Ultraviolet Disinfection Principle

The principle of ultraviolet (UV) sterilization is to utilize the ability of UV light of appropriate wavelengths to destroy the molecular structure of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) in microbial cells, causing cell death and/or regenerative cell death, thus achieving sterilization. Experiments have shown that the effective wavelength range for UV sterilization can be divided into four different bands: UVA (400–315 nm), UVB (315–280 nm), UVC (280–200 nm), and vacuum ultraviolet light (200–100 nm). Of these, only UVA and UVB can penetrate the ozone layer and clouds to reach the Earth's surface. In terms of sterilization speed, UVC is within the microbial absorption peak range and can kill viruses and bacteria within 1 second by destroying the DNA structure of microorganisms. UVA and UVB, however, are outside the microbial absorption peak range and have a very slow sterilization speed, often requiring several hours to achieve a sterilization effect. In practical engineering applications, during the few seconds of hydraulic residence time (irradiation), this portion is essentially ineffective ultraviolet light. Vacuum ultraviolet light has extremely weak penetrating power, requiring the use of highly transparent quartz for the lamps and sleeves. It is generally used in the semiconductor industry to degrade TOC in water and is not used for sterilization and disinfection. Therefore, the ultraviolet disinfection mentioned in water supply and drainage engineering actually refers to UVC disinfection. Ultraviolet disinfection technology is based on modern epidemiology, medicine, and photodynamics. It utilizes specially designed, high-efficiency, high-intensity, and long-life UVC band ultraviolet light to irradiate flowing water, directly killing various bacteria, viruses, parasites, algae, and other pathogens in the water, thus achieving disinfection. Research shows that ultraviolet light primarily kills microorganisms (bacteria, viruses, spores, and other pathogens) by radiating damage and disrupting their nucleic acid function, thereby achieving disinfection. The effect of ultraviolet light on nucleic acids can lead to bond and chain breakage, interstrand cross-linking, and the formation of photochemical products, thereby altering the biological activity of DNA and preventing microorganisms from replicating. This ultraviolet damage is also lethal. Ultraviolet (UV) disinfection is a physical method that does not add any substances to the water and has no side effects, which is why it is superior to chlorination disinfection. It is usually used in combination with other substances. Common combination processes include UV+H2O2, UV+H2O2+O3, and UV+TiO2, which can achieve better disinfection results.