13.1.2.4 Phyto-extraction (Phyto-accumulation, Phyto-absorption, or
Phyto-sequestration)
Plants take up or hyper-accumulate contaminants through their roots and store them
in the tissues of the stem or leaves. The contaminants are not necessarily degraded
but are removed from the environment when the plants are harvested. This is
particularly useful for removing metals from soil. The metals can be recovered for
reuse by incinerating the plants in a process called phytomining. It is mainly applied
to metals (Cd, Ni, Cu, Zn, Pb) but can also be used for other elements (Se, As) and
organic compounds. Elsholtzia splendens, Alyssum bertolonii, Thlaspi caerulescens,
and Pteris vittata are known examples of hyper-accumulator plants for Cu, Ni,
Zn/Cd, As, respectively.
13.1.2.5 Phyto-filtration
In this, plants concentrate and precipitate contaminants, particularly heavy metals or
radioactive elements from an aqueous medium through their root system or other
submerged organs. The plants are kept in a hydroponic system, whereby the
effluents pass and are “filtered” by the roots rhizofiltration or other organs that
absorb and concentrate contaminants. Plants with high root biomass or high absorption surface, with more accumulation capacity aquatic hyper-accumulators and
tolerance to contaminants achieve the best results. Examples include Helianthus
annuus, Brassica juncea, Phragmites australis, Fontinalis antipyretica and several
species of Salix, Populus, Lemna, and Callitriche.
13.1.2.6 Rhizo-degradation (Phyto-stimulation)
This process takes place in the soil or groundwater immediately surrounding the
plant roots. Exudates from plants stimulate rhizosphere bacteria to enhance biodegradation of soil contaminants (Fig. 13.1). Different treatment mechanism using
phyto remediation techniques given in Table 13.2.
13.1.3 Some of the Advantages of Phytoremediation Is Listed Below
In situ and passive technique.
1. Uses solar energy and is low cost.
2. Reduces environmental impact and contribute to the landscape improvement.
3. High acceptance by the public.
4. Reduction in dispersal of dust and contaminants by wind.
5. Reduction of surface runoff.
6. Reduction of leaching and mobilization of contaminants in soil.
7. Harvesting of the plants or organs that have accumulated metals is easy to
accomplish with existing technology.
8. The harvested biomass can be economically valuable.
9. Plant process more easily controlled than those of microorganisms.
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285
Phyto-sequestration)
Plants take up or hyper-accumulate contaminants through their roots and store them
in the tissues of the stem or leaves. The contaminants are not necessarily degraded
but are removed from the environment when the plants are harvested. This is
particularly useful for removing metals from soil. The metals can be recovered for
reuse by incinerating the plants in a process called phytomining. It is mainly applied
to metals (Cd, Ni, Cu, Zn, Pb) but can also be used for other elements (Se, As) and
organic compounds. Elsholtzia splendens, Alyssum bertolonii, Thlaspi caerulescens,
and Pteris vittata are known examples of hyper-accumulator plants for Cu, Ni,
Zn/Cd, As, respectively.
13.1.2.5 Phyto-filtration
In this, plants concentrate and precipitate contaminants, particularly heavy metals or
radioactive elements from an aqueous medium through their root system or other
submerged organs. The plants are kept in a hydroponic system, whereby the
effluents pass and are “filtered” by the roots rhizofiltration or other organs that
absorb and concentrate contaminants. Plants with high root biomass or high absorption surface, with more accumulation capacity aquatic hyper-accumulators and
tolerance to contaminants achieve the best results. Examples include Helianthus
annuus, Brassica juncea, Phragmites australis, Fontinalis antipyretica and several
species of Salix, Populus, Lemna, and Callitriche.
13.1.2.6 Rhizo-degradation (Phyto-stimulation)
This process takes place in the soil or groundwater immediately surrounding the
plant roots. Exudates from plants stimulate rhizosphere bacteria to enhance biodegradation of soil contaminants (Fig. 13.1). Different treatment mechanism using
phyto remediation techniques given in Table 13.2.
13.1.3 Some of the Advantages of Phytoremediation Is Listed Below
In situ and passive technique.
1. Uses solar energy and is low cost.
2. Reduces environmental impact and contribute to the landscape improvement.
3. High acceptance by the public.
4. Reduction in dispersal of dust and contaminants by wind.
5. Reduction of surface runoff.
6. Reduction of leaching and mobilization of contaminants in soil.
7. Harvesting of the plants or organs that have accumulated metals is easy to
accomplish with existing technology.
8. The harvested biomass can be economically valuable.
9. Plant process more easily controlled than those of microorganisms.
13 Phytoremediation and Nanoremediation
285