For water bottlers, ozone is a good combination of sanitizer and disinfectant.

Ozone can treat water in the following ways:
- It oxidizes both organic and inorganic substances.
- It removes unwanted taste, odor and color.
- It is efficient as a bacteriacide, fungicide and virucide.
- It oxidizes and removes heavy metals.
- It will sterilize the air in the bottles as they fill with water.

Another benefit to ozone is that it will not lead to the formation of trihalomethanes (THMs), which are formed when chlorine is added to raw water containing humic materials. Once a THM is formed, it is difficult to oxidize, even with ozone.

In addition, ozone is generated on-site so chemical storage is not required, and the equipment is easily integrated into the bottling process.

According to the International Bottled Water Association Model Code, ozonation is one of the methods that should be used for bottled water for effective germicidal treatment. 

Ozonation is also one method that the Model Code recommends for treating water that originates from a source not protected from surface contamination. This is to remove or destroy Giardia Lamblia and Cryptosporidium cysts.

Determining ozone demand

Since the chemical composition and purity of water varies so dramatically from region to region and from source to source, the ozone demand can be vastly different for water bottlers. 

For example, natural water - spring, well or artesian well water that has not been treated by reverse osmosis (RO), distillation or deionization - will have a greater ozone demand and will require a higher dosage rate to meet the recommended minimum .2 parts per million (ppm) residual.

In contrast, the ozone demand for drinking or purified water is considerably less because this type of water normally comes from public sources and has been processed by RO, distillation or deionization. These waters have usually been softened to remove "hard" minerals - such as calcium and magnesium - prior to distillation or RO. 

The result is a very high quality water with mineral content at or below 10 milligrams per liter (mg/L). It is the absence of dissolved solid or mineral content that significantly reduces ozone demand. If not properly stored, waters of this purity are subject to rapid bacterial growth. 

A small residual of ozone applied to stored drinking water will maintain water purity without adding chemicals which can adversely affect taste and odor.

Contact methods crucial

Ozone is normally produced at a positive pressure, zero to 15 pounds per square inch (psi), for contacting purposes. Contacting of the ozone gas into the water is a very crucial element in designing an efficient ozonation system. The objective is to get as much of the ozone gas as possible dissolved into the water. 

One problem in using ozone for disinfecting water to be bottled is that its half life - the time it takes to become oxygen again - can last only a few minutes when introduced to some natural waters and as long as 6 to 8 hours in higher purity drinking water.

Because of ozone's characteristically short half life, the process of efficiently dissolving ozone in the water and then allowing it to contact the water for a period of time is critical. 

Two methods of ozone contacting are generally employed in the water bottling process -- static (also called atmospheric) or closed (also called in-line) systems. 

While both types of systems can serve a broad range of plant sizes, static contacting has historically been used in the majority of automated bottling plants. Closed-ozone contacting systems are gaining popularity with smaller, lower volume facilities.

The two methods of ozone contacting work this way:

- A static or atmospheric system. This can be used by bottlers with their own pressurization system and for ozone amounts ranging from 2 grams per hour to several pounds to be delivered at 10 to 30 pounds per square inch (psi).

Ozone is introduced from the bottom of large stainless steel contact vessels through ceramic diffusers - sometimes called air spargers. Depending on the size of the application, the contact vessels are usually between 8 and 18 feet in height and 10 inches to 4 feet in diameter. The water is contacted as it descends through the ozone bubbles rising from the ceramic diffusers.

The critical element in this type of system is the size of the bubbles produced by the diffusers, which must remain small - usually from

100 to 300 microns. Mass transfer efficiencies are directly linked to bubble diameter and the height of the contact vessel. 

Also, periodic cleaning of the diffuser is required as oxidized contaminants will precipitate on diffuser surfaces. Since natural water has not been treated by RO, distillation or deionization, the need for diffuser cleaning is even more important in plants producing natural water products than in purified drinking water facilities.

Atmospheric tanks also require a level control system interfaced with a storage transfer pump. A second pump is also necessary to pressurize the entire bottling system. This arrangement is especially easy to integrate into package bottling plants as they normally have an existing pressurization system.

As a safety precaution, these contact vessels should either be vented to atmosphere or to some type of ozone destruct device if it has not been vented well away from any possible human exposure.

- Closed or on-line contactor. This process uses a pressure/ delivery pump, a baffled or multiple pass contactor and a venturi-type ozone injector. These systems are inherently safer than most contactors because they use vacuum type ozone generators and closed contactors. 

Ozonators that operate on vacuum do not allow ozone gas to escape should a delivery line leak or break. Also, since the ozone injection is controlled by the pump and venturi injector, these systems are very simple.

In closed contactor systems, the pressure/delivery/pump draws water from the storage vessel then pushes it through the ozone injector and contactor, pressurizing the bottler. A small vessel made of stainless steel or a composite material will help by providing pressure sensing for pump pressure control.

The increased mass transfer efficiency provided by the venturi injector - up to 98 percent under ideal conditions - combined with the closed nature of the contactor allows for more precise ozone dosing and reduces the volume requirements of the contactor. 

The ozone gas actually becomes a part of the water solution at the venturi, traveling through the contactor without exposure to air or atmospheric pressure. This adds to the efficiency of the system by allowing for greater ozone saturation. An automatic, stainless steel vent controls the contactor ozone off gas, which is directed to atmosphere or to an ozone destruct unit.

Ozone plays an important role in the water bottling process industry. Properly dosed and efficiently applied, ozone effectively sanitizes and disinfects both natural and treated drinking waters. Combined with other filtration or treatment processes, ozone adds to product longevity by providing bacteria control, bottle sterilization and oxidation of unwanted oxidizable contaminates. 

Ted Rich is director of sales and marketing for ClearWater Tech, Inc., San Luis Obispo, CA.