Ultraviolet ray has a good inactivation effect on pathogenic microorganisms in water. The disinfection dose of secondary treatment effluent is generally 15-22mws/cm2, and the disinfection dose of reclaimed water is 24-30mws/cm2. Ultraviolet rays act on microbial DNA to form thymine dimer, which prevents DNA replication. However, ultraviolet disinfection has no ability to continue sterilization, and some microorganisms undergo light reactivation after being exposed to visible light. The researchers suggest that if the sewage is reused after treatment and sterilized by ultraviolet, it should be used together with chlorine/chlorine dioxide.

Resurrection of microorganisms in water after disinfection

Microwave electrodeless Ultraviolet water treatment equipment The mechanism is that the DNA of microorganisms can generate thymine dimer after being irradiated by ultraviolet light, which makes them unable to replicate and die or be eliminated by the immune system of bacteria. Current research shows that the activity and value-added ability can be significantly improved after photoreactivation. UV chlorine disinfection has good inactivation effect and can control photoreactivation. When the UV irradiation dose was 5.4 mJ/cm2, 2.5 mg/L chlorine was added and reacted for 10 min, the effluent coliform group was less than 20 CFU/L, and there was no light reactivation.

Formation of by-products

Sewage contains more organic substances. When chlorination is used, not only more effective chlorine will be consumed, but also trihalomethanes (THMs) will be generated as carcinogenic by-products. Ultraviolet disinfection will not produce by-products. With the increase of irradiation dose, the content of formaldehyde in water will increase slightly, but it is still lower than 300 specified in GB18918-2002 μ g。