ESM 223
Phytoremediation
In Situ Processes
Phytoremediation
& Vitrification
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Phytoremediation Phytoremediation
Phytoremediation is the use of plants to treat Fast-growing trees and aquatic plants have been used
to treat high nutrient content in wastewaters
contaminated soil or ground water Advantages:
Proposed for organic and inorganic pollutants low-cost (capital and operation)
Most of the activity is in the root zone aesthetic
soil stabilization
Differentiate between:
reduced leaching of pollutants
Phytostabilization: use the plants to stabilize soil
Limitations
to avoid erosion and thus reduce risk of only treat root zone
exposure high pollutant concentrations may be toxic to plants
Phytoextraction: remove the pollutants from the species specific => pilot study
subsurface into the above-ground plant portions
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Phytoremediation Phytoremediation
Mechanisms:
Direct uptake:
Only useful for organics with low Kow (~
0.5 to 3), i.e. moderately hydrophobic
Capillary action pulls in the contaminants
Once in the plant, the pollutant can be
accumulated, metabolized (used in
respiration) or lost through volatilization at
leaves
Specific enzymes needed to metabolize
the pollutants (used to design modern
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Phytoremediation Phytoremediation
Degradation in Rhizosphere: Phytoextraction of heavy metals:
Rhizosphere has high microbial content, plus Some plants can accumulate high
exuded enzymes from plants and microbes concentrations of metals (2-5%) in their
Plants also exude sugars, carbohydrates and biomass
amino acids which promote the formation of a Hyperaccumulator plants can translocate the
healthy microbial and fungi population metals to their leaf and stalk biomass, with
Degradation of organics (BTEX, hydrocarbons, concentrations about 100 times greater than
PAHs, chlorinated) is promoted in this region non-accumulating species
through enzymatic activity The plants or leaves can be harvested for
disposal of the metals
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Phytoremediation Phytoremediation
Phytoextraction of heavy metals:
Indian mustard can accumulate lead at
rates of up to 2 ton/hectare, with 2 or
up to 3 harvests possible per year
Plants can only deal with contaminants
down to 24 in.
Poplars are being studied for removal
down to 10 ft - leaf litter may be blown
off-site...
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Phytoremediation Phytoremediation
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Phytovolatilization Phytovolatilization
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Phytoremediation Phytoremediation
Aquatic plants can accumulate metals and Poplars are popular for phytoremediation
other toxic substances directly from water due to their high growth rate, high
Attached algae have been shown to transpiration rates and deep roots
remove Cd, Zn, Ni and Cu Laboratory experiments at UW have shown
Some studies are looking at the removal of that poplars can remove TCE from soil by
radionuclides from water using aquatic direct uptake
plants Direct tracking of metabolites within poplars
Nitrates and other nitrogen compounds at was done to prove that uptake (and not
high concentrations can be removed either volatilization) was occurring - exposed for
from soils or groundwater months
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Phytoremediation Phytoremediation
As poplars grow, they extend their roots
towards the aerobic water table
can eventually affect GW flow around them
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Phytoremediation Phytoremediation
A hydrologic model (MODFLOW) was
used to determine how many trees had
to be planted to capture contaminated
water from a TCE spill
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Phytoremediation Phytoremediation
Planted area had to about 17 times
greater than source zone
consider geology and water table gradient
To increase water use from the
contaminated zone, cover soil with a
membrane and direct runoff off-site
Some irrigation is needed in first 3 years,
to achieve fast tree growth rates
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Phytoremediation Phytoremediation
TNT can be degraded by nitroreductase Municipal, subdivision and residential wastewater
and laccase enzymes, present in aquatic Glycol (Aircraft de-icing fluid)
plants Landfill leachate
Poplars and sycamores also contain Agricultural wastewater
nitroreductase and may be able to degrade
TNT Steel mill effluent
Parks and campground wastewater
Constructed wetlands may be used to treat
heavily contaminated soils at munitions Mine and industrial wastewater
factories Stormwater and surface water runoff
Current option is soil incineration (!) at a Contaminated soils and groundwater
cost of $400-1200 per ton Cellulose Processing
Domestic and industrial sludge
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Phytoremediation In-situ Vitrification
Apply electric heating to soils to achieve
very high temperatures
Temperatures achieved can be 1300-1600 oC
(2,400-2,900 oF )
Melt sand particles (forming glass)
Organics present are oxidized via pyrolysis
As glass cools, it immobilizes contaminants
heavy metals and radionuclides
4 electrodes are placed around “melt zone”
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In-situ Vitrification In-situ Vitrification
Vitrification can also be used for soils with
high PCB concentrations
“legacy” pesticides (DDT and other OCs)
Off-gases have to be collected, cooled and
treated (GAC) in these cases
Current treatment cost estimates for
The “technique” can be applied adjacent to a nonradioactive sites are in the range of
previous melt to form contiguous monolith $350-450/ton
Requires 0.7 to 1.1 kWh/kg of soil
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In-situ Stabilization In-situ Stabilization
Buried radioactive wastes at DOE sites
present a long-term problem Injecting grout into contaminated soil using a
cutting water “jet” and then supplying a low
Two options: viscosity grout which then solidifies
Excavate, treat (or re-treat) and re-dispose at a Grout materials are still being tested by DOE
well-engineered disposal site
and National Labs, but contain cements and
potential for worker exposure to waste,
airborne contamination via “friable” waste latex
salts Stabilized waste can be left in place with long-
long-term control requirements term monitoring
Stabilize waste in-situ to eliminate possibility of Stabilized waste can also be removed by
spread of contamination excavation
reduced exposure possibilities risk of exposure
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In-situ Stabilization In-situ Stabilization
Technology is still at developmental stage
grouting is a proven method
long-term effectiveness is still being studied
Estimated material costs are about $150 to
$400/m3 of soil treated
operating costs depend on treatment depth
Treatment rate (soil)
35-70 metric tons/hr at shallow depths
18-45 metric tons/hour at greater depth
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