Bioremediation: enhanced bioremediation In Situ

Bioremediation: enhanced bioremediation In Situ

Type of treatment: Treatment

Description:
Stimulating bioremediation by addition of micro organisms (e.g., fungi, bacteria, and other microbes) and/ or nutrients (e.g. oxygen, nitrates) to the subsurface environment to accelerate the natural biodegradation process by the naturally occurring microorganisms of the soil. Bioremediation can take place under aerobic or anaerobic conditions.
 
There are four major processes, briefly described below.
Bio-Stimulation:
- Gaseous Nutrient Injection In this case, nutrients are fed to contaminated groundwater and soil via wells to encourage and feed naturally occurring microorganisms.
- Oxygen Enhancement with Hydrogen Peroxide as an alternative to pumping oxygen gas into groundwater.
- Nitrate Enhancement A solution of nitrate is sometimes added to the groundwater to enhance anaerobic biodegradation.
 
Bio-augmentation Sometimes acclimated microorganisms are added to the soil to increase biological activity. However, the efficiency of this technique is not as well proven as the bio-stimulation.

The first three methods are preferred because they stimulate the naturally occurring indigenous micro-organisms, already adapted to the environment. 


Waste:

Lightly oiled sediment (sand, gravel, soil, mud).
Oiled seaweed and vegetation (even fauna) may be treated


Situation/Possibilities in the country:

May be easily implemented on any polluted site (usually considered for coastal sheltered sites with slow natural clean-up by waves or inland sites).


Interest:

- it is relatively inexpensive with low energy requirements
- it can be carried out without elaborate equipment


Entry criteria:

Oil with a high asphaltene and resin content degrades slowly due to the molecular recalcitrance of the hydrocarbons while oil with a high aliphatic and aromatic content is a much more nutrient-dependent process and will degrade more rapidly within the adequate environment. It is recommended to carry out a GC/ MS analysis to define the composition of the oil and evaluate its biodegradability.
To achieve maximum biodegradation, sediment pore water should exhibit concentrations of 1.5 mg nitrate/litre, Phosphorous concentrations of approximately one-tenth of the nitrate levels, with oxygen levels above 2 mg/litre (Source: AMSA).
High permeability soils are required to allow the nutrients to reach the indigenous microorganisms (avoid fines clays).


Operational constraints:

Easy access to the treatment site.
Bio degradation is less efficient at low temperature.
Soil must be humid.
Pollutants must not be adsorbed to clay and/ or mud. In this case, they are unavailable for the micro organisms.


Impacts:

Under anaerobic conditions, contaminants may be degraded to a product that is more hazardous than the original contaminant.
Nitrate injection to groundwater is of concern because nitrate is a regulated compound. Bio-augmentation using non-native micro-organisms is also controversial.
The circulation of water-based solutions through the soil may increase contaminant mobility and necessitate treatment of underlying groundwater.


Legal constraints:

Refer to those applying to the management of polluted soils in situ. Special authorisation should be delivered for such work.


Efficiency:

Bioremediation is a long term process (months to year(s)).
Bioremediation degrades aromatics, N-alkanes and iso-alkanes. Resins and Asphaltenes are usually resistant to bioremediation. Cyclic hydrocarbons (Saturated and Aromatics) are partially biodegraded.
The efficiency of biodegradation can reach satisfactory levels when correctly implemented on biodegradable material.


Cost:

Limited, less than 30 euros / m3 (Source: KOLLER), 15 to 75 euros/ ton (Source: Bocard)
Related to the manpower, equipment for the spreading and purchase of stimulating agent.

published on 2019/12/10 14:45:51 GMT+0 last modified 2019-12-10T14:45:51+00:00