SOIL, SEDIMENT AND SLUDGE: IN-SITU BIOLOGICAL TREATMENT
Phytoremediation
A typical Phyto-Remediation Process
Phytoremediation is a process that uses plants to remove, transfer, stabilize, and destroy contaminants in soil and sediment.
The type of plants used govern the quantity of water (and hence pollutants) drawn in, the depth of treatment and the specific contaminant that will be most effectively treated (most commonly poplar trees are used - fast growing with deep roots that draw up lots of moisture).
Variations of phytoremediation that have been used include wetlands to treat municipal sewage or neutralise acidic mine drainage.
The type of plants used govern the quantity of water (and hence pollutants) drawn in, the depth of treatment and the specific contaminant that will be most effectively treated (most commonly poplar trees are used - fast growing with deep roots that draw up lots of moisture).
Variations of phytoremediation that have been used include wetlands to treat municipal sewage or neutralise acidic mine drainage.
The Mechanisms of Phytoremediation :
1) Enhanced rhizosphere biodegradation
Uses:
Limitations:
- Occurs immediately surrounding plant roots.
- Plant roots naturally release nutrients to microorganisms in the soil - enhancing their biological activity.
- The roots also loosen the soil and then die, leaving water & aeration flow paths.
- The process typically draws the contaminated groundwater to the surface zone (drying the lower saturated zones).
- Contaminant drawn in by plant roots by phyto-extraction, resulting in the translocation/accumulation of contaminants into plant shoots and leaves.
- Plants produce enzymes such as dehalogenase and oxygenase, which help catalyse degradation.
- This process metabolises the contaminants within plant tissues due to the enzymes.
- Chemical compounds produced by plants immobilise contaminants at the interface of roots and soil.
- Volatile metals (such as mercury and selenium) are taken up, changed in species then transpired through the leaves.
Uses:
- Remediates: metals, pesticides, solvents, explosives, crude oil, PAHs, and landfill leachates - e.g. some plants can store metals in their roots, then would be harvested for the final removal.
- Some trees can remove organic contaminants & metabolize them to CO2 or plant tissue.
Limitations:
- Limited to shallow soils - limited by depth of roots.
- Too concentrated hazardous material can be toxic to the plant.
- Some locations are offer only seasonal treatment - when plant 'in season'.
- Can transfer contamination from soil to air.
- Not effective if very strongly/weakly sorbed contaminants.