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.)

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

• Gas-Phase ~ 20 minutes (20° C)
• Residual (Dissolved Ozone) – Decay
• 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