Fact sheet: Enhanced aerobic bioremediation

From: Public Services and Procurement Canada

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Description

Enhanced aerobic bioremediation is an in situ technique mainly used or the treatment of soil and/or groundwater contaminated with petroleum hydrocarbons, and non-halogenated volatile or semi-volatile organic compounds.

Aerobic biodegradation is a well know and proven technology with many modes of operation. The main advantage of this approach is the low cost while the main disadvantage is the long time frame sometimes required. This technique consists of providing oxygen (electron acceptor), nutrients, and/or other necessary compounds required to accelerate natural biodegradation of the contaminant by indigenous aerobic bacteria. Oxygen, which is often the primary factor limiting the growth of aerobic bacteria, can be added to the contaminated area using air or oxygen injection systems such as forced air injection, injection of oxygen saturated water, by the addition of chemical oxidants such as hydrogen peroxide, or by the addition of oxygen release compounds (ORC). Nutrients may be incorporated to the contaminated area in a dissolved (soluble commercial fertilizer), or gaseous form.

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Implementation of the technology

Enhanced aerobic bioremediation projects may include:

  • Pre-treatment laboratory and/or pilot-scale trials
  • Mobilization, site access and temporary facilities
  • Air, oxygen and reagent delivery systems, which could entail such measures as:
    • Injection/extraction well/tip installation
    • Infiltration trench/drain construction
    • Injection or infiltration of aqueous treatment solutions
    • Injection of slurries
    • Injection of gasses below the water table
    • Deep soil mixing with solid or slurry reagents
    • Groundwater extraction, addition of amendments and re-injection
  • Monitoring
  • Decommissioning of injection equipment

Nutrients and oxygen are introduced in the contaminated media to induce the destruction or transformation of contaminants of concern. The microbial population adapts to the new chemical and geochemical conditions, multiplying and acclimatizing. When contaminant concentrations reach treatment objectives, stimulating measures are withdrawn.

The primary issue with aerobic bioremediation is the distribution of treatment media in the subsurface and ensuring adequate environment for microbial growth.

Reagents are typically introduced in the saturated or unsaturated zone through injection or extraction wells. Trenches, sparging systems, infiltration galleries, in-well diffusers, groundwater pumping and re-injection, and other equipment may also be used.

Although it is not applicable to metal remediation, several approaches at the experimental stages have been used to reduce dissolved metals concentrations through biologically mediated sorption, sequestration or precipitation (particularly the formation of metal sulphides) by changing the valence state of metals; the long-term fate of metals in these systems and relative benefits of alternative approaches is the subject of ongoing research.

Materials and Storage

  • Injected materials vary widely according to contaminants, general groundwater composition and practitioners. A variety of proprietary mixtures are commonly used, including oxygen release compounds. Apart from air and oxygen common generic compounds used include urea (as a nitrogen source), ammonium nitrate (as a nitrogen source), dilute hydrogen peroxide, calcium peroxide, magnesium peroxide, etc. Tanks of oxygen gas, air compressors or vacuum pumps, or on-site oxygen generators may also be used.
  • On-site storage is primarily a function of the compounds being applied to the groundwater systems and the manner of application. A variety of proprietary mixtures are commonly used, including oxygen or hydrogen release compounds. Common generic compounds include urea (as a nitrogen source), ammonium nitrate (as a nitrogen source), dilute hydrogen peroxide, calcium peroxide, magnesium peroxide, etc. Tanks of oxygen gas, air compressors, or on-site oxygen generators may also be used.
  • 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 control 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
  • Oxidation reduction potential (Eh)
  • Organic carbon content
  • Organic matter 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

Physical analysis

  • Dissolved oxygen concentration
  • Temperature
  • Soil granulometry
  • Evaluation of biological conditions and ecological factors

Recommended trials for detailed characterization

Biological trials

  • Microcosm mineralization trial
  • Biodegradation trial

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
  • 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 vadose and saturated zones, 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 oxygen and nutrients;
  • Ideal when the soil pH range is from 6 to 8;

Applications to sites in northern regions

In situ aerobic bioremediation 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 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
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
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 time
Treatment timeApplies or Does not apply
Less than 1 year
Does not apply
1 to 3 years
Applies
3 to 5 years
Applies
More than 5 years
Applies

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 Adverse Impacts of the Technology

Limitations and Undesirable Effects of the Technology

  • This technology is not suitable when there is free phase within the contaminated area;
  • Low soil permeability limits application of the aerobic bioremediation technique;
  • Homogenous injection of amendments is difficult to obtain. Fractured, compacted, hydrophobic, stratified, and/or a heterogeneous soil matrix could cause preferential pathways during air or nutrient injection;
  • High contaminant concentration and/or the presence of a free phase could be toxic for microorganisms;
  • High concentration of metals may inhibit biodegradation;
  • Not suitable for inorganic contaminants except ammonia nitrogen;
  • High ferrous iron and manganese concentrations in groundwater could induce clogging of the well-screen slot openings and of the aquifer formation around the screen in the presence of iron-reducing bacteria;
  • By design, bioremediation will have large effects on parameters like oxidation-reduction potential, pH and total organic carbon.
  • 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.
  • Treatment is relatively passive: accidental scenarios are relatively limited (with the exception of systems employing oxygen gas, toxic co-metabolites, strong oxidants, strong acids, strong bases or strong reducing agents).
  • Use of oxygen poses health, safety and environmental risks (fire, suffocation in confined space and explosion);
  • If the treatment areas experience accident or upset conditions, contaminated groundwater may escape untreated.
  • Very low concentrations of contaminants may not be attainable.

Complementary technologies that improve treatment effectiveness

  • Thermal treatment (with a temperature kept below 40 °C);
  • Electrokinetic remediation;
  • Bioaugmentation.

Required secondary treatments

  • There is no required secondary treatment.

Application examples

Application examples are available at these addresses:

Performance

In situ aerobic bioremediation is a widely proven technology. This technology is often less expensive and results in fewer disturbances to the environment or site activities compared to ex situ technologies requiring excavation. The treatment time for complete remediation with aerobic bioremediation varies according to the type and concentration of contaminants, the microbiological population and activity, and the physical and chemical conditions of the contaminated site.

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
  • 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, 2008

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

Updated Date : March 22, 2019

Version:
1.2.1