Ultraviolet rays mainly cause the death of microorganisms through radiation damage to microorganisms (bacteria, viruses, spores and other pathogens) and the function of destroying nucleic acids, so as to achieve the purpose of disinfection. The effect of ultraviolet rays on nucleic acids can lead to bond and chain breaks, inter-strand crosslinks, and formation of photochemical products, etc., thereby changing the biological activity of DNA and making microorganisms unable to replicate themselves. This ultraviolet damage is also fatal damage. Ultraviolet disinfection is a physical method, it does not add any substances to the water, and has no side effects. This is where it is superior to chlorination disinfection, and it is usually used in combination with other substances.
At present, only artificial mercury (alloy) light sources can output sufficient UVC intensity for engineering disinfection. The ultraviolet disinfection lamp tube is made of quartz glass. According to the difference in the vapor pressure of mercury inside the lamp tube after lighting and the difference in the output intensity of ultraviolet light, the mercury lamp is divided into three types: low-pressure low-intensity mercury lamp, medium-pressure high-intensity mercury lamp lamps and low-pressure high-intensity mercury lamps. The bactericidal effect is determined by the irradiation dose received by microorganisms, and is also affected by the output energy of ultraviolet light, which is related to the type of lamp, light intensity and use time. As the lamp ages, it will lose 30%-50% of its intensity.
The ultraviolet irradiation dose refers to the amount of ultraviolet light of a specific wavelength required to achieve a certain bacterial inactivation rate: irradiation dose = irradiation time × UVC intensity, the greater the irradiation dose, the higher the disinfection efficiency. Due to the size requirements of the equipment, the general irradiation time is only a few seconds, therefore, the UVC output intensity of the lamp has become the most important parameter to measure the performance of ultraviolet disinfection equipment. In urban sewage disinfection, the general average exposure dose is above 300J/m2. Below this value, there may be photoreactivation phenomenon, that is, the germs cannot be completely killed, and when they flow out of the channel and are irradiated with visible light, they will be resurrected again, which reduces the bactericidal effect. The higher the sterilization efficiency requirements, the greater the required irradiation dose. The main factor that affects the microorganisms receiving sufficient ultraviolet radiation dose is the light transmittance. When the UVC output intensity and irradiation time are constant, the change of the light transmittance will cause the change of the actual dose received by the microorganisms.
(1) Ultraviolet disinfection does not require chemicals and does not produce THMs disinfection by-products.
(2) Ultraviolet disinfection lamps have fast bactericidal effect and good effect.
(3) No odor, no noise, and does not affect the taste of water.
(4) Easy operation, simple management, low operation and maintenance costs.
Most ultraviolet devices use traditional low-pressure ultraviolet lamp technology, and some large water plants use low-pressure high-intensity ultraviolet lamp systems and medium-pressure high-intensity ultraviolet lamp systems. Due to the generation of high-intensity ultraviolet rays, the number of lamp tubes may be reduced by more than 90%, thus the floor area is reduced, installation and maintenance costs are saved, and the ultraviolet disinfection lamp is also suitable for effluent with poor water quality.