Ultraviolet light disinfection

O. K. Scheible, Development of a rationally based design protocol for the ultraviolet light disinfection process. Journal WPCE 59, 25-31 (1987). 

Severin BE, Suidan MT, Engelbrecht RS (1983) Effects of temperature on ultraviolet light disinfection. Environ Sd Technol 17(12) 717-721... 

Disinfeetion. Chlorine, as gaseous chlorine or as the h5rpochlorite ion, is widely used as a disinfectant. However, its use in some cases can lead to the formation of toxic organic chlorides, and the discharge of excess chlorine can be harmful. Ozone as an alternative disinfectant leads to products that have a lower toxic potential. Treatment is enhanced by ultraviolet light. Indeed, disinfection can be achieved by ultravifflet light on its own. 

Heat is the most reliable method of virus disinfection. Most human pathogenic viruses are inactivated following exposure at 60°C for 30 minutes. The virus of serum hepatitis can, however, survive this temperature for up to 4 hours. Viruses are stable at low temperatures and are routinely stored at -40 to -70°C. Some viruses are rapidly inactivated by drying, others survive well in a desiccated state. Ultraviolet light inactivates viruses by damaging their nucleic acid and has been used to prepare viral vaccines. These facts must be taken into account in the storage and preparation of viral vaccines (Chapter 15). 

In order to achieve complete destruction of biological contaminants in water through sonication very high ultrasonic intensities are necessary. Unfortunately this makes the technique expensive to use for general microbiological decontamination. However over the last two decades some conventional disinfection techniques involving chemicals, ultraviolet light and heat treatment have become less effective as some bacteria become more resistant. Such processes have become a focus for the use of sonication as an adjunct to other techniques. 

How are the disinfecting properties of ultraviolet light and ozone similar to each other ... 

Another disinfection technique consists in passing the effluent through an array of ultraviolet lights. Ultraviolet radiation kills microorganisms but does not otherwise affect water. 

The physical agents of disinfection that have been used include ultraviolet light (UV), electron beam, gamma-ray irradiation, soniflcation, and heat (Bryan, 1990 Kawakami et al., 1978 Hashimoto et al., 1980). Gamma rays are emitted from radioisotopes, such as cobalt-60, which, because of their penetrating power, have been used to disinfect water and wastewater. The electron beam uses an electron generator. A beam of these electrons is then directed into a flowing water or wastewater to be disinfected. For the method to be effective, the liquid must flow in thin layers. 

In the context of how we use the term, intensity refers to the intensive property of the disinfectant. Intensive properties, in turn, are those properties that are independent of the total mass or volume of the disinfectant. For example, concentrations are expressed as mass per unit volume the phrase per unit volume makes concentration independent of the total volume. Hence, concentration is an intensive property and it expresses the intensity of the disinfectant. Another intensive property is radiation from an ultraviolet light. This radiation is measured as power impinging upon a square unit of area. The per unit area here is analogous to the per unit volume. Thus, radiation is independent of total area and is, therefore, an intensive property that expresses the intensity of the radiation, which, in this case, is the intensity of radiation of the ultraviolet light. 

The BSE agent is smaller than most viral particles and is highly resistant to heat, ultraviolet light, ionizing radiation, and common disinfectants that normally render viruses and bacteria inactive. It causes no detectable immune or inflammatory response in the host, and has not been observed microscopically. 

Prions are very difficult to inactivate. Agents that completely denature protein, such as bleach and strong alkali or acid (see the Dementias section later in the chapter) are effective, but ultraviolet light, routine formalin fixative, and standard disinfectants fail to eradicate prions. 

Treated wastewater from municipal sewage plants requires a treatment with chlorine before discharge into a river, at least in the warmer months of the year. Because the residual chlorine can kill the flora and fauna of the river, the treated wastewater is usually treated further with sulfur dioxide or sodium bisulfite to remove the chlorine.128 This seems like an ideal place to use alternative methods of disinfection, because no residual activity is needed or desired. Disinfection with ultraviolet light is now a viable alternative.129... 

The sanitation of clean areas is particularly important They should be cleaned frequently and thoroughly in accordance with a written programme approved by the quality control department Where disinfectants are used, more than one type should be employed, with periodic alterations. Monitoring should be regularly undertaken in order to detect the emergence of resistant strains of microorganisms. In view of its limited effectiveness, ultraviolet light should not be used as a substitute for chemical disinfection. 

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