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Ozone in Water Treatment Processes.pdf


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Ozone in Water Treatment Processes.pdf

  1. 1. 3/26/2017 Chemist/Ahmed Hasham 1 Ozone in Water Treatment Processes By/ Ahmed Mohamed Hasham
  2. 2. Ozone in Water Treatment Processes 3/26/2017 2 Chemist / Ahmed Hasham (Hesham)
  3. 3. About the presenter  Member of the Board scientists Egypt.  Member of Scientific Professions Syndicate.  Member of the Arab Society for experts and Safety Professionals.  Member of the International Association of Engineers.  Expert in water and waste water treatment technologies.  Certified trainer in water treatment field .  Certified trainer in Quality Management Systems field.  3/26/2017 Chemist/Ahmed Hasham 3
  4. 4. 3/26/2017 4 Chemist/Ahmed Hasham Contents 1. Introduction 2. Advances in Ozone Generation Techniques 3. The Ozone Contacting System 4. Drinking Water Treatment With Ozone. 5. Pre-ozonation 6. Points of application of ozone in a general water treatment scheme 7. Disinfection 8. Application of Ozone in Water treatment
  5. 5. Introduction  So far, ozone has been mainly used in disinfection, in the inactivation of viruses, decoloration , improvement of taste and odor of drinking water and in waste-water treatment.  Under today' s conditions, additional treatment steps are necessary.  Ozonation is introduced in the oxidation of organics ; This does not involve complete oxidation but yields products which can be removed by a subsequent treatment step. 3/26/2017 Chemist/Ahmed Hasham 5
  6. 6.  However, it has been shown that ozone is capable of doing more.  It is used as an oxidant in controlling biological contamination and in removing iron, manganese and other heavy metals by precipitation.  The latest findings indicate that preozonation enhances micro- flocculation and increases the filtration rate of rapid sand filters.  In all cases the application of ozone helps to decrease reliance on chlorine, which is thought to form by-products harmful to human health. 3/26/2017 Chemist/Ahmed Hasham 6
  7. 7.  Although the commonly used method of ozone generation by silent electrical discharge has been known for more than 130 years, there have recently been some very important advances in this technology which have made ozonation in water treatment more efficient and economic. 3/26/2017 Chemist/Ahmed Hasham 7
  8. 8. What is ozone? It is a molecule comprising of three oxygen atoms having the chemical symbol O3. ozone does exist naturally, it is a relatively unstable and reactive gas. As well as being a powerful disinfectant.  Today ozone is the strongest commercially available oxidant. Most commonly these have been water treatment for many different industries, and effluent treatment. 3/26/2017 Chemist/Ahmed Hasham 8
  9. 9. Ozone Generation  Electrical energy flowing across a narrow gap that is filled with oxygen splits the oxygen molecules into oxygen atoms (O). These atoms combine with other oxygen molecules (O2) to form ozone (O3).  Specific energy requirement = 0.820 kWh/kg O3  The actual specific energy requirement is much higher (10X to20X) due to generation inefficiencies 3/26/2017 Chemist/Ahmed Hasham 9
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  11. 11.  Economics has favored LOX-fed ozone systems since the late 1980s, when medium-frequency ozone generators, which produce ozone efficiently at high concentrations, were commercialized.  Oxygen containing feed gas can also be produced using pressure swing adsorption or vacuum-pressure swing adsorption (also called vacuum swing adsorption) technology to increase the oxygen concentration in the feed gas from ambient air levels (21 %vol) to greater than 90 %vol. 3/26/2017 Chemist/Ahmed Hasham 11
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  13. 13. Recognized methods FOR O3 generation There are four recognized methods:  Corona Discharge  Ultraviolet Radiation  Electrolysis Radiochemical 3/26/2017 Chemist/Ahmed Hasham 13
  14. 14. Corona Discharge  A high voltage passes through an air gap. In the case of ozone production, this high voltage transfers energy for the breaking of the O2 molecule, allowing the formation of a 3-atom oxygen molecule - ozone. This method is today the most widely used for commercial ozone production 3/26/2017 Chemist/Ahmed Hasham 14
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  16. 16. Ultraviolet Radiation  the formation of ozone from oxygen is endothermic, that is it requires energy. When exposed to light an oxygen molecule in a ground state will absorb the light energy and dissociate to a degree dependent on the energy and the particular wavelength of the absorbed light. The oxygen atoms then react with other oxygen molecules to form ozone.  For effective ozone production it is therefore necessary to utilize a short wavelength ~185nm. In theory, the yield of O3 from 185nm UV light is 130g/kWh of light. As lamp efficiencies are so low, ~1%, the production per kWh from the power source is greatly reduced. 3/26/2017 Chemist/Ahmed Hasham 16
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  18. 18. Electrolysis  Electrolysis is the process in which an electric current is passed through a liquid, causing a chemical reaction, resulting in the evolution of gases.  In relation to ozone production, water can be used as the electrolyte leading to direct diffusion, or special electrolytes such as H2SO4 can be used and ozone gas drawn off and diffused and contacted by the usual methods. 3/26/2017 Chemist/Ahmed Hasham 18
  19. 19. Radiochemical  High energy irradiation of oxygen by radioactive rays can promote the formation of ozone. Whilst high yields have been achieved under specific conditions using oxygen, the best results from an air flow through system at atmospheric pressure, has been ~ 3-4 mg/m3 . The process is fraught with complications in filtering harmful isotopes and it is not viewed with potential use in commercial applications. 3/26/2017 Chemist/Ahmed Hasham 19
  20. 20. Key Factors affected amount of ozone  The amount of ozone produced together with the efficiency and reliability of that production are directly related to a number of key factors the main ones being: -  Feed gas quality.  Power input.  Generation module construction.  Temperature. 3/26/2017 Chemist/Ahmed Hasham 20
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  23. 23. Advantage of Ozone application 1. That ozone can be produced from oxygen at higher ozone concentrations. 2. While consuming low to moderate specific energy (kWh/lbo,). 3. Has lowered operating costs. 4. Also, the number and size of ozone system equipment components have been reduced, lowering capital and maintenance costs. 3/26/2017 Chemist/Ahmed Hasham 23
  24. 24. Personal Exposure Effects and limits for Ozone  OSHA Permissible Exposure Limit: 8 hour 0.1 ppm  Short Term Exposure Limit 0.3 ppm  light; 0.08 ppm  moderate; 0.05 ppm  2 ppm Immediately Dangerous to Life or Health  5 ppm Respiratory Protection: Use full face self-contained breathing apparatus for entering areas with high concentration of ozone.  Lethal to small animals within 2 hours 15-20 ppm.  Engineering controls: use ozone destruct units (thermal and/or catalytic) for off gassing ozone.  Lethal in a few minutes >1,700 ppm. 3/26/2017 Chemist/Ahmed Hasham 24
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  26. 26. Leaks detection  These leaks can be located in one of the following three ways and should be repaired as soon as practical.  Leaks can be located using: 1. A portable ozone detector 2. A weak soap solution sprayed onto the potential leak area (bubbles will form as the gas escapes) 3. Chemical detection, whereby potassium iodide (2% KI) solution soaked on a white rag or white paper towel turns a brownish color in the presence of ozone 3/26/2017 Chemist/Ahmed Hasham 26
  27. 27. Applications in Drinking Water Treatment  All ozone applications involve oxidative reactions, whether ozone is used for disinfection or oxidation of specific Contaminants. DISINFECTION TREATMENT The primary purpose of ozonation at many water treatment plants is to achieve disinfection log-inactivation credit for viruses, Giardia, and Cyptosporidium at regulated or above-regulated levels. 3/26/2017 Chemist/Ahmed Hasham 27
  28. 28.  The value of 1-log inactivation is the same as 90% inactivation, 2 log is 99%, 3 log is 99.9%) etc.  The term log removal or log inactivation, instead of percent removal, is used in regulations for ease in disinfection reporting.  Bubble-diffuser contactors that are used for disinfection applications typically have 6, 8, 10, or 12 chambers.  Fewer chambers and shorter detention times (e.g., 6 to 10 min) are commonly used to meet Giardia and virus disinfection objectives, since required CT values are fairly low.  Extra chambers and additional detention time (e.g., 20 to 60 min) are used for enhanced disinfection applications. 3/26/2017 Chemist/Ahmed Hasham 28
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  30. 30. OZONE OXIDATION TREATMENT  Pre-ozonation 1. Improved particulate removal from filtration, as evidenced by lower turbidity and lower particle count of the filtered water. 2. Reduced coagulant dosage (e.g., alum or ferric). Also can used for :  Improved aesthetic quality through elimination of undesirable tastes, odors, and color.  Oxidized synthetic compounds including pesticides and solvents. 3/26/2017 Chemist/Ahmed Hasham 30
  31. 31. Iron and Manganese Oxidation  Iron and manganese are oxidized easily by ozone.  Soluble ferrous iron Fe(I1) is oxidized to ferric iron (FeIII), which slowly hydrolyzes to form particulate Fe(OH)3. The reaction consumes 0.43 mg of ozone per mg of Fe(I1)  Manganese oxidation by ozone and subsequent manganese removal is quite complex. Ozone oxidizes soluble manganese [Mn(II)] to form particulate removable) manganese dioxide [MnOz - Mn(IV)]. The reaction consumes 0.88 mg of ozone per mg of Mn(I1) 3/26/2017 Chemist/Ahmed Hasham 31
  32. 32. Hydrogen Sulfide Hydrogen sulfide is oxidized easily by ozone to form (ultimately) sulfate.  Oxidation proceeds in stages: 1. first forming insoluble elemental sulfur, which is evidenced by a light-colored colloidal suspension. 2. Further oxidation dissolves the elemental sulfur, forming soluble sulfite, and continued oxidation produces sulfate. 3. More ozone is required to completely oxidize sulfide to sulfate than is required to produce the insoluble, colloidal elemental sulfur. 3/26/2017 Chemist/Ahmed Hasham 32
  33. 33.  The theoretical O3 to H2S ratio is 3:l mg/L .  The operating O3 to H2S ratio is 4:1 mg/L. a. The selected operating ratio is higher so that a moderate ozone residual (0.2 mg/L to 0.3 mg/L in chamber 2) can be maintained. b. The ozone residual in the downstream chamber is used for process control. 3/26/2017 Chemist/Ahmed Hasham 33
  34. 34. Color Removal  Color in water is removed for at least two reasons: 1. Color is unattractive and is responsible for customer complaints. 2. Color is linked to the presence of fulvic or humic acids, which consume large amounts of chlorine and form halogenated organics.  Color can be removed sufficiently with coagulation in conventional and direct filtration water treatment plants, but color is removed very effectively by ozone oxidation. 3/26/2017 Chemist/Ahmed Hasham 34
  35. 35. Turbidity Removal Benefits of using Ozone before coagulation / filtration process : 1. Increased filtration rate by 33%. 2. lowered coagulant dose by 50% 3. Reduced filtered water turbidity by 50% 3/26/2017 Chemist/Ahmed Hasham 35
  36. 36. Ozone-based advanced oxidation treatment  Oxidation during ozonation also occurs via hydroxyl radicals(HO'), which are secondary oxidants that are formed by ozone decomposition via a complex mechanism.  processes in which 03 is purposefully decomposed into HO') are important in drinking water treatment because of reactions with organic molecules such as some solvents 3/26/2017 Chemist/Ahmed Hasham 36
  37. 37. Bromate Formation  Bromate formation and control has been the focus of intensive research efforts since the early 1990s when bromate (BrO3-) was implicated as a potential carcinogen.  BrO3- MCL value at 10 µg/L (USEPA, 1998).  Ozone plants can be subdivided into the following three categories, which relate to their relationship to bromate issues and considerations: 1. Bromide is absent in the source water or is present at low concentration. 2. Bromide is present in the source water at moderate concentration 3. Bromide is present in the source water at a relatively high concentration 3/26/2017 Chemist/Ahmed Hasham 37
  38. 38. 1. Bromide is absent in the source water  Bromide is absent in the source water or is present at low concentration. Bromate formation is proportional to bromide concentration for given water quality and ozone dose operating conditions. Low bromide concentration means low bromate formation potential. 3/26/2017 Chemist/Ahmed Hasham 38
  39. 39. 2. Bromide is present in the source water at moderate concentration  Bromide is present in the source water at moderate concentration (e.g., 50 to 100 µg/L), but ozone dose requirements are such that bromate formation is below the MCL value of 10 µg/L.  Bromate formation is minimized when: a. Ozone dose is low as a result of plant operation at low CT value that is still sufficient to meet the disinfection treatment objective, such as 2-log virus or 0.5-log Giurdia inactivation credit. b. Ozone dose is low even to meet elevated disinfection requirements (e.g., 0.5-log Cryptosporidium inactivation credit), because water quality characteristics are such that the ozone demand is low and ozone decay is slow (i.e., long ozone half-life). 3/26/2017 Chemist/Ahmed Hasham 39
  40. 40. 3. Bromide is present in the source water at a relatively high concentration  Bromide is present in the source water at a relatively high concentration such that bromate formation would exceed the 10 µg/L MCL value unless bromate mitigation measures are implemented.  Bromate mitigation options are described here and include lowering pH, adding ammonia, adding chlorine and ammonia, or using chlorine dioxide. 3/26/2017 Chemist/Ahmed Hasham 40
  41. 41. References  Kerwin Rakness-Ozone in Drinking Water Treatment_ Process Design, Operation, and Optimization-American Waterworks Association . 3/26/2017 Chemist/Ahmed Hasham 41
  42. 42.     00201159465989  00201146139692 3/26/2017 Chemist/Ahmed Hasham 42