» 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
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
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
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 specifications.
- 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 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 applied.
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
- 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 a
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 micro-organisms.
- 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
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
||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; Vinclozolin
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
- 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 effects.
- Removes color, taste, odor and Aids coagulation.