Ozone is also used for in-situ remediation applications. Ozone has the third highest reduction potential of the oxidizers mentioned (slightly below the persulfate radical and the hydroxyl free radical). Ozone oxidizes organic compounds via two mechanisms:

• Direct oxidation by ozone
• Generation of free radical intermediates
  • Free radical attack occurs at a faster rate than direct ozone oxidation

The following is the basic reaction of ozone:


Ozone readily reacts with contaminants containing multiple bonds, such as ethylene (shown below). The initial step in this reaction breaks the double bond in ethylene and creates an intermediate (A) with two carbon-oxygen linkages. The reaction continues to form product B and oxygen. Complete reduction will result in carbon dioxide and oxygen. The reaction between ozone and contaminants containing single bonds does not readily occur. Ozone is frequently used in combination with another oxidant, such as hydrogen peroxide or ultraviolet (UV) light, to help remediate difficult to oxidize contaminants.

The use of ozone in groundwater can be adversely affected by pH, ozone concentration, and free radical scavengers, such as carbonates. In soil, ozone applications can be affected by the iron concentrations in the soil and humics. A typical ozone application uses 10 lbs of ozone per 1 lb of contaminant, and must be generated on-site from atmospheric or compressed oxygen. The capacity of generation is dependant upon the amount necessary for delivery (typical generators~100 lbs/day). Ozone can be applied to saturated and vadose zone materials, but requires a mass transfer from the gas phase to the aqueous phase.

Treatable Contaminants

Ozone is capable of remediating several compounds containing multiple bonds, including:

• BTEX and other petroleum hydrocarbons
• Naphthalene
• 3 and 4 ring polynuclear aromatic hydrocarbons (PAH)
• Phenols
• Sulfides
• Metals

Ozone Limitations

• Cost
• Health and Safety
• Must be produced on-site due to high reactivity and instability.
• Needs closely spaced air sparging wells for effective treatment
• Quantity needed
• Treatment programs typically require 100 lbs of ozone per day
• Require ozone saturation
• Unsaturated Zone Treatment