By Rick Hess

Summary: Bottled water applications present their own problems in regard to disinfection as well as operation. Though considered the most effective technology for disinfecting bottled water, ozone isn’t free from its share of challenges. One main factor for bottlers to consider is the contacting process between water and ozone. Ultimately each bottler will have to make choices based on their individual needs.

Ozone is the primary disinfectant of choice for bottled water. Easily 95 percent of bottled water plants use it in some capacity. Ozone is effective in bacteria, virus and protozoa inactivation, as well as sanitizing bottles when washing prior to filling. Almost no other water treatment technology is as effective as ozone in reducing various pathogens.

Still, each technology has advantages and disadvantages. For bottlers using ozone, bromate formation is the overriding issue. This article will discuss possible ways that ozone control can be achieved to mitigate the conversion in source waters that may contain the organic bromide ion.

The problem is that presence of this ion may be inconsistent, which offers particular challenges for monitoring and control equipment designed to reduce potential resulting bromate formation. Understanding these factors and such instrumentation will be imperative to maintain, ozone as an effective tool in bottlers’ water treatment tool chest.

More not necessarily better
There are four primary factors in determining the amount of bromate that can be formed in any water. They are bromide concentration, ozone dose, pH and temperature. Bottlers that produce natural spring waters must contend with the last three factors in controlling bromate. Of these, the most important factor is the ozone dose. In the past, many bottlers believed that if some ozone was good for disinfection, then more was better. Today, bottlers must control the amount of ozone in the product or run the risk of creating bromate levels that exceed the 10 parts per billion (ppb) standard set by the Food and Drug Administration.

Meeting the challenge
Controlling the ozone residual is challenging while producing a high quality product like bottled water. There are several ozone generators that produce ozone consistently and reliably. The issue of bromate control is primarily in the contacting of ozone and water, not in the generation of ozone. Most current ozone generators can adjust their outputs quickly through a variety of controls. Still, ozone contractors for bottled water have challenges not faced by other applications.

Municipal water, swimming pools and cooling towers all operate on a continuous basis; bottled water and other beverage production process don’t. Five-gallon bottle fillers cycle as each group of bottles enter and exit the filler. Small package fillers (0.5-1.5 liters) stop and start whenever bottles jam, caps misfeed or boxes hang up. Plus, there are operator breaks and lunch periods to consider. Unless the ozone contacting system is designed to account for these stoppages, th eozone residual will fluctuate every time the filler stops and restarts.

Fine bubble diffusion tanks do a good job of ozone contacting, but many only control the flow of water. When the tank reaches its optimum level, water stops flowing but ozone continues to build a residual that’s greater than the bottler requires. Another problem occurs when one contractor is used for two or more filling lines. As each filler starts and stops, the flow of water will be altered. If the ozone gas flowing to the contactor isn’t adjusted to be proporational to the water flow, higher or lower residuals will result.

Thinking positively
The best way to contact water with ozone is by positive pressure where the ozone gas pressure is higher than the water pressure. When the water stops and restarts, the pressure of the gas immediately forces the ozone into the water. Control is also enhanced by valves that control water and ozone gas simultaneously. Whenever water stops, ozone must also stop.

The flow of water into the contactor should be metered to 105 percent of the water leaving the contactor. By nearly matching the inflow with outflow, the bottler will get as close to a continuous flow as possible. Ozone should contact water in the piping system before the contact tank. Contacting in the pipe eliminates the possibility of vertical channeling and short-circuiting of the water being treated.

Automatic reaction
The newest development in ozone technology is automatic controls. Auto controls take a signal from an ozone analyzer, through a programmable logic controller (PLC) and to the generator. The generator then adjusts power to increase or decrease the amount of ozone being produced. The controller can automatically start and stop the generator over extended shutdown times like operator breaks and lunches. Bottlers will have the most success in maintaining a uniform ozone residual with the combination of controls on both the ozone generator and ozone contactor.

Of the remaining two factors that reduce bromate formation, pH reduction will have a greater effect. A reduction from a pH of 7 to 6 may reduce the conversion of bromide to bromate by as much as 50 percent. While this reduction is dramatic, it’s difficult to achieve. To reduce pH, bottlers must add carbon dioxide to the product water. This addition must be districtly controlled to achieve the pH reduction and avoid taste problems.

The last factor, temperature, will have the least effect on bromate conversion but may still be a useful method of addressing the problem. Waters with high temperatures combined with ozone will convert more bromide to bromate. Higher temperatures make ozone more active, which increases the conversion. By lowering the temperature of the water, the ozone will become less reactive and less bromate will be formed. While temperature reduction may be beneficial for bromate reduction, temperature reduction will also reduce the disinfection rate of ozone. Bottlers are forced to balance these two conflicting results to achieve designed outcomes.

Bromate reduction is a difficult challenge for water bottlers to achieve. Each type of water is different. Each bottling plant is different. Certainly, there’s no single answer for bottlers, One size doesn’t fit all. Different applications will require different contacting and are best approached on an individual basis by people knowledgeable in water bottling.

About the author
Rick Hess is president of Hess Machine International, of Ephrata, PA, and was president of Ephrata Diamond Spring Water Co. before selling that to McKessan manufactures ozone water disinfection systems for the international bottled water industry. Hess also has been president of the International Bottled Water Association and Pennsylvania Bottled Water Association, and serves on the board of the International Ozone Association. He holds a bachelor’s degree in business administration from Robert Morris Collge. He can be reached at (717) 733-0005 or email: [email protected].


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