Fact sheet: Biopile—biological process—in situ

From: Public Services and Procurement Canada

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Description

The in situ biopile is a remediation technology used for the treatment of contaminated surface soils (less than 4 meters from soil surface). This technology is only applicable in the unsaturated zone and is for the treatment of soils contaminated with organic compounds.

The in situ biopile technique consists of periodic mixing of the soil to improve oxygenation which enhances the aerobic biodegradation of petroleum hydrocarbons. During the mixing process, there can be volatilization of volatile and/or semi-volatile contaminants, although this is not the objective of the technology. The addition of fertilizers to stimulate microbial activity and/or the addition of agents to improve the soil structure and to control soil water content are also options. It is important to monitor and control the ammoniacal nitrogen concentration, potential of hydrogen (pH), and soil water content in the contaminated biopile to avoid a reduction or an inhibition of microbial activity. A monitoring system, including down gradient observation wells, must be integral to an in situ biopile system to ensure that no contamination is leaching toward the groundwater or other sensitive receptors.

Sources:


Recommended analyses for detailed characterization

Biological analysis

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

Chemical analysis

  • Contaminant concentrations:
    • identification and concentration of all contaminants (sorbed, dissolved, and free phase)
  • pH
  • Nutrient concentrations includes:
    • lammonia nitrogen
    • total Kjeldahl nitrogen
    • nitrates
    • nitrites
  • Metals concentrations

Physical analysis

  • Dissolved oxygen concentration
  • Vadose zone oxygen, nitrogen dioxide, and methane concentrations
  • Soil water content
  • Soil granulometry
  • Contaminant physical characteristics including:
    • viscosity
    • density
    • solubility
    • vapour pressure
    • etc.
  • 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 optimal mixing rates

Other information recommended for detailed characterization

Phase II

  • Contaminant delineation (area and depth)

Phase III

  • Soil stratigraphy
  • Conceptual site model with hydrogeological and geochemical inputs

Applications

  • Applies to the treatment of residual contamination in soils to a depth of 4 meters from the surface
  • Principally applies to petroleum hydrocarbon contamination
  • Water content must be maintained between 50% and 80% of the total soil water holding capacity
  • The number of microorganisms should be maintained above 103 CFU/g (Colony Forming Units / gram soil)
  • The potential of hydrogen (pH) must be maintained between 6 and 8 to facilitate bacterial growth and activity

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

Notes:

Chlorobenzenes: suitable for chlorobenzene, dichlorobenzene and trichlorobenzene Phenolic compounds: suitable for cresol, pentachlorophenol and tetrachlorophenol Monocyclic Aromatic Hydrocarbons: applies with restrictions because these compounds are generally volatilized before being biodegraded.

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
Does not apply

Secondary by-products and/or metabolites

Generally, biodegradation of petroleum hydrocarbons does not generate any deleterious secondary by-products or metabolites.

Limitations and Undesirable Effects of the Technology

  • Requires accessible soil
  • Only applies to surface soil contamination (less than 4 meters from soil surface)
  • Climate influences the treatment conditions
  • Volatile organic compounds may impact air quality
  • A dust control system may be required during the soil mixing procedures
  • It is difficult to reduce petroleum hydrocarbon concentrations more than 95%, and/or obtain residual concentrations below 0.1 ppm
  • High contaminant concentrations can be toxic for the microorganisms
  • Soils must be well drained and able to maintain a water content between 50% and 80% of the total water holding capacity

Complementary technologies that improve treatment effectiveness

  • Air injection system
  • Thermal treatment such as hot air injection
  • Irrigation system to maintain water content
  • Run-off water and/or leachate collection to control the migration of the contaminants

Required secondary treatments

  • Gas emission collection system

Performance

The treatment time required for site remediation with the in situ biopile varies according to the concentration and characteristics of the contaminants, the natural microbial populations, and the physical and chemical properties of the soil.

References

Author and update

Composed by : Magalie Turgeon, National Research Council

Latest update provided by : Karine Drouin, M.Sc., National Research Council

Updated Date : April 1, 2008

Version:
1.2.1