Fact sheet: Dehalogenation—ex situ

From: Public Services and Procurement Canada

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Description

Ex situ dehalogenation allows the rehabilitation of soils, sludge or sediments contaminated by chlorinated compounds such as polychlorinated biphenyls or dioxins and furans. This technology requires that the soil be excavated, crushed and/or separated as well as homogenized before being treated. It can be carried out using two different mechanisms, one involving sodium bicarbonate (base-catalyzed decomposition) and the other alkaline polyethylene glycol.

In the case of base-catalyzed decomposition, the soils are mixed with sodium bicarbonate and heated to 330 °C in a reactor, which allows a partial decomposition of the compounds as well as their volatilization. The gas emissions are collected and treated.

The use of an alkaline polyethylene glycol makes it possible, in turn, to replace the halogen of a chlorinated organic compound with polyethylene glycol, and thus reduce the toxicity of the treated compound. This reaction produces soluble compounds such as glycol ethers, hydroxyl and alkali metal salts. Soils are then washed and the leachate must be collected and treated. Once treated, soils can be reused to backfill the site.

Sources:

Implementation of the technology

Soils, sludge or sediments are excavated using conventional excavation equipment and sieved to separate and remove (or grind) overly coarse material (over 60 mm in diameter). If the water content is too high, drying may be necessary.

Base-catalyzed decomposition requires, after the treatment, the recovery and treatment of the gas emitted. This treatment may include adsorption using granular activated carbon, condensation or thermal oxidation (using direct flame, flame-free or catalytic oxides).

As for the use of alkali polyethylene glycol, the leachate produced must then be treated.

The implementation of this technology may include:

  • Mobilization, access to the site and setting up temporary installations.
  • Excavation of soil, sludge or sediment.
  • Installation of the necessary facilities for the drying of excavated materials if required.
  • Sieving and segregating materials to remove coarse material.
  • Installation of an electricity supply system for gas treatment.
  • Installation of a gas treatment and air emission control system, if required.
  • Installation of a wash water treatment system prior to discharge, if required.
  • Soils, sediments or treated sludge management (off-site disposal or backfilling on-site).
  • Restoration of the site following the excavation of the soil.

Materials and Storage

The implementation of this technology requires the use of construction equipment as well as civil engineering methods and conventional earthworks usually available for the excavation, sieving and homogenization of soils, sediments or sludge.

It also requires the installation of some specialized equipment. Transportable commercial equipment is available for both treatment processes. Chemicals include additives that are mixed with the soil.

If a thermal oxidizer is provided in the gas treatment chain during base-catalyzed decomposition, a source of natural gas or fuel oil is required. A connection to the local utility of natural gas can be made, but it is also possible to obtain a secondary electric combustion device.

Temporary piles of contaminated materials to be treated can be created on the site. In this case, they must be covered to limit the dispersion of dust, as well as the infiltration of water from precipitation, which could cause the runoff of contaminated soils to the surface as well as an increase of their water content which could affect the soil treatment.

Residues and Discharges

Ex situ dehalogenation produces solid residues (treated soils or sediments) and liquid or gaseous discharges, depending on the treatment mechanism used. The management of these discharges and residues must be done on the basis of their environmental quality, as to whether they should be disposed off-site or if they can be reused.

Used adsorbent materials (granular activated carbon) or other products used in gas processing must be recovered and disposed off-site in an authorized center.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Organic matter content
  • Metals concentrations
  • Contaminant concentrations present in the following phases:
    • adsorbed

Physical analysis

  • Soil water content
  • Soil granulometry
  • Presence of non-aqueous phase liquids (NAPLs)
  • Soil buffering capacity

Recommended trials for detailed characterization

None.

Other information recommended for detailed characterization

Phase III

  • Volume of contaminated material to treat

Notes:

Treatability testing in laboratories are recommended to determine the parameters that influence treatment time and cost as well as the presence of toxic residual products, which may be present at the end of the treatment.

Applications

  • This technique is applicable for contaminated soil, sediments, and sludge.
  • Specific to chlorinated pesticides and polychlorinated biphenyls contamination.
  • Allows the reduction of volatile and semi-volatile halogenated organic compounds concentrations.

Applications to sites in northern regions

The implementation of this technology requires the development of several infrastructure as well as the use of specialized equipment. The costs associated with their mobilization and their monitoring at the time of treatment are much higher for sites in northern regions. In addition, equipment availability is limited and work windows are relatively short. Thus, this technology could be expensive and difficult to put in place efficiently.

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
Does not exist
Free Phase
Does not exist
Physical
Applies
Residual contamination
Applies
Resorption
Applies
Thermal
Applies

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
Does not apply
Metals
Does not apply
Monocyclic aromatic hydrocarbons
Does not apply
Non metalic inorganic compounds
Does not apply
Pesticides
With restrictions
Petroleum hydrocarbons
With restrictions
Phenolic compounds
With restrictions
Policyclic aromatic hydrocarbons
Does not apply
Polychlorinated biphenyls
Applies


Notes:

Contaminants such as petroleum hydrocarbons and phenolic compounds could be partially or fully treated by the 330 °C heating required by base-catalyzed decomposition.

Treatment time

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

Long-term considerations (following remediation work)

None.

Secondary by-products and/or metabolites

Partial decomposition of chlorinated organic compounds can produce toxic by-products. Some ether glycol compounds produced with the alkaline polyethylene glycol dehalogenation technique may be toxic or recalcitrant.

Limitations and Undesirable Effects of the Technology

  • High clay and water content in the soil matrix may increase treatment costs.
  • Significant treatment and maintenance costs.
  • Not cost-efficient when applied to large volumes of contaminated soil or sediments.
  • Effluents must be treated before discharge, such as used leachate or gaseous effluents, depending on the process used.
  • Performance is reduced with certain types of halogenated organic compounds.
  • Debris must be removed from the soil matrix before the treatment.
  • Depth of the contamination may limit the application of this technology due to the prior excavation required.
  • The presence of infrastructure within or near the contaminated site may prevent the excavation of the contaminated material.
  • Dust control systems may be required during the handling of the contaminated soil.
  • Halogenated organic compound concentrations higher than 5% require a large quantity of reactive agents.
  • Potential to generate residual toxic compounds.

Complementary technologies that improve treatment effectiveness

Generally, there are no complementary technologies that improve dehalogenation treatment effectiveness. However, if there are contaminants present in the soil/sediment not targeted by this technology, such as metals, then solvent extraction can be added to the treatment processes.

Required secondary treatments

The base-catalyzed decomposition technique requires the collection and the treatment of the gas emissions. The dehalogenation with alkaline polyethylene glycol technique requires the collection and treatment of the leachate.

Application examples

Several private companies offer the dehalogenation technologies for the treatment of soil, sediment and sludge, and several examples specific to each company are available.

Application example of ex situ is available at the following site:

Performance

This technology is particularly useful for the remediation of soil contaminated with polychlorinated biphenyls. The alkaline polyethylene glycol technique successfully reduced polychlorinated biphenyls concentrations from 45,000 mg/kg to 2 mg/kg. Similarly, base-catalyzed decomposition has demonstrated reductions in polychlorinated biphenyls from 830 mg/kg to about 1 mg/kg.

Measures to improve sustainability or promote ecological remediation

  • Use of alternative energy and equipment with high energy efficiency.
  • Evaluation of raw material pretreatment choices to improve the efficiency of the treatment system (water content and soil grain size).

Process optimization to reduce waste and consumables.

Potential impacts of the application of the technology on human health

Main Exposure Mechanisms

Applies or Does Not Apply

Monitoring and Mitigation

Dust

Applies

Monitoring conditions favourable to dispersion during the excavation of the soil to be treated.

Atmospheric/Steam Emissions—Point Sources or Chimneys

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements]).

Atmospheric/Steam Emissions—Non-point Sources

Doesn’t apply

N/A

Air/steam—by-products

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements]).

Runoff

Applies

Monitoring of leachate water

Groundwater—displacement

Doesn’t apply

N/A

Groundwater—chemical/ geochemical mobilization

Doesn’t apply

N/A

Groundwater—by-product

Doesn’t apply

N/A

Accident/Failure—damage to public services

Applies

Examination of records and pre-excavation authorizations, implementation of special excavation procedures, preparation and repetition of emergency interventions.

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)

Doesn’t apply

N/A

Other—nonconforming backfill (processed or imported material)

Applies

Requires environmental and geotechnical control of materials used for backfilling

Other—soil leaching from stacks or open excavations

Applies

Reduction of leachate production, leachate collection and treatment, control of groundwater or surface water.

Other—Management of excavated soils, slurry and sediments

Applies

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

References

Author and update

Composed by : Mélanie Bathalon, B.Sc, MCEBR

Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada

Updated Date : April 28, 2014

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

Date Modified: