Fact sheet: Chemical oxidation with peroxide—ex situ

From: Public Services and Procurement Canada

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Description

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:

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).
  • 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 outlets, reinjection, infiltration field or infiltration basin) to receive the liquid discharges from the treatment. 

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:

  • 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 permeability.
  • 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.

Materials and Storage

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.

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.

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
  • Reaction parameters include:
    • kinetic
    • stoichiometry
    • thermodynamic parameters
  • 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

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.).

  • 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

    Applications

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

    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. 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.

    Treatment type

    Treatment type
    Treatment typeApplies or Does not apply
    In situ
    Does not apply
    Ex situ
    Applies
    Biological
    Does not exist
    Chemical
    Applies
    Control
    Does not exist
    Dissolved contamination
    Applies
    Free Phase
    Does not exist
    Physical
    Does not exist
    Residual contamination
    Applies
    Resorption
    Applies
    Thermal
    Does not exist

    State of technology

    State of technology
    State of technologyExist or Does not exist
    Testing
    Does not exist
    Commercialization
    Exist

    Target contaminants

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

    Treatment time

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

    • Efficient at a pH between 2 and 5.
    • Chemical oxidation is an exothermic reaction which can increase the volatilization and/or desorption as well as the biodegradation of contaminants
    • Potential for incomplete oxidation.
    • It may be necessary to recover and treat the gases produced during oxidation (volatile compounds).
    • Presence of compounds other than the contaminants to be treated may react with the oxidant reduce the efficiency of the technology.
    • Costs can increase rapidly if large quantities of oxidants are required
    • High soil humidity and organic matter content reduce the effectiveness of the treatment.
    • Low permeability soils (clayey to silty) are more difficult to treat.
    • The depth of contaminated soil to be excavated may limit the application of the technology.
    • Infrastructure on or near the site can prevent soil excavation, eliminating the ex situ treatment option.
    • Ex situ treatment costs may be higher than in situ treatment costs due to increased handling of the contaminated material.
    • Dust control during soil manipulation is necessary.

    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.

    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.

    Required secondary treatments

    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.

    Application examples

    The following websites contain application examples:

    Performance

    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.

    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.
    • Assessment of the oxidant source (for example: supply chains as part of the manufacturing process).
    • Use of groundwater for the preparation of chemical solutions on the site.
    • Review of transportation methods to reduce green gas emissions.
    • Use of recyclable bulk solution containers.

    Potential impacts of the application of the technology on human health

    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

    Applies

    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

    Applies

    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

    Applies in cases of groundwater treatment

    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

    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—Handling of contaminated soils

    Applies

    Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions

    References

    Author and update

    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

    Version:
    1.2.1