Bacteria, ozone disinfection

Bacteria, ozone disinfection, 616 Bactericides, hydrogen peroxide, 623 Baeyer-Vilhger oxidation, 538-56, 551-66 ketones, 784-7 tin(lV) chloride, 786-7 peroxyester determination, 700-1 Base-catalyzed reactions... 

Disinfection. Ozone is a more effective broad-spectmm disinfectant than chlorine-based compounds (105). Ozone is very effective against bacteria because even concentrations as low as 0.01 ppm are toxic to bacteria. Whereas disinfection of bacteria by chlorine involves the diffusion of HOGl through the ceU membrane, disinfection by ozone occurs with the lysing (ie, mpture) of the ceU wall. The disinfection rate depends on the type of organism and is affected by ozone concentration, temperature (106), pH, turbidity, clumping of organisms, oxidizable substances, and the type of contactor employed (107). The presence of oxidizable substances in ordinary water can retard disinfection until the initial ozone demand is satisfied, at which point rapid disinfection is observed. 

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). 

Several operations may be employed to treat water prior to use. Aeration is used to drive off odorous gases, such as H2S, and to oxidize soluble Fe2+ and Mn2+ ions to insoluble forms. Lime is added to remove dissolved calcium (water hardness). A12(S04)3 forms a sticky precipitate of Al(OH)3, which causes very tine particles to settle. Various filtration and settling processes are employed to treat water. Chlorine, Cl2, is added to kill bacteria. Formation of undesirable byproducts of water chlorination may be avoided by disinfection with chlorine dioxide, C102, or ozone, 03. 

The primary purpose of the Sterilamp tube in air-conditioning systems has been to destroy microorganisms (22). Tests on the effect of 1 to 2 p.p.m. by voliune of ozone on E. coli sprayed into an air duct revealed that the organisms were not destroyed. This would confirm the data of Elford and Van den Ende ( ) that ozone is a poor disinfectant of air at low relative humidity. At high relative humidity these authors found that as low as 0.04 p.p.m. by volume destroyed bacteria dispersed in an aerosol. This would also agree with the results reported here, that organisms on surfaces and seeded on Petri plates can be destroyed by minute amounts of ozone. 

The time for the water to move through the two compartments, A and B, of the ozonation chamber is normally 5 minutes, or 2.5 minutes per compartment. This is long enough when the water treatment aims mainly at disinfection it provides a margin of safety sufficient to ensure the complete destruction of the pathogenic bacteria which may be found in the most polluted of the Swiss water supplies. 

Table 12 shows the typical LRV values obtained using a polymeric and ceramic microfilter. Sterile filtration requires 100% bacteria retention by the membrane, whereas in many industrial bacteria removal applications the presence of a small quantity of bacteria in the filtrate may be acceptable. For example, drinking water obtained by microfiltration may contain nominal counts of bacteria in the filtrate which is then treated with a disinfectant such as chlorine or ozone. The use of ceramic filters may allow the user to combine the sterile filtration with steam sterilization in a single operation. This process can be repeated many times without changing filters due to their long service life (5 years or longer). 

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. 

Aeration. Water is drawn from the bottom of the sand filters and is aerated by spraying. The purpose of this process is to remove objectionable odors and tastes. Disinfection. In the final stage chlorine gas is injected into the water to kill harmful bacteria before the water is distributed to the public. Ozone is also used to disinfect water. In emergencies, water may be disinfected by simply boiling it for a few minutes. 

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