and mineral analysis. UVC band has short wavelength and high energy. It can destroy the molecular structure of microbial organism (bacteria, viruses and other pathogens) cells in a short time. By destroying the DNA and RNA of microorganisms to prevent their reproduction, it can achieve efficient and rapid broad-spectrum sterilization effect, so as to sterilize water, air and surface of objects, and make cells unable to regenerate. Therefore, it is widely used in sterilization of water and air Disinfection. The data show that UVC ultraviolet radiation intensity of 30 MW / cm2 can kill almost 100% of most bacteria in one second. The effect is very significant, which can be widely used in medical and health field. In the field of personal health and family health, ultraviolet light can be used for disinfection of water cups, bowls and chopsticks, air purification and sterilization, killing insects, sterilization and deodorization of shoes and socks, and disinfection of baby bottles, etc.
Ultraviolet germicidal efficacy
The time and dose of UV sterilization are different according to the types of microorganisms. Different bacteria have different absorption peaks. For example, the maximum absorption wavelengths of DNA and Escherichia coli are 265 nm, while those of Cryptosporidium and bacteriophage are 261 nm and 271 nm respectively. Therefore, the required sterilization time should be different. When the UV radiation intensity was 3 × 104 μ w / cm2, the time needed to kill virus, bacteria, mould spores and algae bacteria was 0.1 ~ 1.0 s, 1.0 ~ 8.0 s, 5.0 ~ 40.0 s, respectively. According to the research team of Dong Xiaoping, an expert from the Institute for virus disease control and prevention of the Chinese Center for Disease Control and prevention, the SARS virus can be killed in 30 minutes by UVC irradiation with an intensity of more than 90 μ w / cm 2.
Ultraviolet dose plays an important role in the sterilization process. The UV dose can be expressed as the product of UV intensity and irradiation time. Under the condition of sufficient ultraviolet dose, the inactivated virus bacteria will not revive, but when the dose is insufficient, many virus bacteria which are inactivated by ultraviolet radiation can repair their damaged structures with the help of light. When the UV dose is the same, high intensity, short time or low intensity and long time irradiation can be used to achieve the purpose of sterilization. It takes about 30 MJ / cm2 to kill 1 × 104 cells / ml of spirobacillus, and 70 MJ / cm2 to kill the same number of spores.