UV Radiation Process Description

The radiation dose absorbed by the water is the water s UV demand, which is analogous to chlorine demand and is quantified as the absorption of UV energy (at a wavelength of 253.7 nm) in a given depth of water. The measurement is most commonly expressed by the UV absorbance coefficient alpha  

In addition to intensity and UV demand of the water, the exposure time also affects the energy dosage that the target organisms absorb. Exposure time is controlled by the residence time of the water in the reactor. Continually maintaining the required residence time is not always possible, but the system design should maximize plug-flow operation. 

To prevent photoreactivation, the rule of thumb is to increase the dosage necessary to meet a required reduction in organism numbers. For example, if the disinfection criteria require a 3-log reduction of microorgaifism concentrations, the UV radiation system should be designed to provide a 4-log reduction. 

In this chapter, UV radiation for both disinfection and oxidation of organic contaminants is addressed. In the UV disinfection, common pathogens in the environment and 

UV germicide mechanisms are introduced. Basic principles of UV disinfection system design, installation, and operation considerations are presented. The concern about UV disinfection by-products is also discussed. In addition, the mechanisms of UV oxidation are addressed. Its applications on organic pollutants decomposing as an emerging water and wastewater treatment technology are discussed. 

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