By John Swancarra
Ozone treatment of bottled water has been used in the industry for over 30 years. Ozonation of the product water provides an efficient, safe method of disinfecting the water against water-borne microorganisms or other bacteria that may be present in the final water, the bottling equipment, and the final filled bottles and caps. It also contributes to good tasting water.
It is very important, however, that the ozone by injected into the water carefully and precisely for maximum effectiveness.
What Does Ozone Do?
An unstable and colorless gas, ozone (O3)is a powerful oxidizer and a very effective germicide. In fact, ozone is a more effective disinfectant than chlorine.
Shortly after ozone is generated, it breaks apart and returns to its natural form of oxygen. As this process occurs, the free atom of oxygen seeks out any foreign particles in the water and is attracted to them. This action creates an environment where bacteria and other organic matter virtually disintegrate when they come in contact with this free oxygen molecule, protecting water from waterborne bacterial contamination.
The variables determining the effectiveness of ozone in killing bacteria are contact time and residual ozone concentration achieved in the product water. This ozone concentration
residual is first dependent on how much ozone is injected into the product water and then the amount of ozone demand in the water.
Ozone treatment provides longer store shelf life without unfavorable tastes and odors associated with untreated waters or waters treated with chlorine.
Ozone must be injected correctly to be safe and effective. Over-ozonation of the water, for example, may lead to taste problems due to a high level of ozone (0.40 ppm or more) and reactions with the plastic in the plant piping, and even with the bottle itself. Sometimes, in the non-returnable market, too much ozone or improperly injected ozone may allow some ozone to outgas into the air layer between the water and the cap. If this bottle is opened soon after bottling, the consumer may notice a metallic taste in the water caused by the ozone smell.
The presence of bromide in some treated waters, especially spring water or well water, has become a major concern in recent years. Bromate, a suspected carcinogen in levels as low as 10 ppb, is formed by oxidation of the bromide ion during the ozone disinfections process.
Additionally, final product water purified by reverse osmosis (RO) causes some problems with ozonation levels if the RO water still contains TriHaloMethanes (THMs). THMs are byproducts in municipal waters caused by the chlorination process and cannot be removed by the RO process. Ozone treatment will oxidize and remove the THMs, but this will use up the ozone and lower the residual levels of ozone in the final product water. Testing for THMs in the feed water and removal by carbon filtration before or after the RO will prevent the problem and eliminate the need for a larger ozone system.
Many, if not all, of these benefits and drawbacks associated with ozonation are directly related to the quality of the ozonation equipment and the ozonation method used.
The Ozonation Process
The bottled water industry uses several methods of introducing ozone into the final product water before bottling. In general, the three main methods used are inline atmospheric contacting, batch processing, and inline pressure contacting. Each type has its benefits and weaknesses. Choosing the right method can prevent many problems that could arise. (The following method titles are the author’s descriptions and are not an “official” industry designation.)
This ozonation method involves drawing the product water out of the storage tanks with a pump and delivering the water to a large atmospheric stainless steel contact tank. Then, the water is either ozonated by Venturi injection assembly inline with the water flow, or by ozone bubbling into the contact tank with a diffusion stone. In the contact tank, the water requires a specified length of “contact time” with the ozone to be treated effectively, and is then delivered directly to the bottle filler by another pump. This process is considered “real time” in that, as soon as the contact tank fills and both pumps are delivering water at the same flow rate, the bottle filler can operate continuously without waiting for the right ozone level to be achieved.
Many large bottled water companies currently use this form of ozonation. Having the appropriately sized contact tank is very important, especially if the ozone is bubbled into the tank. This process may also require considerable fine-tuning to balance the pumps. This system generally requires an ozone monitor/controller unit to insure proper ozone levels.
The batch processing method starts by ozonating a large storage tank until the desired ozone level is reached. Two possible methods of storage tank ozonation include (1) “Circulation” using a small circulating pump, a small ozone generator and a Venturi injector to create and entrain the ozone gas into the water stream circulating into the tank;
or by (2) “Bubbling” using a small ozone generator and air pump to create the ozone gas and push the ozone gas through a diffusion stone into the storage tank.
When the desired ozone level is reached, a separate pump delivers the ozonated water from the storage tank to the filling operation. The tank is ozonated continually by whichever batch processing method is used to maintain an acceptable ozone level. Batch processing is usually good for small bottling operations that do not require large amounts of processed water.
Inline Pressure Contacting
The first method uses one pump to deliver the water from the storage tanks through a venturi injection assembly with a large amount of bypass into a pressurized contact tank, then out to the bottle filler. This requires a return line back form the filler to the storage tanks. This technique is ideal for small bottling operations and for small fillers that do not require high pressures to fill. If sized correctly, an ozone monitor/controller may not be needed.
The second method uses two pumps: a main pump to draw the product water out of the storage tanks and to push the water through the contact tank and into the filler; and a smaller pump to boost some of this pressurized water through a venturi injector assembly to draw the correct amount of ozone into the water stream. The two streams of water merge and mix together in the pressurized contact tank on their way to the filler. This method is also called “side-stream” ozonation. If sized correctly, an ozone monitor/controller may not be needed; however, it is best to have one to ensure that the
correct level of ozone is supplied to the filler. This is a good method for intermediate-sized bottling operations.
Recommended Ozone Equipment and Method
The most important factor in the ozonation process is the equipment and the method used to introduce ozone into the water. Equipment, such as the following, is recommended to create ozone and to inject the ozone into the product water:
A good pressure swing adsorption system is highly recommended. This equipment removes nitrogen from the air stream and delivers a 90%-plus dry oxygen stream to the ozone generator for higher ozone concentrations..
A good high-frequency Corona Discharge unit is recommended. These units are capable of producing ozone concentrations in the air stream of from 4% to 6% by weight. The ozone is created as the oxygen stream travels through the ozone generator’s corona discharge dielectric cell. The proper electrical charge with the right frequency will create a high-quality ozone concentration. Some equipment manufacturers do not rate their generators accurately. Unfortunately, there are no real ozone unit industry standards that can be reliably used to judge unit output.
A good, properly sized Venturi-type injector is absolutely necessary to ensure the formation of small micro-sized bubbles as the ozonated stream of air is sucked into the product water stream. A well-designed assembly is capable of entraining the ozone into the water with an efficiency of 95% or better.
A properly sized contact tank is necessary to allow more gas into the solution, permit adequate contact time for the water with the ozone to oxidize contaminants, or disinfect the water and release any excess gas that did not go into the solution.
Ozone treatment is an effective disinfectant for water being used in bottled water operations. The process requires careful, precise operation and quality equipment to ensure the bottled water is properly disinfected and tastes good through out its shelf life. The best system for introducing ozone into the final bottled water product depends on many factors: the size of the operation; the type of water to be treated; the level of ozone required; and the current or proposed bottling equipment. To get the best quality ozonated bottled water, it is best to consult a company that deals with complete bottled water plant systems and that supplies complete integrated systems.
About the author:
John Swancarra is an engineer with Norland International, Inc. He has worked in the bottled water industry for over 20 years.