Fact sheet: Biosparging

From: Public Services and Procurement Canada

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Description

Biosparging consists of injecting pressurized air or gas into a contaminated zone in order to stimulate in situ aerobic biological activity. This remediation technique applies to dissolve and residual contamination in the saturated zone, and targets chemical compounds that can be biodegraded under aerobic conditions.

The injection of air (and gaseous nutrients if needed) favours the development of the aerobic microbial population by providing oxygen to the microbes and increases the interactions between air, water and aquifer, enhancing the bioavailability of the contaminants. The objective of a biosparging system is to promote contaminant biodegradation and to minimize the volatilization of volatile and semi-volatile organic compounds. The air injection flow rate is calculated to provide the quantity of oxygen required for enhancing bacterial degradation of contaminants. However, some volatilization may occur and depending on the chosen operation mode and design, air capture and treatment could be required.

Internet Links:

Environmental Protection Agency 2016. Chapter VIII: Biosparging In How To Evaluate Alternative Cleanup Technologies For Underground Storage Tank Sites: A Guide For Corrective Action Plan Reviewers. EPA 510-B-16-005; U.S.A.

Environmental Protection Agency Clu-in, 2016. Bioremediation—Aerobic Bioremediation (Direct), December 5th 2016

4.32 Air Sparging—FRTR Remediation Technologies Screening Matrix and Reference Guide, Version 4.0

Implementation of the technology

The injection method and the gas composition are two main possible variations in the biosparging system design. The gas injection can be performed using vertical or horizontal wells, and from trenches or reactive barriers. Nutrients are also introduced below the water table to enhance the microbial degradation activity to induce the destruction or transformation of contaminants of concern. The microbial population adapts to the new chemical and geochemical conditions. The treatment is stopped when contaminant concentrations reach treatment objectives.

Projects may include:
  • Mobilization, site access and temporary facilities
  • Reagent delivery, which could entail such measures as:
    • Groundwater well installation
    • Injection of amendment solutions
    • Injection of gasses below the water table (oxygen or air)

Installation of individual air injection blowers or a central blower and distribution pipe system for an injection system

    • Groundwater extraction, amendment and re-injection
  • Monitoring
  • Decommissioning of injection equipment

Materials and storage

  • Method relies on traditional/commonly available water well, drainage, water works and utility construction equipment and methods.
  • Tanks of oxygen gas, on-site oxygen generators or air compressors may be used. Additional injected materials vary widely according to contaminants, general groundwater composition and practitioners.
  • On-site storage is primarily a function of the compounds being applied to the groundwater systems and the manner of application. Projects using periodic injections of material may bring materials to the site on an as-needed basis and avoid on-site storage.

Waste and Discharges

  • If treatment is successful, the primary residual is microbial biomass (which decays over time). Excess reagent typically cannot be recovered, and is generally consumed in situ.
  • 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.Treated groundwater may transport bacteria, amendments, and degradation by-products out of the treatment zone. Hydraulic controls may be required.

Recommended analyses for detailed characterization

Biological analysis

  • Total heterotrophic and specific bacterial counts (according to the contaminants of interest)

Chemical analysis

  • pH
  • Organic carbon content
  • Metals concentrations
  • Contaminant concentrations present in the following phases:
    • adsorbed
    • dissolved
    • free
  • Nutrient concentrations including:
    • ammonia nitrogen
    • total Kjeldahl nitrogen
    • nitrates
    • nitrites
    • total phosphorus
  • Electron acceptor concentrations/reaction by-products including:
    • dissolved oxygen
    • nitrate
    • sulfate
    • ferric and ferrous iron
    • methane
    • dissolved manganese

Physical analysis

  • Dissolved oxygen concentration
  • Soil granulometry
  • Presence of non-aqueous phase liquids (NAPLs)
  • Evaluation of biological conditions and ecological factors

Recommended trials for detailed characterization

Biological trials

  • Microcosm mineralization trial
  • Biodegradation trial

Physical trials

  • Vapour survey
  • Evaluation of the radius of influence
  • Airflow rate
  • 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
  • Verify whether a confined aquifer is present
  • 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

Applications

  • Allows treatment of residual contamination within the saturated zone, as well as dissolved contamination in groundwater.
  • Suitable for remediation where the contaminants may be degraded or transformed under aerobic conditions.
  • Soil must be sufficiently permeable and homogeneous to allow efficient distribution of air or oxygen and nutrients;
  • Ideal when the soil pH range is from 6 to 8;

Applications to sites in northern regions

In situ biosparging is potentially applicable to remote northern sites where impediments to material transport and injection equipment mobilization can be overcome. Cold temperatures can hamper biodegradation and microbial activity may only occur during the summer months, thus treatment time may take several years. Microbial activity may be possible in deep soil as temperatures (below permafrost) are relatively constant over the course of the year.

Treatment type

Treatment typeApplies or Does not apply
In situ
Applies
Ex situ
Does not apply
Biological
Applies
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 technologyExist or Does not exist
Testing
Does not exist
Commercialization
Exist

Target contaminants

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


Notes:

Chlorobenzenes: suitable for chlorobenzene, dichlorobenzene and trichlorobenzene.
Phenolic compounds: suitable for cresol, pentachlorophenol and tetrachlorophenol.
Non-metallic inorganic compounds: suitable for ammonia-nitrogen only.

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

Notes:

Chlorobenzenes: suitable for chlorobenzene, dichlorobenzene and trichlorobenzene.
Phenolic compounds: suitable for cresol, pentachlorophenol and tetrachlorophenol.
Non-metallic inorganic compounds: suitable for ammonia-nitrogen only.

Long-term considerations (following remediation work)

Follow-up monitoring may be required to verify that the remediation objectives as well as applicable regulations are met once the groundwater system normalizes; after stimulation is withdrawn and excess biomass dies off. 

Secondary by-products and/or metabolites

Biodegradation of monocyclic aromatic hydrocarbons and petroleum hydrocarbons doesn’t usually generate any deleterious secondary by-products or metabolites. Issues with toxic intermediates may occur in the degradation of some explosives and pesticides. 

Limitations and Undesirable Effects of the Technology

  • In order to avoid contaminant spreading, biosparging should not be used in the presence of a free phase (LNAPL or DNAPL);
  • Preferential pathways and soil heterogeneity may cause unequal gas and nutrient distribution;
  • A vapour extraction and treatment system is required when there are buildings and/or below-grade infrastructure on or near the contaminated site;
  • The depth of contamination can be an obstacle;
  • A thin aquifer may require a tight injection well network;
  • The soil pH should be between 6 and 8;
  • Intrinsic soil permeability (k) should be higher than 10-10 cm2;
  • Biosparging can't be applied in a confined aquifer;
  • Air or gas injection enhances clogging of injection wells and soil pores when high ferrous iron and/or dissolved manganese concentrations are present.
  • By design, bioremediation will have large effects on parameters like oxidation-reduction potential, pH and total organic carbon. Bench top and/or pilot testing could be required.
  • Treatment is relatively passive: accident scenarios are relatively limited (with the exception of systems employing oxygen gas). If the treatment areas experience accident or upset conditions, contaminated groundwater may escape untreated.
  • Use of pure oxygen poses health, safety and environmental risks (fire, suffocation in confined space and explosion);
  • Very low concentrations of contaminants may not be attainable

Complementary technologies that improve treatment effectiveness

  • Addition of dissolved nutrients can, in some cases, promote the biodegradation process. Laboratory assays are sometimes recommended.
  • The addition of microbial strains (bioaugmentation) can also have an impact on the degradation rate or the transformation of contaminants.

Required secondary treatments

  • A vapour extraction and treatment system may be required when there are buildings or underground structures within or near the contaminated site.

Application examples

Application examples are available at these addresses:

Performance

Biosparging treatment time is highly variable, and depends on the contaminant properties, the natural bacterial population, and the physical and chemical properties of the contaminated site. Treatment times of 6 months to 2 years are often observed under favourable conditions.

Measures to improve sustainability or promote ecological remediation

  • Schedule optimization for resource sharing and fewer days of mobilization.
  • Use of renewable energy and energy-efficient machinery (for example: geothermal or solar energy for reagent delivery).
  • Select amendments with lower energy equipment for production. Select the type of gas (air versus oxygen) and the supply method (cylinders or produced on-site) with a lower carbon foot print.
  • Encourage amendment supply by local producers.
  • Use of groundwater recirculation to maximize the use of amendments and lower number of injection wells
  • Use of rainfall for amendments/nutrients mix for injection.
  • 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 : Magalie Turgeon, National Research Council

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

Updated Date : April 1, 2009

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

Updated Date : March 22, 2019

Date Modified: