Ozone Library
Ozone Fact Sheet
In this fact sheet on ozone, we find information on how ozone is produced and used, the Benefits of Ozone, and how it can be used safely.
- Ozone, or O3, is the tri-atomic form of oxygen. Stated simply, it is a molecule composed of three oxygen atoms.
- In nature, ozone is formed by reactions involving ultraviolet rays, or by the electrical discharge of lighting.
- Behind fluorine and hydroxyl radicals, ozone has the third-highest oxidation potential at 2.07 (see chart below).
- Ozone is 50 times more powerful and over 3000 times faster acting than chlorine bleach. During its short “lifespan,” ozone is highly reactive.
- The third molecule in O3 is bonded very loosely; it will break away, leaving pure oxygen, O2, and the single atom, O.
- Ozone is a high-energy molecule. Its half-life in water at room temperature is only 20 minutes, and it decomposes into simple oxygen.
- Because ozone can be produced on-site and on-demand, the effect is reduced chemical cost, storage, handling, and added plant safety.
- There are no toxic byproducts or potential health hazards when properly used as a microbicide,” said Myron Jones, EPRI Food Technology Center Manager. (Microbial contaminants include salmonella and giardia.)
Oxidation Potential of Ozone Compared to Other Oxidizers
Compound | Oxidation Potential | Relative power with respect to Chlorine |
---|---|---|
Fluorine | 3.06 | 2.25 |
Hydroxyl Radicals | 2.80 | 2.05 |
Ozone | 2.70 | 1.52 |
Hydrogen Peroxide | 1.77 | 1.30 |
Permanganate | 1.67 | 1.23 |
Hypochlorous Acid | 1.49 | 1.10 |
Chlorine | 1.36 | 1.00 |
EPA QUOTES ABOUT OZONE:
- Ozone is more effective than chlorine in destroying viruses and bacteria.
- The ozonation process utilizes a short contact time.
- There are no harmful residuals that need to be removed after ozone because ozone decomposes rapidly.
- After ozonation, there is no re-growth of microorganisms, except for those protected by the particulates in the wastewater stream.
- Ozone is generated on-site, and thus, there are fewer safety problems associated with shipping and handling.
- Ozonation elevates the dissolved oxygen (DO) concentration of the effluent. The increase in DO can eliminate the need for re-aeration and also raise the level of DO in the receiving stream.
OZONE O3
- Molecule
- 1840: C. F. Schönbein
- 3 oxygen atoms
- Properties
- Molecular weight: 48,00 g/mol
- Boiling point: -111,9°C (1 atm)
- Gas density: 2,144 g/l (0°C, 1 atm)
- Enthalpy of formation: 142,12 kJ/mol
- Solubility in water: 1370 mg/l (1 atm)
OZONE GAS CHARACTERISTICS
- Invisible at normal concentrations
- Has a distinct pungent odor
- Heavier than air (vapor density =1.65; air =1.0)
- Decomposes to oxygen molecules
OZONE:
- Is the strongest commercial oxidant
- Is a stron disinfectant
- Can form HO radicals for AOP
- Has a residual short-lived converts to O2
- Is Generated On-site
CHEMISTRIES OF OZONE IN WATER
DIRECT REACTION
- Cycloaddition, electrophilic reaction, electron transfer, oxygen atom transfer
- Highly selective reactions with a wide range of organics and inorganics
INDIRECT REACTION
- Decomposition into HO° (E° = 2.80 V) on initiation
- Fast and unselective reactions
- Scavenging effect
OZONE FEED GAS
- The first step in generating ozone is creating concentrated oxygen to feed the ozone generator.
- On average over 90% of all ozone equipment problems are due to poor quality air or oxygen.
OXYGEN INFO
- makes up 20.94% (by volume) of the air we breathe
- Is colorless, odorless, & tasteless
- The most widely occurring element on earth
- The second-largest volume of industrial gas produced
- Forms compounds with all chemical elements except the 9 noble gases
- Highly valued for its reactivity by itself & in its more reactive form, Ozone
HOW TO PRODUCE OXYGEN
- All systems utilize molecular sieve to perform the separation process
- The size of the sieve varies depending on the volume & pressure of air being separated
- The formula of the sieve varies depending on the function of the sieve
- The maximum purity that can be achieved with PSA & VPSA is 95.6%
METHODS OF OZONE GENERATION
- Ultraviolet (UV): Ultraviolet light at 185 nm generates a low concentration of O3.
- Corona Discharge: The most popular method for large and small applications. Used extensively for municipal water treatment
- Electrolysis: In-situ generation of ozone in water. Frequently used in high purity water applications cleanliness and low dissolved oxygen is important.
- Plasma Block: The most effective, reliable, and economic method. Used in wastewater, bottled water plants, and others.
OZONE CONTACTING SYSTEM
Factors Affecting Mass Transfer
- Gas-Phase Concentration
- Gas to Liquid Ratio (Vg/Vl)
- Pressure within the Contacting System
- Water Temperature
- Mixing (Gas/Liquid Interface Renewal)
- Contact Time
- Instantaneous O3 Demand
OZONE OFF-GAS DESTRUCTION
- Thermal
- Catalyst
- Thermal/Catalytic
- Chemical
- Deliver Off-Gas to other use locations
OZONE SAFETY
- Materials of Construction
- Ventilation
- Safety Monitoring
- Exposure Limits
- Ozone Destructs
SAFETY OZONE ADVANTAGES
- Ozone is not stored in bulk on-site
- The catastrophic large-scale release is not likely because generator shutdown stops ozone supply
- Ozone is not explosive or flammable
- leaks are identifiable – repair when they occur
- No reported fatalities from ozone exposure
IMPORTANT OZONE SAFETY CONCEPTS
- Automatic warning – You can smell ozone before it will harm you
- Effects of ozone exposure are a function of time and concentration
- First aid
- Low-level exposure – get fresh air
- High-level exposure – seek medical attention
- Fix leaks when they occur
OZONE HALF-LIFE
Typical Gaseous Ozone Half-life time as a Function of Temperature
Half-life time | Temp |
---|---|
∼ 3 months | -50 ºC |
∼ 18 days | -35 ºC |
∼ 8 days | -25 ºC |
∼ 3 days | 20 ºC |
∼ 1.5 hours days | 120 ºC |
∼ 1.5 seconds | 250 ºC |
Typical Dissolved in Water Ozone (PH=7) Half-life time as a Function of Temperature
Half-life time | Temp |
---|---|
∼ 30 minutes | 15 ºC |
∼ 20 minutes | 20 ºC |
∼ 15 minutes | 25 ºC |
∼ 12 minutes | 30 ºC |
∼ 8 minutes | 35 ºC |
- Gas-Phase ~ 20 minutes (20° C)
- at pH 6.0 ~ 20 minutes, at pH 7.0 ~ 15 minutes, at pH 8.0 ~ 5 minutes
RESIDUAL DISSOLVED OZONE DESTRUCTION
- UV at 254 nm wavelength.
- 90mJ/cm2 UV fluence is effective for 1 mg/l O3 destruction to below detectable limits in high purity water.
- Confirm UV sizing for the actual application
- Produces OH• radicals (short-lived) & O2
- Germicidal or TOC UV lamps both work
- Protects downstream process from undesirable O3 oxidation
WHY USE OZONE?
- Oxidation of organic color and odor compounds
- Microflocculation improves water clarity
- Reduced Chemical Consumption(residual sanitizer & pH)
- Improved Aesthetics
- Bather comfort (skin, eyes, hair)
- Reduced odors
- Superior disinfection protection
- Visibility