Phytoremediation Information and Technology

The process commonly referred to as phytoremediation is implemented by establishing a plant or community of plants that have been selected to provide the required remediation mechanisms. The technology exploits the natural hydraulic and metabolic processes of plants, and thus is passive and solar driven. The technology can be used in combination with mechanical treatment methods or as a "stand alone" treatment method.

Phytoremediation can be used to treat a wide range of organic and inorganic contaminants. Phytoremediation has been effective for the removal of nitrates and ammonium from the groundwater. All plants require a nitrogen source to grow. Some nitrogen-containing contaminants can be used by the plants for plant growth.

Sites contaminated with heavy metals can be remediated using phytoremediation. Accumulation usually results in 1% Cu and Co and 3% Zn, Ni, Mn on a dry weight basis. The use of hyperaccumulating plants is in the beginning stages and further research is required to develop plants with greater biomass.

Phytoremediation may be useful in treating volatile organic compounds (VOCs), chlorinated VOCs (CVOCs), and trinitrotoluene (TNT). The technology is in its infancy for the treatment of contaminants of these types. Projects that target organic contaminants, such as trichloroethylene (TCE) and TNT, in the water phase have shown some promise; however, more research is needed for the less-mobile contaminants, such as polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs).

Stabilization and removal processes

Stabilization Processes
Phytostabilization - The use of plants to increase sequestration of contaminants (usually metals) in the soil. Soil sequestration occurs as plants alter water flux and reduce contaminant mobility. Plants and microbial enzymes bind contaminants into soil (humification). Plants also incorporate free contaminants into plant roots (lignification) and prevent wind and water erosion

Removal Processes
Phytoaccumulation/Phytoextraction - Specific species of plants are used to absorb unusually large amounts of metals from the soil and are subsequently harvested from the growing area. The biomass is composted to recycle the metals or incinerated and the ash is sent to a landfill. Typically used for remediation of metals-contaminated soils, sediments, and groundwater.

Rhizofiltration - Similar to phytoextraction; however, plant root systems usually are first developed to maturity in an aqueous environment within a green house. When the root system is developed, contaminated water (generally with metal contamination) is brought to the plants and circulated through their water supply.

Phytodegradation - The process where plant enzymes completely mineralize or partially break down contaminant compounds.

Rhizo(sphere)degradation - The symbiotic relationship that occurs between plant root systems and microorganisms in the root zone. Plant roots excrete sugars, acids, and alcohols that contain organic carbon that microorganisms use as a food source. This provision enhances microbial activity in the root zone, resulting in a microbial contribution to soil contaminant degradation.

Organic Pumps - The use of plants to control the migration of contaminants in the groundwater by exploiting their natural hydraulic properties. Using trees for water control is estimated to cost approximately one half the cost of traditional pump-and-treat systems.

Phytovolatilization - The use of plants to remove contaminants from the subsurface and evaporate or volatilize the contaminants from the leaf surface of the plant once it has traveled through the plant’s system