Concept for in-situ anaerobic bio-remediation

This sheet is part of the BOSS application.


  • Infiltrating/injecting an organic substrate for in-situ anaerobic biological degradation
  • Infiltrating/injecting an organic substrate for in-situ anaerobic biological immobilisation

Administration of the substrate normally takes place (as liquid solution) via drains or vertical filters. If concentrated forms are administered, then direct push techniques can also be adopted, as can infiltration into the ground (excavation area or ‘mixed-in-place’). Further, there are also ‘slow-release’ application types whereby the organic substrate is administered via ‘socks’ which can be hung in vertical filters.


Field of application and application conditions

Many types of organic substrates can be used. These substrates can be divided into either fast-working or slow-working (“slow-release”). The known fast-working substrates are alcohols (ethanol, methanol), molasses, NutrolaseTM (= protamylasse), lactate, whey, ….Examples of “slow-release” substrates include HRCTM, possibly emulsified edible oils, Cap 18TM, …

• Hydrogen Release Compound (HRC™) is a poly-lactate ester which hydrolyses into lactate and glycerol upon contact with water. The release of lactate takes place slowly, whereby the released glycerol can also be used as a substrate.
• Edible vegetable oils like soya oil, maize oil and olive oil are slow-working because of their limited water solubility. This is why it is best to inject such edible oils as stable emulsion. An important effect of oil as an organic substrate is that to-be-cleaned organic pollutants like VOCl’s are directly partitioned to the oil phase. This phenomenon results in an immediate drop in concentration when the substrate is injected. In the long term, VOCl’s are released once again as the oil is metabolised by bacteria and dissolves. CAP-18™ is a commercially available variant which is based on soya oil.
• EHC™ is not an organic substrate, but a combination of fine-grain iron and an undefined organic substrate which can be injected into the soil as slurry or be implemented in shafts. Amongst other things, the iron will chemically reduce VOCl’s (see appropriate technical file), while the organic substrate may simultaneously create microbial de-chlorination.

The speed with which an organic substrate is used, once it is administered into the soil, is determined by many factors:

  • the type of substrate and the administered concentration/quantity
  • the physical form in which it is dosed (pure or diluted liquid, ‘syrup’, emulsion, pasta, solid/granular)
  • the way in which the substrate is administered (contact surface between the substrate and groundwater for slow-dissolving substrates)
  • the quantity of available electron acceptors at the location (oxygen, nitrate, sulphate, ironIII,…) which also result in substrate use
  • the microbial composition at the location and potential limiting factors like unfavourable pH, secondary pollutants, etc. 
  • the soil texture and groundwater flow speed (rougher texture and high groundwater speed result in faster dissolution and dispersion/dilution of the substrate
  • the temperature

Application for in-situ anaerobic dehalogenation of halogenated organic compounds

The substrate which is administered into the soil is fermented, whereby hydrogen gas is formed which acts as an electron donor for de-chlorinated micro-organisms, which can thereby convert VOCl’s into harmless end products. Other compounds, which can be biologically degraded in this way under anaerobic conditions, include chlorophenols, chlorobenzenes, and other halogenated organic compounds. 

The scope and dimensioning of the technique must always be determined in advance for ambiguous cases via a feasibility investigation and/or pilot phase.

For further reference, please refer to the Code of Good Practice for “anaerobic bio-remediation of VOCl’s”, which can be downloaded from the OVAM website (

Application for in-situ anaerobic bio-precipitation of heavy metals

The administration of an organic substrate can, if sufficient sulphate is present in the groundwater (>100 mg/L), result in the precipitation of heavy metals in the groundwater, via the forming of stable precipitates (primarily sulphides, formed by sulphate-reducing bacteria). This is possible for Zn, Pb, Cu, Cd, Cr… Precipitation-forming of carbonates, hydroxides or phosphates can also take place. If the groundwater does not naturally contain enough sulphate, it may be necessary to administer sulphate in addition to the organic substrate.

The scope and dimensioning of the technique must always be determined in advance for ambiguous cases via a feasability investigation.



There may be relatively large price differences between the various suitable substrates. The cost price (in 2006) for molasses/Nutrolase amounts to 0.5 to 1 euros/kg; for Post-lactate this amounts to ca. 2 euros/kg, while HRC costs ca. 16 euros/kg. Other factors also need to be considered when evaluating the ‘most beneficial’ carbon source, such as the total required quantity (molasses contain a lower level of ‘active’ carbon than, for example, Post-lactate), required means of administration, frequency, etc.

The costs for injection are namely determined by the required hardware (filters, pumps, mixing drums) and the total quantity of required substrates.


Environmental damage and to-be-implemented measures

For injection without simultaneous abstraction (recirculation), there is a risk of additional lateral dispersion of pollutants.

Volatile fatty acids, which cause odour problems, are created when the organic substrate is fermented.

Injection and recirculation of an organic substrate can result in blockages in filters and/or drains (bio-fouling and forming of mineral precipitates such as iron sulphides).

During the biological degradation of VOCl’s, dangerous intermediate products can be formed  (e.g. vinylchloride from the degradation of perchloroethylene).

During the bio-precipitation of heavy metals, these substances do not disappear from the soil. The long-term stability of the precipitates is thus a point of concern (if the precipitation is reversible, there may be an increase in the pollution intensity of groundwater over time).

In general, this clean-up technique causes little damage to the environment and there is minimum use of secondary raw materials, considering that pollutants are removed in-situ by micro-organisms, whereby no above ground purification is needed and no waste products are produced.