Measurement and modeling of UV intensity inside a photoreactor for wastewater treatment

Abstract

Water availability and quality represent a major challenge facing water scarcity and pollution. The United Nations Organization predicts that 44% of the world population will live a severe water scarcity, in 2050. Countries located in sub-humid and semi-arid regions of the world will be especially concerned by this problematic. Water disinfection by Ultraviolet (UV) radiation is a rising technique in water treatments considering its simplicity and the weak risk of toxic byproducts formation. When UV radiation is absorbed by the cells of microorganisms, it damages the genetic material (DNA) within the cell in such a way that the organisms are no longer able to grow or reproduce, thus preventing the human illness cryptosporidiosis. DNA damage mainly results from irradiation at wavelengths within the UV-C region of the spectrum (200-280 nm) and is maximised at around 254 nm. This is the principle by which UV is used for disinfection. Time required to achieve a total disinfection depends both on the quality of water and the intensity of irradiation. Effective disinfection can be provided by a suitable intensity and duration of UV radiation to give a UV "dose" usually expressed in mJ/cm2 (= mW second/cm2, the product of UV intensity in mW/cm2 and contact time in seconds). The target dose will depend on the application, but a dose of 40 mJ/cm2 is commonly used for UV disinfection systems, validated for the broad spectrum inactivation of possible waterborne pathogens such as bacteria, viruses and protozoan parasites such as Cryptosporidium. The objective of this study is to present the state of art of different methods of intensity measurement and modeling, and the use of MPSS model to evaluate the UV intensity distribution inside the photoreactor.