Fact sheet: Air striping

From: Public Services and Procurement Canada

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Description

Air stripping is an ex situ treatment that consists of extracting volatile and semi-volatile compounds that are readily stripped by evaporation from groundwater by flowing air through the contaminated water. Groundwater is first pumped into a device that promotes aeration. Exposure of water to air promotes volatilization of dissolved organic compounds and their transfer to the gas phase. Air stripping is a commonly used technology in groundwater pumping and as a treatment method.

Vaporized contaminants are not destroyed by this technology but are physically separated from the aqueous phase. The gaseous emissions must then be treated by a secondary system such as activated carbon filters, biofilters or catalytic oxidizers. After treatment, the treated water can be reinjected into the aquifer, discharged to a drainage system or discharged into a surface water body.

Sources:

Implementation of the technology

Wells, collection trenches, permeable drains or other structures are used to extract groundwater. The contaminated water is then sent either to an aeration tank or air stripper where it will be passed against the flow of forced air blowing in the aeration systems (packed tower or plateaued basin). The groundwater is dispersed using plastic, steel or ceramic nozzles while at the same time, air is injected against the current to increase its exposure and promote the air stripping of contaminants.

The airstream charged with extracted vapours is then treated by combustion (thermal oxidation, catalytic oxidation) or by filtration/adsorption (activated carbon, biofiltration). The treated water is then re-injected into the aquifer, directed to a sewer system or discharged into a surface water body.

The implementation of an air stripping system may include:

  • Mobilization, access to the site and setting up temporary installation.
  • Installation of wells, collection trenches and/or permeable drains.
  • The installation and connection of pumping equipment.
  • The installation and connection of air stripping and air handling equipment and control systems (which may require the construction of a building or the construction of a container).
  • Evacuation of treated water (injection wells, infiltration field, storm or sanitary sewer system, surface water, etc.).
  • The dismantling of wells and treatment equipment.

Materials and storage

This technology is implemented using traditional methods and equipment that are commonly available for development and installation of wells, water treatment systems, waterworks or utilities.
  • Processing units can be built on-site or pre-assembled and transported in shipping containers, trailers or pallets.
  • Treatment equipment requires the establishment of a power source and may require the use of maintenance products.
  • Treatment systems vary and may include the use of oxidants, biological substrates, adsorbents and/or different agents.
  • Construction and landscaping generally has little impact and requires little on-site storage.

Residues and rejects

The implementation of the 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.

Used adsorbent materials (e.g. activated carbon) or other products used in the treatment must be recovered and disposed off-site in an authorized facility. These residues may have characteristics associated with hazardous, flammable, corrosive or toxic materials.

Treated groundwater must meet all applicable criteria prior to discharge. If not sufficiently treated, it may pose a hazard to receiving environments (for example, water containing by-products or unacceptable pH).

Recommended analyses for detailed characterization

Chemical analysis

  • Alkalinity
  • Contaminant concentrations present in the following phases:
    • dissolved
  • Total suspended solids
  • iron
  • manganese

Physical analysis

  • Soil granulometry
  • Contaminant physical characteristics including:
    • viscosity
    • density
    • solubility
    • vapour pressure
    • etc.
  • Presence of non-aqueous phase liquids (NAPLs)

Recommended trials for detailed characterization

Physical trials

  • Gas permeability trials
  • Vapour survey
  • Evaluation of the radius of influence
  • Airflow rate
  • Evaluation of operating pressure/vacuum

Hydrogeological trials

  • Pumping 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.

  • Reinjection test under water table (if the water is reinjected in water table)
  • Other information recommended for detailed characterization

    None.

    Applications

    • Treatment of dissolved contamination only.
    • Ex situ treatment, but system installation can be done on the contaminated site.
    • Efficient for the treatment of semi-volatile and volatile organic contaminants halogenated or non-halogenated organic contaminants such as trichlorethylene or benzene, toluene, ethylbenzene and xylenes.

    Applications to sites in northern regions

    Ex situ air stripping is not always appropriate in remote areas that do not have easy access to utilities or local labour to maintain and operate the system. In addition, extreme cold can affect volatilization. Nordic systems generally require climate-friendly techniques, including deep freeze-up, seasonal changes in soil conditions, and long periods without operator intervention, refuelling sorbents.

    Treatment type

    Treatment type
    Treatment typeApplies or Does not apply
    In situ
    Does not apply
    Ex situ
    Applies
    Biological
    Does not exist
    Chemical
    Does not exist
    Control
    Does not exist
    Dissolved contamination
    Applies
    Free Phase
    Does not exist
    Physical
    Applies
    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
    Applies
    Chlorobenzenes
    Applies
    Explosives
    Does not apply
    Metals
    Does not apply
    Monocyclic aromatic hydrocarbons
    Applies
    Non metalic inorganic compounds
    Does not apply
    Pesticides
    With restrictions
    Petroleum hydrocarbons
    With restrictions
    Phenolic compounds
    With restrictions
    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
    Applies
    More than 5 years
    Applies

    Long-term considerations (following remediation work)

    None.

    Secondary by-products and/or metabolites

    Ex situ air stripping does not produce by-products, because the contaminants are transferred from the aqueous phase to the gaseous phase. Emissions from the air stripping system must be collected and treated.

    Limitations and Undesirable Effects of the Technology

    • Ex situ air stripping is less efficient for the elimination of certain semi-volatile contaminants.
    • This technology applies only to dissolved contaminants.
    • Airflow, water flow and water temperature are factors that can negatively affect the efficiency of the system.
    • If the water contains a lot of suspended organic matter, it is preferable to pretreat the water to prevent clogging of the system.
    • Oxidation removal of iron upstream of the air stripping unit is recommended to prevent or limit fouling.
    • Alkalinity or acidity of the medium may cause corrosion of the system. To avoid this, the solution must be neutralized before its introduction into the system.
    • The effectiveness of the system may be limited due to clogging caused by oxidation of minerals (iron and manganese) in the water, precipitation of calcium or growth of bacteria in the aerator.

    Complementary technologies that improve treatment effectiveness

    • Thermal treatment increases the efficiency of ex situ air stripping by facilitating the evaporation of less volatile organic compounds such as ketones.
    • The water treated by the air stripping system may require further treatment to meet the criteria for decontamination or site release.
    • Elimination of suspended solids, ferrous iron and dissolved manganese may be required to prevent precipitation in the system and to prolong the time between system maintenance procedures.

    Required secondary treatments

    • Vapours produced during the treatment must be collected and treated.
    • The treated water often contains low levels of contaminants and is further treated by filtration/adsorption (activated carbon, biofiltration).

    Application examples

    The following sites provide application examples:

    Performance

    Ex situ air stripping is effective for the removal of volatile soluble compounds such as BTEX and can reduce high concentrations such as 10,000 mg/l. Ex situ air stripping treatment removes an average of 90% of target contaminants (CSMWG, 2003).

    Measures to improve sustainability or promote ecological remediation

    • Optimization of the size of pumping and/or reinjection equipment.
    • Optimization of the work schedule to promote the sharing of resources and reduce the number of days of mobilization.
    • Use of renewable energy and low-energy equipment (geothermal, solar, etc.);
    • Passive or pulsed ventilation.
    • Use of biofilters for air treatment reduces energy demand and waste generation;
    • Extending treatment time to avoid winter operation, eliminating the need to winterize the system while reducing the amount of energy required.
    • Limiting the number of field visits using telemetry for remote monitoring of site conditions. 

    Potential impacts of the application of the technology on human health

    Main Exposure Mechanisms

    Applies or Does Not Apply

    Monitoring and Mitigation

    Dust

    Does not apply

    N/A

    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

    Does not apply

    N/A

    Air / steam—by-products

    Applies

    Air stripping from heavily contaminated groundwater can create areas of high vapour concentrations in the treatment system enclosure. Vapour monitoring is required.

    Runoff

    Does not apply

    N/A

    Groundwater—displacement

    Applies

    Modelling the effects of required pumping and monitoring using pressure sensors

    Groundwater—chemical/ geochemical mobilization

    Does not apply

    N/A

    Groundwater—by-product

    Does not apply

    N/A

    Accident/Failure—damage to public services

    Applies

    Records checks and pre-excavation permits, development of excavation or drilling 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/explosion

    Applies

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

    Other—Handling contaminated soils or other solid materials resulting from treatment

    Applies

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

    References

    Author and update

    Composed by : Mahaut Ricciardi-Rigault, M.Sc., MCEBR

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

    Updated Date : November 26, 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:
    1.2.5