Viruses, ozone disinfection

Disinfection alone, or a combination of disinfection and filtration, can achieve the minimum mandatory removals and/or inactivation of 99.9% Giardia cysts and 99.99% enteric viruses. Primary disinfection systems that use ozone, chlorine, or chlorine dioxide can achieve greater than the above-stated inactivation of enteric viruses when 99.9% inactivation of Giardia cysts is attained. Therefore, achieving sufficient Giardia cyst inactivation can ensure adequate inactivation of both types of organisms. This is not the case, however, when using chloramination because it is such a poor virucide. 

Studies of the combined process involving ultrasound and ozone have shown faster degradation rates for a range of chemical contaminants than either method applied alone. Sonolytic ozonation has also been found effective for the disinfection of water but in these cases sonication also has a number of direct effects on the bacteria and viruses (see above). 

Ozone applications in gas/water/solid systems cover a wide range of media such as sludges, soils, adsorbents and catalysts. Disinfection, which can be regarded as a three-phase system, is a well-described and established application (see Section A 3.2.1 and 3.3.2). The preozonation for particle removal is discussed frequently, especially in the treatment of surface water, where different organic (e. g. bacteria, viruses, algae, suspended organic matter) and inorganic (e. g. silica, aluminum and iron oxides, clay) particles can be present (see Section A 3.2.4). 

Ozone (O3) can also be used to disinfect wastewater. It s effective at killing viruses that chlorine can t kill. It s more expensive, however, and doesn t provide the residual protection against bacteria. 

Disinfection. Disinfection is the general method of killing pathogens (bacteria, viruses, parasites). The most common method is chlorination of the water with sodium hypochlorite bleach. Less frequently used is ultraviolet light or ozone aeration. Water may be boiled at home for disinfection in cases of emergency. 

Disinfection of water supplies commonly uses oxidizing agents such as chlorine or ozone to kill microbial pathogens (bacteria and viruses). Chlorine gas forms chloric(i), HOCl, acid in water. The chlorate (i) ions, CIO, formed in water are responsible for its germicidal properties. Use of chlorine as a disinfectant is of concern due to its ability to oxidize other species, forming harmful by-products (for example, trichloromethane, CHCI3). 

Concern over possible production of toxic organochlorine compounds by water chlorination processes has increased interest in ozonation. Furthermore, ozone is more destructive to viruses than is chlorine. Unfortunately, the solubility of ozone in water is relatively low, which limits its disinfective power. 

---