Water And Wastewater Treatment Technologies Measurement And Control

Favorable operational economics and good management practices require high levels of control of the ozonation system. Depending on the specific process of ozone applications, plant size, and design philosophy, the control system may be simple or complex. The trend in Europe is toward highly sophisticated and

Several parameters should be measured to provide a fully operable ozonation system. There should be a means of providing full temperature and pressure profiles of the ozone generator feedgas from the initial pressurization (by fan, blower, or compressor) to the ozone generator inlet. Moisture content is also important. There should be a means of measuring the moisture content of the feedgas to the ozone generator. This procedure should be conducted with a continuously monitoring dew-point meter or hygrometer. Other parameters that

• Temperature, pressure, flow rate, and ozone concentration of the ozonecontaining gas being discharged from all the ozone generators. This is the only effective method by which ozone dosage and the ozone production capacity of the ozone generator can be determined.

• Power supplied to the ozone generators. The parameters measured include amperage, voltage, power, and frequency, if this is a controllable variable.

• Flow rate and temperature of the cooling water to all water-cooled ozone generators. Reliable cooling is important to maintain constant ozone production and to protect the dielectrics in the generation equipment.

• There should be a means to monitor the several cycles of the desiccant drier,

Analytical measurements of ozone concentrations must be made in the ozonized gas from the ozone generator, the contactor off-gases, and the residual ozone level in the ozonized water. Methods of ozone measurement commonly used are the: simple "sniff" test, Draeger-type detector tube, wet chemistry potassium iodide method, amperometric-type instruments, gas-phase chemiluminescence, and ultraviolet radiation adsorption. The use of control systems based on these measurements varies considerably. The key to successful operation is an accurate and reliable residual ozone analyzer. Continuous residual ozone monitoring equipment may be successfully applied to water that has already received a high level of treatment. However, a more cautious approach must be taken with the application of continuous residual ozone monitoring equipment for water that has only received chemical clarification because the ozone demand has not yet been satisfied and the residual is not as stable. Ozone production must be closely controlled because excess ozone cannot be stored. Changes in process demand must be responded to rapidly. Ozone production is costly; underozonation may produce undesired effects and overozonation may require additional costs where off-gas destruction is used.

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