Fact sheet: Chemical oxidation with permanganate—in situ

From: Public Services and Procurement Canada

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Description

Permanganate (MnO4-) oxidation is the most common and most used of all chemical oxidation techniques. Compared with other oxidants such as ozone or hydrogen peroxide, permanganate has a lower oxidation potential but it is more stable and more persistent in soils. As a result, it can migrate by diffusive and advective processes (FRTR, 2002), giving it a greater zone of influence. Oxidant delivery systems often employ vertical or horizontal injection wells using pressure to force the oxidant into the subsurface.

Potassium permanganate (KMnO4) and sodium permanganate (NaMnO4) are the most commonly used. Permanganate is available in liquid or crystalline form. Calcium or magnesium salts are also available. The injection solution is denser than water, which facilitates the vertical movement of the oxidant through the contaminated matrix, and improves contact between the oxidant and the contaminant. Permanganate oxidation is effective over a pH range of 3.5 to 12, but specific oxidation reactions are pH dependent. The oxidation reactions can lower the pH if the system is not adequately buffered. Degradation rates with permanganate also depend on temperature, organic matter content and reduced mineral species.

Permanganate is highly selective and is typically applied to degrade chlorinated ethenes but is not usually effective at oxidizing benzene, chlorinated benzenes, MTBE, carbon tetrachloride, or chlorinated ethanes. In some instances, permanganate has been used to degrade petroleum hydrocarbon compounds. The fact that it is available in a solid form makes it advantageous for transportation to remote sites. It has the major disadvantage of producing a purple colour which can be problematic if dilute permanganate solution can reach water bodies or sewers. Since it also produces a by-product of oxidized manganese, build up of manganese in soils can be an issue in some jurisdictions. Also, as any chemical oxidation process, it is not applicable in the presence of free phase.

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Implementation of the technology

In situ chemical oxidation (ISCO) with permanganate consists of injecting a solution of permanganate in the soils and/or groundwater using direct injection equipment on direct push rigs, trenches, infiltration galleries, well recirculation, deep soil mixing rigs, hydraulic fracturing equipment and other equipment may also be used. The objective is to bring the oxidant in contact with contaminants, mineralizing the contaminant, in the case of a complete oxidation, into carbon dioxide and water. For halogenated compounds intermediate compounds may be formed. Multiple injection events (usually two or three) are often required. The primary issue in chemical oxidation is the distribution of treatment media in the subsurface.

Implementation of permanganate oxidation projects may include:

  • Bench scale or pilot tests.
    Laboratory scale tests are generally required to determine optimal parameters such as oxidant quantities and concentrations. On-site pilot tests are used to determine the type of injection wells, the radius of influence and spacing of the injection wells, the concentrations and injection flow rates of oxidant solutions.
  • Mobilization, site access and temporary facilities
  • Reagent delivery, which could entail such measures as:
    • Injection well installation
    • Infiltration trench/drain construction
    • Injection or infiltration of aqueous treatment solutions
    • Deep soil mixing with solid or slurry reagents
    • Recirculation of groundwater amended with permanganate
    • Monitoring
    • Decommissioning of installed equipment (including groundwater wells)

Permanganate oxidation treatment doesn’t require activator, stabilizer or additive for pH adjustment.

Materials and storage

Solid or liquid forms of permanganate must be stored safely in a suitable and capped container, at ambient temperature and away from heat or incompatible materials.

Permanganate dust, which can be a health hazard, must be controlled during handling.

In some instances, oxidant reactivity with subsurface contaminants, including unexploded munitions and explosives, may be sufficient to result in combustion.

Waste and Discharges

Complete mineralization of organic compounds leaves carbon dioxide, water, and inorganic ions (like chloride). In some instances, complete mineralization doesn’t occur.

Sodium or potassium permanganate leaves elevated sodium or potassium levels and precipitated manganese dioxide (because of oxidation state, dissolved manganese is typically not an issue, but this may be confirmed through monitoring).

System installation typically requires drilling or excavating in contaminated areas, resulting in the handling and disposal of contaminated soils, typically containerized and disposed of off-site.

There is potential for contaminated or oxidant rich groundwater to flow out of the treatment zone. Properly designed injections do not result in uncontrolled flow of oxidants or contaminated groundwater along preferential pathways.

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
    • free

Physical analysis

  • Soil granulometry
  • Presence of non-aqueous phase liquids (NAPLs)

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.).

Physical trials

  • Vapour survey
  • Evaluation of the radius of influence
  • Evaluation of operating pressure/vacuum

Hydrogeological trials

  • Tracer tests

Notes:

Tests examining the effect of temperature change on hydraulic conductivity and establishing the zone of freezing with a pilot scale tubing system are recommended to properly design the full-scale containment system.

Other information recommended for detailed characterization

Phase II

  • Contaminant delineation (area and depth)
  • Presence of receptors:
    • presence of potential environmental receptors
    • presence of above and below ground infrastructure
    • the risk of off-site migration

Phase III

  • Soil stratigraphy
  • Identification of preferential pathways for contaminant migration
  • Volume of contaminated material to treat
  • Conceptual site model with hydrogeological and geochemical inputs
  • Characterization of the hydrogeological system including:
    • the direction and speed of the groundwater flow
    • the hydraulic conductivity
    • the seasonal fluctuations
    • the hydraulic gradient

Notes:

Pilot scale field tests are recommended for selecting the type and position of injection wells, establishing the radius of influence of the injection wells and to calculate optimal permanganate injection rates

Applications

  • Essentially for saturated zone treatment, vadose zone treatment is more complex and less efficient than the saturated zone, especially of the soil is very permeable as the oxidant requires sufficient contact time with the contaminant for the oxidation to occur;
  • Overall effective pH range of 3.5 to 12. For specific oxidation reactions narrower ranges of pH apply.
  • Specific for the degradation of polycyclic aromatic hydrocarbons (PAHs), chlorinated aliphatic such as perchloroethylene (PCE), trichloroethylene (TCE), dichloroethylene (DCE), and vinyl chloride (VC) and other organic contaminants
  • Soil permeability must be sufficient to allow oxidant migration.

Applications to sites in northern regions

In situ chemical oxidation (ISCO), for example, using campaign-based injection or the in situ mixing of solids is potentially applicable to remote northern sites, however, significant impediments to material transport and injection equipment mobilization must be overcome. Given the high cost of mobilizing reagents and equipment, ISCO may be pursued on a one-time basis with the objective of reducing concentrations to levels amendable to monitor natural attenuation or another alternative. Northern systems require climate-appropriate design, including consideration of permafrost and of seasonal changes in ground conditions.

Treatment type

Treatment type
Treatment typeApplies or Does not apply
In situ
Applies
Ex situ
Does not apply
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
Does not apply
Explosives
With restrictions
Metals
Does not apply
Monocyclic aromatic hydrocarbons
With restrictions
Non metalic inorganic compounds
Does not apply
Pesticides
With restrictions
Petroleum hydrocarbons
Applies
Phenolic compounds
Applies
Policyclic aromatic hydrocarbons
Applies
Polychlorinated biphenyls
Does not apply

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)

Long-term consideration associated with the implementation of permanganate oxidation includes:

  • Permanganate may persist in the aquifer up to several months after treatment. Depending on soil permeability and the presence of preferential pathways, permanganate could migrate over a significant distance, outside the site boundaries or arise in a surface water body nearby. Monitoring should detect potential migration of permanganate in water bodies as it can cause a purple colour in surface water.
  • Oxidants are consumed relatively quickly and do not persist long enough to penetrate low permeability materials. At many sites, contaminants continue to diffuse out of untreated low permeability structures, such as silt or clay lenses, for many years.
  • Soil sterilization post oxidation is not a major issue, as repeated investigations have demonstrated that microbial communities quickly recolonize the treatment areas.

Secondary by-products and/or metabolites

Chemical oxidation with permanganate produces carbon dioxide (CO2), water (H2O), and inorganic chloride during the oxidation of chlorinated organics. Degradation of contaminants by permanganate oxidation may produce toxic secondary by-products, depending on the nature of the contaminants. Volatile compounds may also be released.

By-product formation can be a concern if complete reaction cannot be obtained; bench top and/or pilot testing, as well as strict quality control for injected materials, is typically required. Oxidation products are usually (but not always) less toxic, more mobile and more biodegradable than parent compounds. For example, MTBE may degrade into acetone or tert butyl formate. Petroleum hydrocarbons may generate acetone or alcohols. Explosives (RDX and HMX) may create elevated levels of nitrate.

High levels of manganese oxides residue (MnO2) in soils can be an issue in some jurisdictions where manganese generic criteria for soils exist.

Limitations and Undesirable Effects of the Technology

  • Not suitable when there is free phase within the contaminated area.
  • Potential for purple groundwater seeping into surface waters or sewers
  • High levels of manganese oxides residue (MnO2) in soils can be an issue in some jurisdictions where manganese generic criteria for soils exist.
  • Soil permeability and matrix heterogeneity limit the application of the technology.
  • Potential for the oxidant to migrate through preferential pathways.
  • There is a risk of reduction in soil permeability during treatment due to CO2 entrapment, precipitation of KMnO4, etc.
  • Costs can quickly increase if large quantities of permanganate are required due to high concentrations of non-target oxidant consuming compounds (for example organic matter).
  • Special health and safety procedures are required for handling of a hazardous oxidant and controlling of hazardous permanganate dust.
  • The permanganate oxidation reactions may disrupt other remediation techniques, such as natural reductive dehalogenation.
  • Non-target organic carbon in the soil matrix may be mineralized which could reduce oxidant efficiency. This may also change the fate and transport of hydrophobic compounds; contaminants may be de-sorbed as total organic carbon is mineralized; in some cases this increases the effectiveness of the oxidant application by making more contaminants accessible for destruction.
  • Chemical oxidation deliberately causes extreme changes in geochemistry and creates a strongly oxidizing environment (to the extent that incompatible conduit, pipe or other underground materials can be damaged).
  • Metals can be mobilized within the treatment zone due to a change in oxidation states (such as chromium) and/or pH. Note that metals are generally attenuated by various mechanisms within a short distance of the injection site(s).
  • Injected fluids may displace (or “push”) contaminated pore water ahead of the injection front, leading to short-lived but dramatic changes in the distribution of groundwater contamination. Individual large-volume injections can “push” contaminated pore water at a substantial distance.
  • The formation of precipitates (such as manganese dioxide) associated with the injection of permanganate may clog the spaces between soil pores.
  • Spills of oxidants and/or improper mixing must be avoided. Energetic oxidation can ignite flammable materials; thermal decomposition can release oxygen and heat to intensify the blaze. Explosions can result, for example, if a gas-evolving reaction is contained or if incompatible materials (like hydrogen peroxide and potassium permanganate) are mixed.

Complementary technologies that improve treatment effectiveness

  • Free phase contaminants in soil should be removed prior to permanganate oxidation to optimize treatment efficiency.
  • The use of heat and/or co-solvents (tertiary butyl alcohol, acetone), and/or surfactant technologies to enhance NAPL dissolution or solubility have been demonstrated.
  • A number of proprietary formulations are available, several of which mix oxidants with oxygen-release compounds to stimulate post oxidation aerobic bioremediation. Soil sterilization post oxidation is not a major issue, as repeated investigations have demonstrated that microbial communities quickly recolonize the treatment areas.

Required secondary treatments

  • In situ chemical oxidation can be followed by a polishing biological to treat residual contamination.

Application examples

Application examples of chemical oxidation with permanganate are available in the following documents:

Performance

In situ permanganate oxidation is a well-proven technology that allows relatively quick treatment (from one to three years).

The long persistence of permanganate in the subsurface allows a better distribution of the oxidant, as compared to less persistent oxidants, especially in low-permeability soil.

According to the FRTR (2002), in situ chemical oxidation techniques can achieve high treatment efficiency (for example >90 percent) for unsaturated chlorinated aliphatic (such as trichloroethylene [TCE]) with very fast reaction rates (90 percent destruction in minutes).

Measures to improve sustainability of the technology

  • Schedule optimization for resource sharing and fewer days of mobilization.
  • Use of renewable energy and energy-efficient equipment (for example geothermal or solar energy for reagent delivery).
  • Evaluate source of oxidants (in other words, supply chain consideration in manufacturing.
  • Use of direct-push injection techniques.
  • Use of groundwater for on-site chemical solution preparation.
  • Evaluate delivery options by rail (for large volume of oxidants) rather than trucks.
  • Use of recyclable bulk solution containers.

Potential impacts of the application of the technology on human health

Unavailable for this fact sheet

References

Author and update

Composed by : Josée Thibodeau, M.Sc, National Research Council

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

Updated Date : March 1, 2009

Latest update provided by : Marianne Brien, P.Eng., Christian Gosselin, P.Eng., M.Eng., Golder Associés Ltée

Updated Date : March 22, 2019

Version:
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