Phytoremediation:
A plant-microbe-based remediation
system
Introduction
• Rational
• Economic potential
• Public acceptance and regulatory
considerations
Principles of phytoremediaiton
Phytoremediaiton of heavy metals
Phytoremediation of organics
Phytoremediation—
Refers to the use of green or vascular plants
for removal of organic and inorganic
contaminants. It may be applied to:
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Phytoextraction
Phytostabilization
Phytofiltration
Phytovolatilization
Phytodegradation
Phytoextraction
The use of metalaccumulating plants that can
transport and concentrate
metals from the soil to the
roots and aboveground shoots.
• high biomass production
• handling ease
Cd
• established cultivation practices
To increase the efficiency of
phytoextraction, e.g. addition of
chelators to contaminated soil.
As
Cu
Zn
Pb
Phytostabilization
The use of plants to control the
movement of water underground, or
soil amendments are also applied to
contaminated soil to reduce the
bioavailability of the contaminants.
Also termed as inplace inactivation
or phytorestoration.
• Effective in immobilizing watersoluble
contamination
and
preventing migration
• But it does not remove
contaminants from the site.
As
PCBs
2,4-D
TNT
Pb
H2O
H2O
H2O
•
The site is planted into vegetation, which reduces off site
migration of the stabilized soil matrix and contaminant
through water usage and erosion control.
•
Plant are chosen to maximize root uptake of contaminant
and would sequester the material in the root tissue and
potentially help catalyze the formation of insoluble
contaminant species such as Pb-pyromorphite
[3Pb3(PO4)2.PbCl2--lead phosphate chloride].
e.g. Fast-growing poplars with deep roots are able to absorb
and transpire large quantities of water from the roots through
shoots into the atmosphere.
Hybrid Poplar Field at Edward Sears Property
Rhizofiltration
The use of plant roots to absorb, concentrate, and
precipitate heavy metals from water.
(1) The roots of sunflowers have been used to treat water
containing lead, uranium, strontium, cesium, cobalt, and zinc
to concentrations below the accepted water standards.
(2) This approach has been used to remove uranium from
groundwater on sites at Ashtabula, OH, and Oak Ridge, TN,
and to remove cesium and strontium from a pond near the
Chernobyl reactor.
The presence of other metal ions does not substantially interfere
with rhizofiltration of lead, cesium, or strontium, suggesting that
this approach can be used to remove target metals from mixtures
containing different metal ions
Phytoremediation—
Initially, the term has been closely associated
with the potential use of hyperaccumulator
species, plant being able to accumulate unusual
levels of metals in their tissues.
Recently, the scope has been extended to
include other plant-based processes that result
either in containments or removal of pollutants,
e.g., immobilization, degradation and
volatilization (Wenzel et al., 1999).
 Most of the hyperaccumulators are rather
small herbaceous plants growing on
naturally metalliferous sites or on old
mining deposits.
 Because of the low-biomass limitation of
hyperaccumulator species, high-biomass
vegetation, such as trees and grass are
being evaluated as an alternative, even
though the bioconcentration of metals is
typically well below that found in the
former.
Economic potential
Based on Kruger et al., 1997, non-biobased remediation technology cost:
in situ: $10 to $100 / m3
ex situ: $30 to $300 / m3
Specialized techniques such as in situ
vitrification can easily surpass $1000/m3.
In comparison:
Land farming can be as low as $0.05/m3/year
• Economical potential is the major driving
force over agriculturally-based soil
remediation.
• Agricultural practices developed for soil
management with its primary goal for
maintaining soil quality have applicability
in soil remediation.
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Raskin and Ensley, 2000
International Market
The US market account for 35 to 45% of the total
world environmental spending.
The size of the remediation market in the entire
EU is just below half that of the US. However, the
forces driving remediation markets in Europe
tend to lag behind those of the US.
Public acceptance and regulatory
considerations
What do you prefer in your neighborhood?
Large earth-moving equipment and long-term
exposure to dust and other air pollutants.
vs.
Orderly plots of plants, such as in the center of
Trenton, NJ.
Phytoremediation can start as
a garden
U.S. EPA’s mission:
1. Protect human health
2. Protect the environment
The US EPT use 9 criteria to evaluate the alternatives
and determine the remedy preference
1.
2.
3.
4.
5.
6.
7.
8.
9.
Overall protection of human health and the
environment
Compliance with applicable or relevant and
appropriate requirements
Long-term effectiveness and permanence
Reduction of contaminant toxicity, mobility, or
volume through treatment.
Short-term effectiveness
Implementability
Cost
State acceptance
Community acceptance
In a Superfund site, it is the task of the
US EPA RPM (remedial project
manager) to choose a remedy and write
the record of decision (ROD) for the site
For the RPM to consider phytoremediation, at least
three different assurances must be in place for
final remedy selection:
1. Adequate containment of contaminated soils,
groundwater, and sediments must be assured until the
plants associated with phytoremediation have
established themselves at the site to a point that they are
either containing or degrading the contaminants of
interests.
2. An adequate backup technology with a high chance of
success must be ready and available to use at the site.
3. Evidence of the effectiveness of phytoremediation that is
specific to the site matrix and contaminants must be
presented.