Public Services and Procurement Canada
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.
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:
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:
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.
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.
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.).
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.
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.
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.
Gaseous emissions, when produced, must be collected and treated.
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.
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).
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