1. False. Ozone has been used in Europe to treat drinking water and swimming pool waters for taste and odor control and disinfection since 1906.
2. False. Ozone is a rapidly acting and thorough disinfectant. However, it also dissipates rapidly having a half-life in water on the order of minutes. Ozone can be effectively used as a primary water disinfectant, but in municipal water treatment, ozone is typically followed by small amounts of a chlorine compound for residual purposes. Much of the water’s chlorine demand is satisfied by the ozonation step.
3. True. Ozone is a very powerful oxidant, and is very effective as a prefiltration step in the reduction of iron, manganese, sulfides, organically-bound heavy metals, color, taste and odor organics, turbidity and trihalomethane precursors.
4. False. By drying the air feed gas to at least -30° C dew point, the production rate of corrosive nitrogen oxides can be minimized and the production rate of ozone maximized. Ten to 100 times higher ozone concentrations can be produced by corona discharge generators. The corona discharge production rate is more constant and uses 1/5 or less of the electrical energy than that of UV radiation ozone generators.
5. a, b and c. The higher the concentration of ozone in the gas bubble, the finer the bubble and the longer the bubble is in contact with the water are all critical to increasing the amount of ozone transferred to the water.
6. c. French public health scientists demonstrated that 99.9 percent inactivation of Poliovirus Type I, II and III occurred by exposure to 0.4 milligrams per liter of ozone in water for four minutes, or a Ct value of 1.6. Bacteria are more rapidly destroyed by ozone than viruses. An ozone Ct value of 1.6 can also provide 3 log inactivation of Giardia cysts if water temperature is about 50º F; at colder water temperature ozone Ct requirements can increase to 2.9 for Giardia cyst inactivation.
7. True. The partial oxidation of some organic compounds by ozonation can produce complex materials with cations such as calcium, magnesium, iron, aluminum and manganese. These materials become insoluble and form microflocs. When such microfloculation and increased turbidity occurs, ozonation needs to be followed by filtration.
8. False. Halogenated organic compounds, such as trihalomethanes, are generally much more resistant to oxidation, even by ozone, than are the precursor, nonhalogenated organics. Removal of THMs in drinking water ozonation treatment is due mostly to the physical air stripping of the volatile THMs by the aerating action of the ozone/air mixture bubbling through the water.
9. b. An Oxidation-Reduction Potential (ORP) meter or monitor/controller can be used to continuously measure the potential of the water to oxidize contaminants in the water. A minimum ORP level of 700 millivolts can ensure disinfected water. A two-electrode ORP monitor can be used to automatically call for more ozone feed and to shut off ozone feed when levels are respectively low or high, thereby maintaining the water bacteria-free.
10. a, b and c.
