Fact sheet: Chemical Oxidation with Ozone - Ex Situ

From: Public Services and Procurement Canada

On this page


Ex situ chemical oxidation with ozone is a soil and groundwater remediation technology that involves the injection of gaseous ozone into contaminated soil or water to oxidize organic contaminants. The application of this technology requires the excavation and homogenization of soils or the pumping of groundwater to be treated as well as the management of soil or water after treatment. Oxidation treatment with ozone mineralizes the majority of organic compounds.

The destruction of contaminants is done directly by the ozone molecule or indirectly through hydroxyl radicals that are more reactive and less selective than ozone, which allows them to oxidize a wide range of chemical compounds. Ozone also oxidizes organic matter, producing carbon dioxide and water.

Chemical oxidation is suitable for all substances with oxidation potential, such as organic compounds and some metals. The advantage of ex situ treatment over in situ treatment is the control of oxidation conditions (e.g. contact time) and the certainty of a homogeneous distribution of the oxidant in the contaminated material.


Implementation of the technology

For the treatment of groundwater, extraction structures are put in place to collect contaminated groundwater and convey it to the treatment system, where it is treated and discarded.

The implementation of this technology may include:

  • Mobilization, access to the site and temporary facilities.
  • The construction of wells, collection trenches or the installation of permeable drains.
  • The installation of pumps and supply lines (often underground or in trenches designed to resist freezing and sheltered from traffic).
  • The installation of equipment necessary to generate ozone on the site.
  • Installation of a treatment system (mixing tank, oxidation system, etc.) (May require a small building or container).
  • The installation of a discharge system (evacuation to existing pipes, new surface water outlet, reinjection, infiltration field or infiltration basin).

For the treatment of contaminated soil, conventional excavation equipment is used to remove or mix the contaminated soil in shallow depths in order to proceed to on-site treatment. This can include:

  • Mobilization, access to the site and setting up temporary facilities.
  • Temporary storage and mixing of soils to ensure an even distribution of the soils to be treated.
  • Adding additives to increase soil porosity.
  • Treated soil management (off-site disposal, on-site application or backfilling of excavated areas).
  • The restoration of the surface.

Controls may be required for vapour and gaseous effluents if the contaminants in the treated soil or groundwater are volatile. Ozone is a toxic gas, therefore controlling ozone emissions is crucial.

Materials and Storage

  • This technology is implemented using traditional methods and equipment that are commonly available for excavation or development of wells, trenches or drains.
  • Treatment units can be built on-site or pre-assembled and transported in shipping containers, trailers or on pallets.
  • Treatment equipment requires the installation of an energy source.
  • Ozone gas is unstable and highly reactive and must be produced directly on the site before use, using ozone generators (ozonators). An ozonator is generally composed of an oxygen generator that extracts oxygen from atmospheric air and, under the action of an electric current, transforms oxygen molecules into ozone. Ozone storage is generally not performed since ozone is a toxic gas and is unstable in high concentrations.

Residues and Discharges

The implementation of the groundwater treatment system could lead to the management of contaminated soils resulting from drilling or excavation activities. In this case, these soils must be removed off-site.

Ozone leaves little residue other than oxygen. The complete mineralization of organic compounds produces carbon dioxide, water and inorganic ions (such as chloride). In some cases, complete mineralization does not occur. In most cases, chlorinated methanes are not oxidizable. Soil quality should be checked before reuse.

Generation of oxygen-rich vapours in the presence of large quantities of flammable contaminants (e.g. petroleum hydrocarbons) may pose safety concerns.

If sorbents are used (activated carbon) for the treatment of gaseous emissions emitted during processing, they must be recovered and managed off-site, when necessary.

Treated groundwater typically meets applicable criteria and does not pose a high risk when discharged. However, water quality monitoring is performed prior to discharge to ensure no unacceptable levels of by-products, reagents, or pH remain in the water.

Treated soils must be analyzed to determine proper disposal or reuse.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Organic matter content
  • Concentration of oxidant-consuming substances includes:
    • natural organic matter not considering the contaminants
    • reduced minerals
    • carbonate
    • other free radical scavengers
  • Contaminant concentrations present in the following phases:
    • adsorbed
    • dissolved

Physical analysis

  • Soil water content
  • Soil granulometry
  • Soil buffering capacity

Recommended trials for detailed characterization

Chemical trials

  • Evaluation of the matrix oxidant demand


On-site treatment trials will establish the efficiency of the technology and the parameters that influence the treatment time and cost (e.g. residence time, pump flow rate, requirements for pre-treatment, etc.).

  • Laboratory treatability testing (dosage)
  • Physical trials

    • Evaluation of optimal mixing rates

    Other information recommended for detailed characterization

    Phase III

    • Volume of contaminated material to treat
    • Volume or flow of water to be treated


    • Treatment of soils accessible by excavation.
    • Treatment of pumped groundwater.
    • Treatment of halogenated or non-halogenated volatile or semi-volatile organic compounds, petroleum hydrocarbons and pesticides.

    Applications to sites in northern regions

    Application of this technology in a northern region may be difficult because of the monitoring that such a system requires. Ozone production requires a minimum of supervision by specialized personnel. For remote sites, this implies greater mobilization and higher on-site monitoring costs. The availability of equipment is limited and requires additional mobilization. Work windows are relatively short considering that this technology involves either excavation of the soil or pumping of groundwater. These two activities, as well as the handling of soil or water up to the treatment unit, could require additional effort and cost at low temperatures and there is a risk of freezing.

    Treatment type

    Treatment type
    Treatment typeApplies or Does not apply
    In situ
    Does not apply
    Ex situ
    Does not exist
    Does not exist
    Dissolved contamination
    Free Phase
    Does not exist
    Does not exist
    Residual contamination
    Does not exist

    State of technology

    State of technology
    State of technologyExist or Does not exist
    Does not exist

    Target contaminants

    Target contaminantsApplies, Does not apply or With restrictions
    Aliphatic chlorinated hydrocarbons
    With restrictions
    With restrictions
    Monocyclic aromatic hydrocarbons
    Non metalic inorganic compounds
    Does not apply
    With restrictions
    Petroleum hydrocarbons
    Phenolic compounds
    Policyclic aromatic hydrocarbons
    With restrictions
    Polychlorinated biphenyls
    With restrictions

    Treatment time

    Treatment time
    Treatment timeApplies or Does not apply
    Less than 1 year
    1 to 3 years
    3 to 5 years
    Does not apply
    More than 5 years
    Does not apply

    Long-term considerations (following remediation work)

    Following soil treatment, whether used for backfilling excavations or for imported materials, environmental and geotechnical control of materials must be performed to ensure that soils do not exceed the applicable criteria for the site and do not create problems in terms of geotechnical stability or differential settlement.

    Secondary by-products and/or metabolites

    The oxidation of organic chemical compounds by hydrogen peroxide produces carbon dioxide. Obtaining toxic by-products may be of concern in the event of incomplete reactions. Laboratory tests and/or pilot tests, as well as strict quality control of the injected reagents (oxygen in this case) may be required. Products resulting from oxidation treatment are generally (but not always) less toxic, more mobile and more biodegradable than their precursors.

    Limitations and Undesirable Effects of the Technology

    • Presence of reactive species in the soil matrix (iron, manganese, carbonates) reduces the effectiveness of the treatment.
    • On-site production of ozone is required.
    • Ozone is highly reactive and noxious and cannot be stored.
    • Costs can increase rapidly if large quantities of oxidant are required.
    • Recovery of the gases produced (ozone and volatile compounds) may be required.
    • High soil humidity and organic matter content reduces the effectiveness of the treatment.
    • Low permeability soils (clayey to silty) are more difficult to treat.
    • Depth of contaminated soil to be excavated may limit technology application.
    • Infrastructures (aboveground or underground) can prevent soil excavation
    • Ex situ treatment costs may be higher than in situ treatment costs because of increased handling of the contaminated material.
    • Dust control during soil manipulation may be required.

    Complementary technologies that improve treatment effectiveness

    • If free-phase is present, a separation process must be implemented prior to the chemical oxidation treatment of soil or groundwater
    • Chemical oxidation using ozone combined with hydrogen peroxide injection is more aggressive when treating petroleum hydrocarbon contamination than with ozone alone.

    Required secondary treatments

    Gaseous emissions, when produced, must be collected and treated.

    Application examples

    The following websites provide application examples:


    Complete restoration potential in a short period of time; the chemical oxidation reaction by ozone is very fast and the treatment time varies from a few weeks to a few months.

    The advantage of ex situ treatment over in situ treatment is the control of oxidation conditions (e.g. contact time) and the certainty of a homogeneous distribution of the oxidant in the contaminated material.

    Measures to improve sustainability or promote ecological remediation

    • Optimization of the calendar to promote the sharing of resources and reduce the number of days of mobilization.
    • Use of renewable energy and low-energy equipment.

    Potential impacts of the application of the technology on human health

    Main Exposure Mechanisms Applies or Does Not Apply Monitoring and Mitigation
    Dust Applies only for soil treatment Monitoring conditions favorable to dispersion during the excavation of the soil to be treated.
    Atmospheric/Steam Emissions—Point Sources or Chimneys Applies according to the treatment system

    Integrate the collection and treatment of waste gases into the design,

    emission monitoring (choice of parameters, types of samples and intervention levels depending on source, risk and local requirements).

    Atmospheric/Steam Emissions—Non-point Sources Applies Estimation of the potential for vapor emissions, and monitoring of emissions to confirm predictions.
    Air/steam — by-products Applies Estimation of the potential for vapor emissions, and monitoring of emissions to confirm predictions.
    Runoff Does not apply N/A
    Groundwater—displacement Applies Modeling and monitoring using pressure sensors
    Groundwater—chemical/ geochemical mobilization Does not apply N/A
    Groundwater—by-product Does not apply (by-products are managed by the treatment system) N/A
    Accident/Failure—damage to public services Applies File checks and licensing prior to excavation or drilling, development of excavation procedures and emergency response
    Accident/Failure—leak or spill Applies Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions
    Accident/Failure — fire or explosion (inflammable vapours) Applies Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions
    Other - Accident/Failure - migration of gases and liquids along preferential pathways Does not apply N/A
    Other—Handling of contaminated soil Applies Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions


    Author and update

    Composed by : Mélanie Bathalon, B.Sc, MCEBR

    Updated by : Karine Drouin, M.Sc., National Research Council

    Updated Date : March 1, 2009

    Latest update provided by : Nathalie Arel, P.Eng., M.Sc., Christian Gosselin, P.Eng., M.Eng. and Sylvain Hains, P.Eng., M.Sc., Golder Associés Ltée

    Updated Date : March 22, 2019