The Water Quality Assn. (WQA), a founding member of the European Drinking Water (EDW...
Ozone treatment is one of the most effective microbiological
barriers that water bottlers can employ to protect consumers against
microorganisms. Consumers are largely unaware, however, that many bottlers
worldwide rely on ozone to provide a safe and good tasting product. Since the
1970s, ozone has played a critical role in helping the bottled water industry
deliver a safe and aesthetically pleasing product. In fact, one could say that
ozone saved the bottled water industry in its infancy, when bottled water
wasn't always properly disinfected and was frequently criticized in television
and newspaper investigative reports.
Today, a few bottlers in the United States may face a new
challenge in applying ozone without exceeding the newly established
disinfection byproduct (DBP) maximum contaminant level (MCL) for the bromate
ion. Because of the relative and perceived ease of ozone treatment, many
bottlers still don't use proven ozone process controls and monitoring
technology. Thus, they're yet to assure precise ozone treatment, style="mso-spacerun: yes"> which is necessary when certain
contaminants--such as bromide, from which bromate is formed--are present in the
source water. The careful use of controls can result in bottled water of a
Ozone treatment played a pivotal role early in the bottled
water process that contributed to the healthy growth the industry has enjoyed for
many years. In the early years, not all water bottlers used ozone treatment for
disinfection. In addition, the water bottling process wasn't fully developed,
nor was the bottled water always sealed properly. During the handling and
squeezing of the bottle, air and airborne organisms could enter the product.
Thus, after days or weeks of storage, often on supermarket shelves, the
potential existed for the explosive growth of microorganisms, which could lead
to undesirable taste and odor and health problems. Several well-publicized
bottled water recalls took place during this time.
Shortly thereafter, under pressure from many state health
organizations, disinfection processes for water bottling, with ozone as a key
component, were developed. Required ozone dosages, contact times and closure
requirements for the various types of bottles and waters were established.
Ozone proved to be the magical oxidant that could disinfect everything--the
water, bottling equipment, bottle and sealed cap--and then decompose to
harmless oxygen and disappear without leaving a taste or odor.
Ozone disinfection enabled the water bottler to produce
high-quality, storage-stable bottled water free of byproducts and the taste and
odor associated with the use of chlorine for disinfection and oxidation. These
characteristics and the claims of good-tasting, odor-free, pollution-free,
healthy water led to the rapid growth of the bottled water industry through the
'80s and '90s with overall public consumption growth consistently approaching or
exceeding double-digit rates. (See Tables 1 and 2.)
Ozone (O3) is a gaseous material made from oxygen in an
electric discharge field (corona discharge) type ozone generator. Early ozone
generators operated at 1 to 2 percent weight (% wt.) ozone. Today, the output
of the ozone generator typically contains 3 to 10% wt. of ozone in the
unreacted oxygen feed gas stream. This ozone gas stream is brought into contact
with the water to be treated in a device called an ozone contactor. In the ozone
contactor, the ozone is dissolved in the water and the undissolved ozone in the
off-gas is discharged through an ozone decomposer and released at rooftop
Ozone is a powerful oxidant and an exceptional chemical
disinfectant. The ozone treatment process is an integral part of the drinking
water treatment plant operation in more than 3,000 municipal water
installations worldwide. These plants supply water to the residents of many
major international cities such as London, Paris, Budapest, Kiev, Moscow and
Singapore. In the United States alone there are nearly 400 ozone drinking water
installations including those in Los Angeles, Dallas, Milwaukee, Orlando and
Atlanta, and more are coming to Boston and New York City.
The ozone/water contacting system serves two primary
functions. First, it is used for the dissolution or mass transfer of the ozone
gas from the output gas stream mixture of the ozone generator into the water to
be treated. The balance of the ozone remaining in the off-gas is destroyed by
an ozone decomposer unit so that any off-gas discharged into the atmosphere
contains an ozone concentration less than 0.1 parts per million (ppm)--or
milligrams per liter (mg/L)--of ozone.
Second, the ozone contactor is a reactor. It provides the
reaction time--detention or contact time--to allow the desired disinfection
and/or oxidation processes to occur in the water. Once the ozone is dissolved
in the water it undergoes three simultaneous reactions.
style='font-weight:normal'>. The disinfection treats the water against
bacteria, viruses and parasites such as Giardia and Cryptosporidium. While much
more detail can be given (see FYI sidebar), suffice it to say that ozone is
highly effective against all of the above microorganisms and more.
oxidation. Ozone is a powerful oxidizing
agent and is very effective against essentially all taste- and odor-causing
organic materials and oxidizeable inorganics such as iron, manganese and
sulfide ions. Again, additional details on the specifics of this reaction have
been expanded on in other articles (see FYI sidebar).
style='font-weight:normal'>. Ozone is an unstable material under room
temperature and near room temperature conditions and decomposes to oxygen
fairly quickly. Primarily, water temperature and pH influence the decomposition
rate. The half-life of ozone at 20°C and pH 7.0 in potable tap water
typically is 24 minutes.
The objectives of ozone treatment in water bottling include
of water against all microorganisms that might be present in the water.
of bottles, especially reusable bottles in the wash prior to bottling.
of the wetted parts of the water bottling equipment and machinery.
of the surface of the bottle and the sealed cap of the bottled water.
against the airborne microorganisms that may be present in the air above the
water in the bottle.
Ozone treatment is a unique and valuable process. It can
accomplish all the aforementioned treatment objectives without leaving a taste
or chemical residual behind when accurately applied and controlled. Ozone is an
exceptionally powerful disinfectant and oxidant. It does its job and
disappears. With appropriate pretreatment and careful monitoring and controls,
it can leave water relatively free of disinfection byproducts as well.