» Ozone in Drinking Water
Ozone in Drinking Water
When ozone is applied, as a gas, for drinking
water treatment, it is done primarily because of its excellent oxidative
strength. This powerful oxidation potential allows ozone to be effective
in the reduction or elimination of color, after taste and odor, all of
which may be fundamental problems associated with a specific water
supply. More importantly, ozone will effectively destroy bacteria and
inactivate viruses more rapidly than any other disinfectant chemical.
Ozone is also very effective in oxidizing heavy metals. Iron and
manganese can be reduced to very low, safe levels in water supplies
through ozone oxidation. When properly applied at the start of a water
treatment process, ozone will not lead to the formation of halogenated
compounds such as Trihalomethanes (THM's) which are formed when chlorine
is added to the raw water.
The Main Effects of Ozonisation of Drinking Water
- Iron and Manganese Removal : - The standard
oxidation-reduction potential and reaction rate of ozone is such
that it can readily oxidize iron and manganese present in the raw
water and in water with low organic content.
While Iron and Manganese don't pose health problems, but water
contaminated by iron and manganese can stain water fixtures and
clothing that is washed with this water. Chlorine can also be used
for oxidation of iron and manganese, but significantly more chlorine
is required versus ozone. This is due to the fact that ozone has an
oxidation potential 150 times greater than chlorine. The use of
chlorine can also result in the formation of THM's if organic
material is present in the water.
Ozone oxidizes Iron from Fe (II) to Fe (III). Fe (III) hydrolyzes
to Fe (OH3) which precipitates to a solid form which can be
filtered. The oxidation reaction requires 0.43 mg of ozone per mg of
Fe (II). Excess ozone can be used without negative effect. Fe
oxidizes in the pH range of 6-9. Ozone oxidizes Mn (II) to MnO2 (Mn
IV) which is insoluble and can be filtered out of water. The
oxidation reaction requires 0.88 mg of ozone per mg of Mn (II).
Excess ozone beyond this ratio will form soluble Mn (VII),
permanganate. If oxidizable organic material is present in the water
and there is sufficient contact time, permanganate will be reduced
back to MnO2 (Mn IV). Manganese oxidation is most effective around a
pH of 8. In general, when organic materials are present in water,
more ozone will be required than the amount shown above since ozone
will also oxidize these materials.
- Color Removal : - Water appears colored when visible
radiation is absorbed by dissolved materials or when light is
reflected by suspended solids. Colored water is basically found at
dye houses, textile concerns, food and beverage processors,
slaughter houses and other industrial plants. Many industries have
already started using ozone, which is a more powerful and a safer
substitute than chlorine for color removal.
The best results are achieved when water has been treated to lower
BOD, COD and suspended solids (SS) values so that the ozone reaction
is primarily for color removal. Wastewater is Ozonated after it
exists from chemical or/and biological pretreatment at a dosage from
50 mg/lit to 150 mg/lit. At these levels, color can be reduced by 90
to 98%. The dosage simultaneously reduces chemical oxygen demand
(COD) by about 45%. (Small increases of BOD, 5 to 9%, may occur.)
Color removal efficiency depends on the ozone dosage, the feed's
color values, the wastewater type and temperature and water
characteristics. Temperature less than 30oC produce the optimum
conditions for ozone solubility. Ozone installations for this
application represent a significant capital cost, but offer lower
operating expense than conventional treatment using chemical
coagulants. In addition to the cost of chemical, the coagulant
process generates sludge that requires disposal and further
expenditure. Generally, the investment for an ozone installation can
be paid back in 3 to 5 years, depending upon the size and other
- Taste and Odor Removal : - Odor and taste in drinking
water can be due to have several reasons. Odor and taste forming
compounds can be present in raw water, but they can also be formed
during water treatment. These compounds may derive from the
decomposition of plant matter, but normally they are a result of the
activity of living organisms present in the water. Inorganic
compounds such as iron, copper and zinc can also generate some
taste. Another possibility is that the chemical oxidation (chlorine
treatment) leads to unpleasant taste and odor.
Odor and taste forming compounds are often very resistant. This
causes elimination to be a very intensive process. For the
elimination of taste and odor, several processes can be appropriate
such as oxidation, aeration, granular active carbon (GAC) filtration
or sand filtration. Usually, a combination of these techniques is
Ozone can oxidize compounds in a range of 20-90% (dependent on the
type of compound). Ozone is more effective for the oxidation of
unsaturated compounds. As was the case for the oxidation of
pesticides, ozone combined with hydrogen peroxide (AOP Process) is
more effective than ozone alone. Geosmin and 2-methyllisoborneol
(MIB) are examples of resistant odorous compounds, which are often
present in the water. These are produced by algae and have low odor
and taste threshold. Nevertheless, ozone removes these compounds
very effectively.Generally, the most effective way to remove taste
and odor components appears to be a combination of pre-oxidation and
filtration, but ozone with sand filtration and GAC filtration is the
most efficient combination (upto 92% removal).
- Removal of Organic and Inorganic Matter : - All water
resources contain natural organic matters (NOM). Concentrations
(usually measured as dissolved organic carbon, DOC) differ from 0.2
to more than 10 mg. NOM creates direct problems, such as odor and
taste in water, but also indirect problems such as organic
disinfection byproduct formation, support of bacterial regrowth in
the distribution system, etc. To produce pure drinking water, the
removal of NOM is a prior task in modern water treatment.
Ozone, like any other oxidant, seldom achieves a complete
mineralization of NOM. Organic matter is partly oxidized and
becoming more easily biodegradable. This result in a higher amount
of BDOC (Biodegradable DOC), As a result ozone improves the removal
process of NOM by a subsequent filter, when it is used as a
pre-oxidant. In a research, the effect of ozone in combination with
a biological filter is described. The combined treatment resulted in
a reduction of DOC by 40-60%. The removal is even greater when ozone
is used in combination with a coagulant. This is because ozone can
enhance the coagulation process. The combination
coagulation-ozone-bio filtration results in a DOC reduction by 64%.
When only bio filtration was applied, the reduction rate was only
13%. The optimal concentration to remove organic matter by ozone was
at an ozone dose of O3/DOC = 1 mg/mg.
Most inorganic matters can be eliminated by ozone quite fast. After
Ozonation, bio filtration is also required for inorganic matter.
Namely, oxidation forms unsoluble compounds that need to be removed
during the next water purification stage.
- Removal of Disinfection By-Products : - Disinfection
byproducts (DBP) are mainly formed during the reaction between
organic material and a disinfectant. The reaction of chlorine with
matter can lead to the formation of chlorinated organic DBP's, such
as Trihalomethanes (THM). Ozone can also react with organic matter
and form DBP's. These are mainly organic disinfection byproducts,
such as aldehydes and ketones, which can be easily degraded in a bio
filter (90-100%). Generally, this organic ozone DBP's do not form
risk of violation of drinking water standards, when ozone is used as
To reduce the amount of DBP's at a conventional disinfection system
(disinfection by chlorine) it is important that potential to form
DBP's remains low. This is often expressed as DBP formation
potential (DBPFP). The potential to form DBP's can be reduced by the
removal of (most of the) NOM, for example by pre-oxidation with
ozone (ozone-filtration). This combination can lower the DBPFP by
70-80% when chlorine is used as a final disinfectant. This concerns
the DBPFP for THM's, HAA (haloacetic acids) and chloral hydrate.
Ozone is a more effective disinfectant than chlorine, chloramines
and even chlorine dioxide. An ozone dose of 0.4 mg for 4 minutes is
usually effective for pre-tested water. Several studies proved that
ozone, unlike chlorine products, can deactivate resistant
- Removal of Pesticides : - Micro-pollutants such as
pesticides may occur in surface water, but also increasingly in
groundwater. Drinking water standards for pesticides in the European
Union are strict.
Several surveys show that ozone can be very effective for the
oxidation of several pesticides. It is proved that three barriers
(storage-ozonation-granular active carbon filter) are effective and
safe enough for the removal of pesticides. From 23 tested
pesticides, 90% were degraded sufficiently (80% degradation). For
highly resistant pesticides, a higher dosage of ozone is advised, or
ozone combined with hydrogen peroxide.
||pH 7.2; 5°C; O3/DOC = 1.0
||pH 7.2; 20°C; O3/DOC = 1.0
||PH 8.3; 20°C; O3/DOC = 1.0
|Chlortoluron; Isoproturon; Metoxuron;
Advantages Of Using Ozone For Drinking Water
- Possesses strong oxidizing power and requires short reaction
time, which enables the germs including viruses, to be killed within
a few seconds
- Produces no taste and odor.
- Increases the Oxygen content in the water after disinfecting.
- Requires no additional chemicals.
- Oxidizes Iron and manganese.
- Destroys and removes algae
- Reacts with and removes all organic matter.
- Decays rapidly in water, avoiding any undesirable residual
- Removes color, taste, odor and Aids coagulation.