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Ozone is a popular method for disinfection of spring water prior to bottling. Ozone is a powerful oxidant and will react quickly with bacteria, virus and cysts at low ozone concentration. When employed in a multiple barrier approach, pre-treatments such as cartridge or membrane filtration and UV disinfection followed by ozonation will achieve disinfection of water whilst adding a small residual of ozone to overcome any hygienic inadequacies at the filler and in the bottle itself. Decay studies have shown that ozone residual can be maintained in PET bottle for hours to days, thereby achieving CT and preventing bacterial regrowth.

The primary disinfection by-product of ozone is oxygen which is not harmful to health. Ozonation does not add any other chemicals to the water or cause increase in TDS. Ozone does react with organic and inorganic compounds to form by-products which are not desired but may not be significant, depending upon the concentration formed. The main by-products are as follows:

Bromide ion reacts with ozone to form bromate ion which is deemed to be harmful to health, with the aim to maintain bromate concentration below 10 ppb.

Manganese will react with ozone to form Manganese Dioxide which is a black precipitate. Further ozonation will form permanganate which will impart a pink color to the water.

Iron will react with ozone to form Iron Oxide/Hydroxide which is a brown precipitate

Aliphatic compounds will react with ozone to form aldehydes and carboxylic acids which may or may not be significant depending upon the original organic compound concentration.

Ozone is only sparingly soluble in water and since it is a gas, it follows Henry’s Law. The concentration of dissolved ozone is proportional to the partial pressure of ozone in the air above the water.

Ozone is usually generated using corona discharge of either air or oxygen. Generation from dry (dewpoint < -60 deg.C) air can produce ozone in air a up to 20 g/m³. Generation from either pure (99%) or PSA generated (90-95% in nitrogen) can produce up to 150 g/m³. Higher gas concentration leads to higher dissolved residual.

Dissolving of ozone gas in water is usually accomplished with either a venturi or static mixer . Both venturi and static mixer require minimum flow and pressure to create the energy necessary to dissolve the ozone. This flow and pressure can be provided by a pump. Mass transfer greater than 90% can be obtained with both venturi and mixer.

The positive pressure reaction vessel is more efficient for dissolving ozone and preventing loss of residual than an open atmpospheric tank. Water is ozonated as it enters the vessel and ozonated water flows through the vessel, allowing time for reaction and removal of undissolved air.

Not all ozone dissolves in the water so the excess will exit the top of the reaction vessel. This ozone is usually destroyed so it does not accumulate in areas where operators are working. Ozone gas reacts with activated carbon to form carbon dioxide which can be safely discharged. One disadvantage of carbon is its ability to be a bacterial growth medium. Catalytic media is available which will convert ozone to oxygen in around 1s contact time. The advantage of the catalytic media is that it is not consumed in the reaction.

Modern systems require ozone residual to be controlled to low concentration (0.1 – 0.2 ppm) and within tight tolerances (+/- 0.05 ppm) to minimize bromate formation. It is rare for bottling flow to be steady state with ramp-ups and ramp-downs, slowing and stoppages due to filler, capper or labeler problems. Therefore, the ozone contact and residual control system must be able to cope with all flow scenarios and produce water which conforms to the desired residual specification. To achieve this, a combination of plug flow and CSTR (Continuous Stirred Tank Reactor) must be employed with PID control from the ozone analyzer and perhaps the addition of flow feed-forward.

Ozone residual analyzers must be installed to ensure accuracy and repeatability under all all flow conditions. Amperometric ozone sensors which use membranes and electrolyte are the most common. These sensors require calibration using a photometer. Note: the accuracy of photometer measurement is not greater than +/- 0.03 ppm.

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  O3Pure ozone systems bottled water (515.5 KiB)