How is the ultraviolet disinfection process applied to reclaimed water treatment?

Disinfection effect Ultraviolet rays have a good inactivation effect on pathogenic microorganisms in water. The disinfection dose of secondary treatment water is generally 15-22mws/cm2, and the disinfection dose of reclaimed water is 24-30mws/cm2. Ultraviolet rays act on the DNA of microorganisms to form thymine dimers and inhibit the replication of DNA. However, ultraviolet disinfection does not have the ability to continuously sterilize bacteria. Some microorganisms undergo photoreactivation after being irradiated by visible light. The researchers suggest that if the sewage is reused after treatment, UV disinfection needs to be used in combination with chlorine/chlorine dioxide.

Resurrection of microorganisms in water after disinfection The mechanism of ultraviolet disinfection is that the DNA of microorganisms is irradiated by ultraviolet rays to form thymine dimers, so that they cannot replicate themselves and die or are eliminated by the bacterial immune system. Current research shows that the activity and value-added ability after photoreactivation can be significantly improved. UV-chlorine disinfection has better inactivation effect and can control photoreactivation.

When the UV irradiation dose is 5.4 mJ/cm2, after adding 2.5mg/L chlorine and reacting for 10 minutes, the coliform bacteria in the effluent<20CFU/L, and no photoreactivation phenomenon. The formation of by-products Sewage contains a lot of organic matter. When chlorination is used for disinfection, it will not only consume more available chlorine but also generate trihalomethanes (THMs) 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 the 300μg specified in GB18918-2002.

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