How Ozone is Produced

In the same way that ozone is formed naturally by the discharge of electricity during a thunderstorm, large quantities of ozone are produced commercially in the modern electrical ozone generator.

The passage of a high voltage, alternating electric discharge through a gas stream containing oxygen will result in the breakdown of the molecular oxygen, to atomic oxygen. Some of the atoms of oxygen thus liberated can reform into ozone, while others simply recombine to again form oxygen. In order to control the electrical discharge, and maintain a "corona" or silent discharge in the gas space and avoiding as much as possible, arcing, a dielectric space or discharge gap is formed, using a dielectric material such as glass or ceramic. A ground electrode, constructed usually in 316L stainless steel (a material which has demonstrated high resistance to ozone oxidant) serves as the other boundary to the discharge space. This can be accomplished in many ways, but the most frequently employed geometry is that of the cylindrical dielectric (or Siemens Type) ozone generator. The cylindrical dielectric is more space efficient than other shaped and consequently more economical.

Ozone produced commercially for oxidation reactions is always produced as a gas, from air at concentrations between 1.5 and 2.0 percent by weight in air, or from oxygen at concentrations greater than 6% and up to 12% by weight. Since ozone is highly reactive, and has a short half life, it is very difficult to store and transport. Consequently ozone is always generated on site for immediate use.

Typical Applications

Drinking Water Treatment

When ozone is applied, as a gas, for drinking water treatment, it is done primarily because of its oxidative strength. This powerful oxidation potential allows ozone to be effective in the reduction or elimination of color, taste and odor, all of which may be fundamental problems associated with a specific water supply. More importantly, ozone will effectively destroy bacteria and inactivate virus more rapidly than any other disinfectant chemical. Ozone is also used to oxidize heavy metals. Iron and manganese can be reduced to very low, safe levels in water supplies through ozone oxidation. This same process is used to liberate organically bound heavy metals, which are otherwise not easily removed.

Ozone, properly applied at the start of a water treatment process, will not lead to the formation of halogenated compounds such as Trihalomethanes (THM's) which are formed when chlorine is added to the raw water containing humic materials. Once a THM is formed, it is quite difficult, if not impossible to oxidize, even with ozone. Thus, ozone can be used as an oxidant, where it is applied at the latter stages of water treatment. Whatever ozone gas is not consumed during the treatment of drinking water is collected and converted back to oxygen through ozone off-gas destructors, before release to the atmosphere.

There are more than two thousand installations worldwide which use ozone to treat drinking water. In Canada, there are over sixty water treatment plants which use ozone in some capacity.

Up until 1986, ozone had been installed in no more than 25 water treatment plants in the United States. With the promulgation of the United States Environmental Protection Agency (US EPA) Safe Drinking Water Regulations (SWTR) of 1986, the use of ozone in the treatment of drinking water in the USA has increased dramatically. There are presently more than two hundred and fifty ozone treatment plants under design or construction in the United States. In the next five years many hundreds of larger municipalities will be adding ozone to their water treatment plants.

As water treatment plants respond to US EPA regulations more than 10,000 smaller drinking water treatment facilities will be looking to add ozone oxidation processes to their drinking water treatment.

Ultrapure Water

The use of ozone in the printed and integrated circuit board industry for the production of ultrapure water is a well documented application. Ozone is also applied to the deionized water that is used to wash substrates during the production of printed circuit boards.

Malodorous Air Treatment

The application of ozone or ozone in combination with other chemicals for the treatment of malodorous air has a long history of success. Typically, in wastewater treatment plants, foul air can be collected and treated with ozone to reduce the odor. Ozone is usually applied in combination with wet scrubbing equipment.

Pulp and Paper Wastewater Treatment

As general negative reaction to the dispersion of waste effluents containing chlorinated disinfection by-products grows, the consideration of the use of ozone in the many phases of the pulping process grows. It should be pointed out that the pulp and paper industry has been examining the use of ozone for many years. Ozone can be applied as a final polishing treatment to the waste effluent from the plant. Ozone is also applicable in the bleaching process and, similar to wastewater plant foul air deodorization, can be applied to the odor which emanates from the process.

Wastewater Treatment

The treatment of wastewater with ozone, again primarily for disinfection or at least log level of bacterial reduction, was a key focus of its use in the United States during the late 1970's and early 1980's. More than twenty plants were installed, in various locations with various design consideration. The key reason for the use of ozone was however disinfection. This approach is again being considered in light of the desire to avoid chlorination.

Fish Hatcheries

Using ozone instead of chlorine has some significant advantages. First, the ozone carrier gas will increase the dissolved oxygen level in the fish tanks. Second, the fish will not be exposed to the by-products of chlorination with all the ramifications that are entailed. Dosage rates for fish hatcheries are typically in the same order of magnitude as for low level water treatment.