From: Public Services and Procurement Canada
Ex situ chemical oxidation with hydrogen peroxide is a remediation technology that requires the excavation and homogenization of soils or the pumping of groundwater as well as the management of soil or water after treatment. This technology reduces the concentration of organic contaminants present in the contaminated matrix.
The peroxide oxidation reaction alone is not strong enough to completely degrade organic compounds. However, when mixed with a catalyst such as ferrous iron (Fe2+) to form the Fenton reagent, the oxidation potential of the hydrogen peroxide increases. The hydroxyl radicals produced during the decomposition of hydrogen peroxide in the presence of ferrous iron are highly reactive and non-specific and can efficiently treat hydrocarbons. Chemical oxidation therefore occurs for all substances having oxidation potential, such as metals or organic compounds.
The Fenton reaction is pH dependent, with maximum efficiency in acidic environments and reduced effectiveness under alkaline conditions. However, stabilizers (chelating agents) have been developed to improve the effectiveness of oxidation at higher pHs.
Sources:
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 for 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.
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.
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 doesn’t 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 for conformity before reuse.
Notes:
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. 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 or 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 may be required. Products resulting from oxidation treatment are generally (but not always) less toxic, more mobile and more biodegradable than their precursors.
If free phase is present, a separation process must be implemented prior to the chemical oxidation treatment of soil or groundwater.
If the treated soil or groundwater doesn’t meet the applicable reuse or discharge criteria, then an additional treatment step, depending on the level and type of contamination, may be required.
Gaseous emissions must be collected and treated. If the contaminated soil is treated with a peroxide solution, leaching water can be generated and must be collected and treated.
The following websites contain application examples:
Potential for remediation in a short period of time.
The advantage of ex situ treatment over in situ treatment is the control of oxidation conditions (for example: contact time) and the certainty of a homogeneous distribution of the oxidant in the contaminated material.
Main Exposure Mechanisms
Applies or Doesn’t Apply
Monitoring and Mitigation
Dust
Applies only for soil treatment
Monitoring conditions favourable 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 vapour emissions, and monitoring of emissions (choice of parameters, types of samples and levels of intervention depending on source, risk and local requirements) to confirm predictions.
Air/steam—by-products
Estimation of the potential for steam emissions and monitoring of emissions (choice of parameters, types of samples and levels of intervention depending on source, risk and local requirements) to confirm predictions.
Runoff
Monitoring of the discharge point or perimeter, selection of parameters, sample types, and frequencies according to source, risk and general requirements, minimize generation and migration of water.
Groundwater—displacement
Applies in cases of groundwater treatment
Modelling and monitoring using pressure sensors
Groundwater—chemical/ geochemical mobilization
Geochemistry modelling, laboratory testing and/or pilot testing, monitoring the groundwater quality
Groundwater—by-product
Doesn’t apply (by-products are managed by the treatment system)
N/A
Accident/Failure—damage to public services
File checks and licensing prior to excavation or drilling, development of excavation procedures and emergency response
Accident/Failure—leak or spill
Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions
Accident/Failure—fire or explosion (inflammable vapours)
Other—Handling of contaminated soils
Composed by : Serge Delisle, Eng. M.Sc., National Research Council
Updated by : Karine Drouin, M.Sc., National Research Council
Updated Date : April 16, 2013
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
