Ozone/Hydrogen Peroxide in
Water Treatment Applications
Department of Civil & Environmental Engineering
University of Southern California
Los Angeles, CA 90089-2531
• Reaction Mechanisms
• Comparisons Between Ozone and
O3/H2O2 in Water
• Applications of O3/H2O2 in Water
• Advantages and Disadvantages
• Regulatory Background
• Advanced Oxidation Processes (AOPs)
• About Ozone (O )
• Property and Health Effect of Ozone and H O
• The 1996 Congressional Safe Drinking Water Act
Amendments required the U.S. Environmental
Protection Agency to develop improved drinking
water regulations. The Disinfectants/Disinfection
Byproducts Rule addressed concerns related to
byproducts from the disinfection process.
• The rule called for reduced levels of disinfection
byproducts, including trihalomethanes ( THMs)
which are formed when water high in organic
materials (dissolved, decayed vegetation or peat) and
bromide (a salt originating from seawater) are
treated with chlorine.
• Traditional chlorination water treatment process
with THM byproducts forming potential could not
meet the new standards. The ozone can be used as a
water oxidant/disinfectant to effectively comply with
the new standards and protect drinking water
Advanced Oxidation Processes
• Advanced oxidation processes are defined as those
which involve the generation of hydroxyl radicals in
sufficient quantity to affect water purification.
• The highly reactive hydroxyl free radicals are
produced to oxidize various compounds in water.
Various AOP Systems
• Ozone/Hydroxide Ion (O /OH )3
• Ozone/Hydrogen Peroxide (O /H O )
3 2 2
• UV Radiation/Hydrogen Peroxide (UV/H O ) 2 2
• Ozone/ UV Radiation(O /UV)
• Heterogeneous Catalytic Ozonation (HCO)
• Photocatalysis (UV/TiO )2
About Ozone (O3)
• Ozone is a three-atom form of oxygen whereas
oxygen in air is a two-atom form.
• Ozone is formed when oxygen gas is passed through
an electrical field in a specially designed generator.
A small portion of the oxygen (less than 10%) is
converted to ozone.
• Ozone gas cannot be stored effectively and is
immediately bubbled into the water.
• The ozone process is self-contained, and no ozone is
released into the atmosphere.
• Generating ozone is about four times more costly
than traditional chlorine disinfection, primarily due
to electricity and oxygen needed in the process.
Property and Health Effect
of Ozone and H2O2
• Very low concentrations of ozone can be harmful to
the upper respiratory tract and the lungs. The
severity of injury depends on both by the
concentration of ozone and the duration of exposure.
• Severe and permanent lung injury or death could
result from even a very short-term exposure to
relatively low concentrations
• To protect workers potentially exposed to ozone,
OSHA established a permissible exposure limit
(PEL) of 0.1 ppm, calculated as an 8 hour time
weighted average. Higher concentrations are
especially hazardous and NIOSH has established an
Immediately Dangerous to Life and Health Limit
(IDLH) of 5 ppm.
Property and Health Effect
Hydrogen Peroxide (H2O2)
• HO2 is stored in a cool, dry, well-ventilated area and
away from any flammable or combustible
substances. It should be stored in a opaque container
composed of non-reactive materials because H2O2
breaks down quickly when exposed to light.
• Concentrated H O , if spilled on clothing or other
flammable materials, will preferentially evaporate
water until the concentration reaches sufficient
strength, at which point the material may
• Low concentrations of H O , 3% or less, will
chemically bleach many types of clothing to a
pinkish hue. Caution should be exercised when using
Reactions of Ozone/Hydrogen Peroxide in Water
H 2 O 2 + H 2 O ↔ HO 2 + H 3O + ka = 10−11.6
O 3 + HO 2 ↔ OH ⋅ + O 2 + O 2 k10 = 2.2×106 M −1s −1
O 2 + H + ↔ HO 2 ⋅
1/k2 = 10−4.8
O3 + O 2 ↔ O3 + O 2 k2 = 1.6×109 M −1s −1
k3 = 5.2×1010 M −1s −1
O 3 + H O 2 ↔ HO3 ⋅
− + −
k −3 = 2.3×102 s −1
HO 3 ⋅ ↔ OH ⋅ + O 2 k4 = 1.1×105 s −1
Reactions of O3/H2O2 in Water
HO2− H 2O 2
+ O3 O2
Ozone Decomposition Process by Hydroperoxide Ions
Summary of O3/H2O2 Chemistry
• Hydroxyl radicals (OH·) are produced
during the spontaneous decomposition of
• Addition of hydrogen peroxide increases the
ozone decomposition and produces high
concentrations of hydroxyl radicals (OH·).
Reactions with Other Water Quality Parameters
• pH and bicarbonate alkalinity affect the
O3/H2O2 oxidation effectiveness.
• At high alkalinity, bicarbonate and carbonate
competition for hydroxyl radicals.
• At high pH, carbonate competition for
Oxidation by O3/H2O2 in Water
Oxidation by O3/H2O2 in Two Reactions
• Direct oxidation of compounds by aqueous
ozone [O3 (aq)].
• Oxidation of compounds by hydroxyl
radicals (OH·) produced by ozone
• Free radical oxidation is more effective than
direct oxidation by aqueous ozone.
• The oxidation is more reactive and much
fast in the O3/H2O2 process compared to the
ozone molecular process.
Comparison between Ozone and O3/
H2O2 in Water
PROCESS O3 O3/H2O2
Ozone decomposition rate Normal decomposition Accelerated ozone
Ozone residual 5-10 minute Very short lived due to
Ozone path Usual direct aqueous Primary OH· oxidation
Ability to oxidize Fe and Mg Excellent Less effective
Ability to oxidize taste and Variable Good, OH· more
odor compounds effective than O3
Ability to oxidize chlorinate Poor Good, OH· more
organics effective than O3
Disinfection ability Excellent Good
Ability to detect residual for Good Poor, can not calculate
disinfection monitoring CT value.
Ozone (O3) Generation
• Ozone is not stable molecule and the ozone
is generated at the point of application for
use in water treatment.
3 O2 ↔ 2 O3 Endothermic Reaction
Basic Ozone Generator
Cylindrical Electrode Schematic of Ozone Generator
• H2O2 can be added after ozone (ozone
oxidation and disinfection occur first).
• H2O2 can be added after ozone (H2O2 as a
pre-oxidant, followed by hydroxyl radical
• H2O2 and O3 can be added simultaneously.
Simplified Ozone System Schematic
Applications of O3/H2O2
in Water Treatment
• Taste and Odor Compound Oxidation:
O3/H2O2 can be applied to oxidize many
taste and odor causing compounds, which
are very resistant to oxidation (such as
geosmin, 2-methyliosborneol, MIB, and
• Synthetic Organic Compound Oxidation:
O3/H2O2 processes have been shown to be
effective in oxidizing halogenated
compound, such as 1,1-dichloropropene
(DCPE), trichloroethene (TCE), 1-
chloropentane (CPA), and 1,2-
Impact of O3/H2O2 on Other Water
• The applications of hydroxyl free radicals
generate biodegradable organic compounds
(BDOC) which can cause biological growth
in distribution systems.
• Hydroxyl radicals are strong oxidants that
interfere with addition of other oxidants,
such as chlorine, until the ozone residual is
• The oxidation of iron and manganese by
hydroxyl radicals generates insoluble
oxides that should be removed by
sedimentation or filtration. This may
increases the filter loading and backwash
Conventional Water Treatment
without O3/H2O2 Process
Applications of O3/H2O2 in the
Metropolitan Water District
• The Metropolitan Water District of Southern
California serve about 18 million people in six
counties. Metropolitan imports water from the
Colorado River and Northern California to
supplement local supplies, and develop water
conservation, recycling, storage and other resource
Water Treatment Plants Upgraded
All five of Metropolitan Water District’s water
treatment plants are being upgraded with O3/H2O2
• Henry J. Mills Water Treatment Plant in Riverside.
• Joseph P. Jensen Water Treatment Plant in
• Robert A. Skinner Water Treatment Plant near
Temecula is slated for completion in 2009
• Robert B. Diemer Water Treatment Plant in Yorba
• F. E. Weymouth facility in La Verne.
Process Flow Diagram in Metropolitan
Water District of Southern California
• Advantages and Disadvantages.
• Summary of O /H O
3 2 2
Advantages and Disadvantages
•O is able to destroy a wider range of organisms in
drinking water than chlorine, and It requires less
contact time than chlorine.
•O produces fewer potentially harmful disinfection
byproducts in drinking water than chlorination.
• Although it can result in the formation of bromate,
another potentially harmful byproduct, this
compound can be effectively controlled by
depressing the pH in the process.
• It is effective at removing objectionable tastes and
odors from the water. (e.g., the taste and odor
compounds formed by natural algae in the source
• Oxidation is more reactive and faster in O /H O
3 2 2
process compared with O3 molecular process.
Advantages and Disadvantages
• O /H O
3 2 process is effective in oxidizing difficult-to-
treat organics, such as taste and odor compounds.
• O /H O
3 2 process has been shown to be effective in
oxidizing halogenated compounds.
• Tendency to transfer organic compounds to more
biodegradable compounds may be increase with the
addition of H2O2.
• Pumps used to house H O 2 are not large; so space
requirements are not significant.
2 is strong oxidant and contact with personnel is
2 can be stored onsite, but deteriorates gradually
even when stored correctly.
Summary of O3/H2O2
Generation • O3 is instable and is generated at the point of use.
• H2O2 is purchased from chemical suppliers and can be
stored onsite, but it is subject to deterioration.
Primary Uses • Primary for chemical oxidation to remove SOC pollutants
and increase biodegradability of organic compounds.
• O3/ H2O2 is an effective disinfectant, but does not maintain
an appreciable ozone residual level.
Inactivation • O3/ H2O2 is one of the most potent and effective germicides
Efficiency used in water treatment.
Byproduct • If bromide is present in the raw water or if chlorine is added
Formation as a secondary disinfectant, halogenated DBPs may be
• Other byproducts: Include organic acids and aldehyeds.
Limitations • O3 should be used as a primary disinfectant prior to O3/
Points of • For disinfection, O3/ H2O2 should be after ozonation.
Application • Ozone contact should be before H2O2 addition.
• Application of O3/ H2O2 oxidation is before
coagulation/sedimentation or filtration.
Special • O3 generation is a complex process and subject to building
Considerations and fire codes. O3 is a highly toxic gas must be monitored.
• H2O2 is a hazardous material requiring secondary
containment of storage facilities.
• Aieta, E.M., K.M. Reagan, J.S. Lang, L. McReynolds, J-W Kang,
and W.H. Glaze. 1988. “Advanced Oxidation Processes for
Treating Groundwater Contaminated with TCE and PCE: Pilot-
Scale Evaluations.” J. AWWA. 88(5): 64-72.
• Duguet, J., E. Brodard, B. Dussert, and J. Malevialle. 1985.
“Improvement in the Effectiveness of Ozonation of Drinking
Water Through the Use of Hydrogen Peroxide.”Ozone Sci. Engrg.
• Ferguson, D.W., J.T. Gramith, and M.J. McGuire. 1991.
“Applying Ozone for Organics Control and Disinfection: A Utility
Perspective.” J. AWWA. 83(5):32-39.
• Ferguson, D.W., M.J. McGuire, B. Koch, R.L. Wolfe, and E.M.
Aieta. 1990. “Comparing Peroxone an Ozone for Controlling
Taste and Odor Compounds, Disinfection Byproducts, and
Microorganisms.” J. AWWA. 82(4):181.
• “Ozone in Drinking Water Treatment: Process Design, Operation,
and Optimization” Kerwin L. Rakness, American Water Works
• “Ozone in water treatment : application and engineering :
cooperative research report” Reckhow, David A; Brink, Deborah
R.; and AWWA Research Foundation, Lewis Publishers,
Langlais, Bruno, 1991.
• O”zone in water and wastewater treatment” Evans, Francis L.,
Ann Arbor Science Publishers, 1972.