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Phytoremediation
Principles and studies done at
Overview Processes
Processes summary
Change of water balance (2/3rd transpired)
Change of soil conditions (Redox, pH)
Root zone degradation (100times more bacteria)
Uptake into plants (water soluble compounds)
Metabolism by plants (?)
Toxicity to plants (?)
Definition:
Phytoremediation = healing of soils with plants
Engineer!
Phytoextraction
Rhizo- and phytodegradation
Hydraulic control
”Pump and tree”
Phytovolatilization
Phytoremediation Techniques Phytoremediation projects at DTU
- Tankstation Axelved (1999, gasoline)
- Asphalt work Vassingerød (1999, PAH)
- Gas works Søllerød (2000, cyanide)
- ENDEGRADE (2001-2004, toluene)
- Harbour sludge Antwerp (2003-2004, TBT)
- Kalvebod Miljøcenter (2005- 2006, copper, PAH)
- Airport Szprotava (kerosin) 2014
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General conclusions from field tests
+ Phytoremediation is helpful,
but not a „wonder weapon“
- - - Time scale is very long (> 10 years)
if something happens at all!
+++ The method is very cheap
(~5% of conventional costs)
-- - Engineering companies don‘t like it
(nothing to earn)
--- Take care! some engineers promise too much
++ Many abandoned sites might be used for
biofuel production, as parks ...
Experiments & Real Life at DTU
The Challenge
Phytoremediation has a good reputation (green, cheap, in situ).
The processes at site are very complex and difficult to predict.
Does it work?
and if so, why?
Toxicity test
soil or solution
Metabolism
closed bottle
Mass balance
model Mass balance
experiment
Toxicity
very toxic to
trees?
Kinetics
Michaelis-
Menten?
Monod?
Calculation
Mass
balance
Experiment
Mass
balance
Test bacterial
metabolism
yes
no
none
Test scheme phytoremediation
no
phyto-
remediation no
degradation
Acute toxicity test with trees Principle: healthy trees transpire more
Loss of weight compared to controls
fast, cheap, reliable
3
Toxicity of KCN to willow trees
in hydroponic solution in sand
(toxic at > 5 mg/L) (toxic at > 20 mg/L)
% T
ran
sp
irati
on
Toxic at
< 1 mg/L ?
yes
no
Willow tree acute toxity test
Results in water // in soil
KCN, KCN, PAH, BTX, Cd
3,5-dichlorophenol, detergents
Toxic at
< 100 mg/L ?
yes
no
MTBE, phenol,
Nano-TiO2,
antibiotics
diesel, gasoline,
TBT, PAH, FeCN
2,4-D
Cu
TBT
Closed-bottle test for metabolism
2 grams leaves, roots or stem in 100 ml solution
Concentration tracked by chemical analysis here done by Morten Larsen, Ex-PhD, now COWI
Degradation kinetics bacteria and trees
MTBE, PCB
Michaelis-
Menten
Monod
none
Plants
Bacteria
HCN, FeCN
chlorobenzoic acid
BTX, phenol
(TBT, oil, PAH,
detergents, Cl-phenol)
and many more …
Plants are usually bad degraders. Bacteria needed.
Idea: Symbiosis
Plants transport bacteria sitting on
roots down to deep soil and distribute
them. Plants suck the polluted water
towards root-colonizing bacteria.
Bacteria grow and degrade pollution.
And protect plants.
Test in laboratory and practical
application outside.
Bacteria can either be added (dip roots
into a suspension with cells) or develop
naturally.
For shallow contamination only.
How can we bring plants and bacteria together?
4
Test of concept: protection of lupin by endophytic bacteria
(Barac et al.)
Toluene in
water Bacterial
degrader
added
Ford Genk: BTEX from fuel and solvents in groundwater
275 poplar trees planted in 1999 to stop the shallow BTEX plume.
Monitoring for 6 years. Tree roots and associated bacterial
community degraded toluene. After remediation, bacteria died off.
Monitoring of
Remediation Ford Genk
Plume after
13 month (A)
42 month (B)
50 month (C)
55 month (D)
Field study TIMBRE project
"wild" phytorem at the former Russian airport Szprotawa in
Poland - jet fuel and BTEX
Lauge PW Clausen, Stephan Bartke, Mariusz Kalisz, Janusz
Krupanek, Eugen Martac, Nicolas Fatin-Rouge, Mette Algreen and
Stefan Trapp
Department of Environmental Engineering DTU (DK), Helmholtz
Centre for Environmental Research – UFZ (D), Institute for Ecology of
Industrial Areas (PL), Fuegro (D), Université de Franche-Comte (F)
Regeneration of a brownfield mega-site –
Review of technologies available for a former
military airport Table of Contents
1 Historical evaluation
2 Site characterisation
3 Clean-up technologies
5
History The site we deal with is a former Sowjet military airport (nuclear) in
Silesia/Poland in use until 1992. The Russians voluntarily retreated and
left an abandoned airfield.
26
TIMBRE test site: Szprotawa, Poland
Former Soviet airbase
200 ha
Site Impressions
Fueling of a Mig 29
Main pollution at Szprotawa airport is from jet fuel
What is jet fuel?
"Most aviation fuels available for aircraft are kinds of petroleum
spirit, petroleum ether, also known as benzine, naphtha".
Petroleum ether is a mixture of light alkanes, e.g., pentane,
hexane, and heptane.
Historical Evaluation Site characterisation tools
Geological profiles
Contaminants in groundwater
Soil gas
Risk assessment
Tree core sampling
Contaminants in soil
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Spatial distribution
more to site characterization please see poster Mette Algreen
Highest pollution at the fuel station - a 200 tons kerosin NAPL (80 000 m3)
+ wide diffuse pollution near the air field (engine heating)
What to do ?
III Remediation options
Experience from the past: Airport Hradcany (CZ)
Former Russian military airport contaminated with kerosin etc.
Remediation by Kap = Earth Tech = Aecom since 20 years
Hradcany remediation: combination of several methods
I. stage
– Soil vapour extraction + dual phase extraction – removal of
extractable oil phase
– 1 – 2 years in the source zone
II.stage
– In situ aerobic biodegradation with oxygenation and
nutrient supply for 6 years (bioventing/biosparging)
– > 90 % of hydrocarbon removal
Evaluation of options for Szprotawa remediation
Approach Considered technologies Criteria of evaluation
time costs sustainability
Quick remediation
(based on ex-situ techniques)
Polluted soil replacement, eventual on-site soil remediation.
Supporting techniques could be needed (ISCO)
+ + + - - - - - -
SHORT-term remediation
ISCO based techniques - + + - - + - - +
LONG-term remediation
Bioremediation combined with ISCO techniques,
enhanced bioremediation.
- - + - - + - + +
Soil vapour extraction, and/or bioventing
- + + - + + + + +
Phytoremediation supported by humification, lime treatment (land farming)
- - - + + + + + +
Suspended usage
MNA, phytoremediation/ forestation, continuous risk control
- - - + + + + + +
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Cheap Solutions I
CO2 Methane
Soil gas indicates ongoing natural attenuation
Cheap solutions II
Trees remove VOC and aerate soil - stimulate natural
oxidation with trees?
Remediation options
Vapour extraction and bioventing are two proven successful
methods, only neither cheap nor fast.
Alternatives
"Slurping" (sucking of free phase)
ISCO in situ chemical oxidation (of the source zone)
Natural attenuation (of the diffuse pollution)
Phytoremediation (of the diffuse zone)
Decision to be made in Poland
Questions?
Field Study: Full-Scale Phytoremediation Project
Gas Works Holte
Holte / Søllerød (near Holte Midpunkt)
Pollution from old gas works (tar and PAH; cyanide)
In the 1990ies, CN was found in drinking water wells in 60
m depth
Cyanide (Blåsyr)
Free cyanide (HCN, CN-) is
extremely toxic
World production is
1.4 mio tons/year
Environmental sources are
- Gas works waste (iron CN)
- Gold mine effluents (free CN)
- Chemical industry (Bhopal)
- Others
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Søllerød gasworks site (1955) The problem at former gas works
is the waste from
gas cleaning.
It contains 1- 20 g CN/kg
and was dumped at site …
Cyanide is iron complexed
(Prussian blue).
This is a solid (blue powder)!
Geochemistry of FeCN
start
here
The waste persists for decades and decomposes to
… HCN
250 000 tons alone in Denmark!
Frequently, gas works were close to water works
... and iron cyanide leaches into wells
Map of Contamination Holte gas works
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Remember: Trees take
up HCN and FeCN and
degrade it to harmless
amino-acids.
In vivo HCN metabolism by willows
Metabolism pathway of cyanide (HCN) by plants
Metabolism kinetics by plant enzymes
where
v (mg/d) is the removal velocity of
substrate with concentration C (mg/L),
vmax (mg/kg/d) is the maximal removal velocity,
KM (mg/L) is the half-saturation constant and
M (kg) is the mass of the plant.
MCK
Cvv
dt
dm
M
max
Michaelis-Menten kinetics
Michaelis-Menten enzyme kinetics
CK
Cv
dt
dC
M max
maxvdt
dCKC M C
K
v
dt
dCKC
M
M max
"zero order", linear "first order", exponential
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6
Time (d)
Sub
str
ate
C (
mg
/l)
0
2
4
6
8
10
12
0 2 4 6
Time (d)
Sub
str
ate
C (
mg
/l)
low C high C
Michaelis-Menten parameters
vmax
mg/kg/h
KM
mg/L
Roots 6.9 0.44
Leaves 9.6 0.59
Results for HCN and willows
10 mg per kg plant and hour is 50 kg per ton plant and year
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Michaelis - Menten in the mass balance
Steady-state gives a non-linear
(quadratic) equation
with two solutions
RM
RRR
RWR
W
R
R
CK
CvCk
KM
QC
M
Q
dt
dC
max
02 cbCaC
inflow to roots outflow from roots metabolism
Example calculation (cyanide, willow trees, with metabolism)
The relation between external concentration and
concentration in roots is non-linear !
0
10
20
30
40
50
0 20 40 60 80
CW (mg/L)
Cro
ot
(mg
/kg
)
metabolism
= uptake metabolism
< uptake
toxic effects
Model versus Experiment
Trees dead
Trees metabolize HCN – or they die!
6000 trees were planted at the former gas
works site - and survived!
Gas works Holte 2002 and 2005
rapid growth of poplars
2002 2005
Holte 2005/6
Remediation and public park at the same time
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Holte 2007
Trees have grown up to 15 m
Søllerød 2000 - 2010
Trees pump off contaminated water
year L / m2/
year
2001 12
2002 82
2003 217
2004 267
after 2004 267
> 40% of the rain is
pumped off by trees
Cost efficiency
Traditional remediation: about 40 mio DKr
> 50% for pumping of polluted groundwater
Phytoremediation:
about 50% cheaper (savings for pumping)
Søllerød
2000 2002
Measured concentration of CN in leachate
source: L.C. Larsen, ATV-meeting DTU 2005
Total CN (mg/l) in GW < 15 m depth, together with success criteria
Source: documentation report Orbicon
CN in water < 15 m depth
Total CN (mg/l) in GW > 15 m depth Well B97.16 is in the center of contamination
CN in water > 15 m depth
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Geochemistry of FeCN
slow dissolution of solid complexed CN Prussian blue
start
here
1955
2001
Summary Results Gasworks Holte
• The primary goal was reached (no more CN in well water)
• The target for the upper aquifer wasn’t met.
• Costs were reduced (50%)
• It took long (> 4-5 years) before concentrations of CN in GW
fell (close to ) the success criteria
• There were no particular difficulties (accidents etc.)
BUT
• The source of pollution (solid iron cyanide) is still there
• The problem holders are not satisfied, not at all.
Any questions?