Ozone H2 O2
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Ozone H2 O2

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    Ozone H2 O2 Ozone H2 O2 Document Transcript

    • CE 523 Ozone/Hydrogen Peroxide in Water Treatment Applications Andy Wang Spring 2009 Department of Civil & Environmental Engineering University of Southern California Los Angeles, CA 90089-2531
    • OUTLINE • Introduction • Reaction Mechanisms • Comparisons Between Ozone and O3/H2O2 in Water • Applications of O3/H2O2 in Water Treatment • Advantages and Disadvantages • Summary • Reference
    • Introduction • Regulatory Background • Advanced Oxidation Processes (AOPs) • About Ozone (O ) 3 • Property and Health Effect of Ozone and H O 2 2
    • Regulatory Background • 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 quality.
    • Advanced Oxidation Processes (AOPs) Definition • 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) 3 • Heterogeneous Catalytic Ozonation (HCO) • Photocatalysis (UV/TiO )2
    • About Ozone (O3) 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 Ozone (O3) • 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 (Contd.) Hydrogen Peroxide (H2O2) • HO2 is stored in a cool, dry, well-ventilated area and 2 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 2 2 flammable materials, will preferentially evaporate water until the concentration reaches sufficient strength, at which point the material may spontaneously ignite. • Low concentrations of H O , 3% or less, will 2 2 chemically bleach many types of clothing to a pinkish hue. Caution should be exercised when using H2O2 products.
    • Reaction Mechanisms 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 O3 − H+ HO2− H 2O 2 O2 O2− O2 HO2⋅ O3− + O3 O2 H HO4⋅ HO3⋅ OH⋅ O2 Ozone Decomposition Process by Hydroperoxide Ions
    • Summary of O3/H2O2 Chemistry • Hydroxyl radicals (OH·) are produced during the spontaneous decomposition of ozone. • 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 hydroxyl radicals.
    • 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 decomposition. Oxidation Reactions • 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 decomposition Ozone residual 5-10 minute Very short lived due to rapid reaction Ozone path Usual direct aqueous Primary OH· oxidation molecular ozone 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
    • O3/H2O2 Generation • 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 reactions ). • H2O2 and O3 can be added simultaneously. Simplified Ozone System Schematic
    • Applications of O3/H2O2 in Water Treatment • Taste and Odor Compound Oxidation: 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 chlorinated compounds). • Synthetic Organic Compound Oxidation: 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- dichloroethane (DCA).
    • Impact of O3/H2O2 on Other Water Treatment Processes • 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 quenched. • 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 frequency.
    • Conventional Water Treatment without O3/H2O2 Process
    • Typical Water Treatment with 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 management programs. Water Treatment Plants Upgraded All five of Metropolitan Water District’s water treatment plants are being upgraded with O3/H2O2 equipment. • Henry J. Mills Water Treatment Plant in Riverside. • Joseph P. Jensen Water Treatment Plant in Granada Hills • Robert A. Skinner Water Treatment Plant near Temecula is slated for completion in 2009 • Robert B. Diemer Water Treatment Plant in Yorba Linda. • F. E. Weymouth facility in La Verne.
    • Process Flow Diagram in Metropolitan Water District of Southern California O3/H2O2 Process
    • Summary • Advantages and Disadvantages. • Summary of O /H O 3 2 2 Disinfection Consideration
    • Advantages and Disadvantages Advantages •O is able to destroy a wider range of organisms in 3 drinking water than chlorine, and It requires less contact time than chlorine. •O produces fewer potentially harmful disinfection 3 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 waters). • Oxidation is more reactive and faster in O /H O 3 2 2 process compared with O3 molecular process.
    • Advantages and Disadvantages (Contd.) Advantages (Cond.) • O /H O 3 2 process is effective in oxidizing difficult-to- 2 treat organics, such as taste and odor compounds. • O /H O 3 2 process has been shown to be effective in 2 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 2 requirements are not significant. Disadvantages • HO 2 is strong oxidant and contact with personnel is 2 extremely dangerous. • HO 2 can be stored onsite, but deteriorates gradually 2 even when stored correctly.
    • Summary of O3/H2O2 Disinfection Consideration Consideration Description 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 formed. • Other byproducts: Include organic acids and aldehyeds. Limitations • O3 should be used as a primary disinfectant prior to O3/ H2O2 treatment. 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.
    • Reference • 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. 7(3):241-258. • 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 Association, 2005. • “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.
    • Thank You Andy Wang