Water treatment, ozone generator

Boron-doped diamond is electrically conducting and has found applications as electrode material in waste-water treatment, ozone generation, electroanalysis, and trace metal detection [ii]. Due to their exceptional chemical inertness and mechanical strength, diamond electrodes have been proposed for applications in extremely aggressive media such as strong acids or plasmas. See also -> carbon electrodes. 

Finally, BDD electrodes have also found extensive use in the areas of water treatment (ozone and hydroxyl radical generation), and organic and inorganic synthesis processes, but it is beyond the scope of this chapter to provide detailed information. The reader is directed to references [7,10] for further information. 

Contactor design is important in order to maximize the ozone-transfer efficiency and to minimize the net cost for treatment. The three major obstacles to efficient ozone utilization are ozone s relatively low solubility in water, the low concentrations and amounts of ozone produced from ozone generators, and the instability of ozone. Several contacting devices are currently in use including positive-pressure injectors, diffusers, and venturi units. Specific contact systems must be designed for each different application of ozone to wastewater. Further development in this area of gas-liquid contacting needs to be done despite its importance in waste treatment applications. In order to define the appropriate contactor, the following should be specified ... 

Figure 9 shows the details of a typical horizontal tube-type ozone generator. This unit is preferred for larger systems. Water-cooled plate units are often used in smaller operations. However, these require considerably more floor space per unit of output than the tube-type units. The air-cooled Lowther plate type is a relatively new design. It has the potential for simplifying the use of ozone-generating equipment. However, it has had only limited operating experience in water treatment facilities. 

Figure 13.3 A large ozone generator for water treatment producing 60kgh . (Courtesy Ozonia Ltd.)...

Full-scale waste water ozone treatment facilities may roughly be defined as systems with a ozone generation capacity of more than 0.5 kg per hour. They can be found in various applications in all branches of industry, treating almost all types of waste waters. The operating conditions used in waste water ozonation are dependent on the type of industry and the kind of waste water. They can be grouped according to ... 

Langlais B, Reckhow DA, Brink DR (Ed.) (1991) Ozone in Water Treatment - Application and Engineering. Cooperative Research Report. American Water Works Association Research Foundation Company Generate des Eaux and Lewis Publisher, Chelsea, MI, ISBN 0-87371-477-1. 

Since reaction mechanisms and experimental observations are not independent of the system in which they are made, the experimental set-up and how the experiment is run affect the outcome. That means that it must be clear how equipment and procedures affect the outcome when they are chosen. It also means that experimental set-ups and procedures from drinking water treatment cannot be applied on waste water without appropriate evaluation and vice versa. In general, an experimental set-up consists of an ozone generator, reactor, flow meters and on-line analysis of at least the influent and effluent ozone gas concentrations and ambient air monitor (Figure 2-1). Each set-up will be tailored to the experimental goals and the resources available. 

Horn R J, Straughton J B, Dyer-Smith P, Lewis D R (1994) Development of the criteria for the selection of the feed gas for ozone generation from case studies, in A K Bin (ed.) Proceedings of the International Ozone Symposium Application of Ozone in Water and Wastewater Treatment May 26-27 253-262, Warsaw Poland. 

The capital cost of ozone generators and associated monitoring and control systems is generally many times the cost of annual water treatment chemical programs. This has necessitated various lease schemes... 

Generation of zwitterion and hydroxy-hydroperoxide. (From Langlais, B. et al., Ozone in Water Treatment Application and Engineering, Lewis Publishers, Boca Raton, FL, 1991. With permission.)... 

Nitrite ion is an undesirable by-product of radiolysis in waters containing high nitrate concentrations, and regulatory limits exist regarding its acceptable concentration. The presence of nitrate does not preclude radiolytic water treatment. One approach that compensates for nitrite generation in high nitrate waters is ozone addition, discussed later. 

KOGELSCHA12 U (1987) Advanced Ozone Generation, in Stucki S (ed.) Process Technologies for Water Treatment, Plenum Press, New York 87-120. 

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