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
||Relative power with respect to Chlorine
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.
- 1840: C. F. Schönbein
- 3 oxygen atoms
- 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
- 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
- Cycloaddition, electrophilic reaction, electron transfer, oxygen atom transfer
- Highly selective reactions with a wide range of organics and inorganics
- 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.
- 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
- Deliver Off-Gas to other use locations
- Materials of Construction
- 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
Typical Gaseous Ozone Half-life time as a Function of Temperature
|∼ 3 months
|∼ 18 days
|∼ 8 days
|∼ 3 days
|∼ 1.5 hours days
|∼ 1.5 seconds
Typical Dissolved in Water Ozone (PH=7) Half-life time as a Function of Temperature
|∼ 30 minutes
|∼ 20 minutes
|| 20 ºC
|∼ 15 minutes
|∼ 12 minutes
|∼ 8 minutes
- 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