From: Public Services and Procurement Canada
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:
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:
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.
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).
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.
None.
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.
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.
The following sites provide application examples:
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).
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
Air / steam—by-products
Air stripping from heavily contaminated groundwater can create areas of high vapour concentrations in the treatment system enclosure. Vapour monitoring is required.
Runoff
Groundwater—displacement
Modelling the effects of required pumping and monitoring using pressure sensors
Groundwater—chemical/ geochemical mobilization
Groundwater—by-product
Accident/Failure—damage to public services
Records checks and pre-excavation permits, development of excavation or drilling 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/explosion
Other—Handling contaminated soils or other solid materials resulting from treatment
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
