lecture 2 ghoshal
TRANSCRIPT
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Management and remediation ofsites for extractive industries
Subhasis GhoshalDepartment of Civil Engineering
McGill University, Canada
Universidad ORT Uruguay, Montevideo , Apri l 4-8, 2016
Organizer: Prof. Lorena Betancour, Universidad ORT Uruguay
Pump-and-Treat Remediation
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• Wide use since 1980s – 75% of Superfund sites
• 1990’s: ability to achieve complete aquifer restoration?
– Slow decrease in contaminant concentrations, tailing
and rebound
Pump and Treat Remediation
Technology Objectives
• Objective of technology
– Hydraulic containment using pumping wells (& to a lesserextent: subsurface drains, trenches and barrier walls
– Treatment of contaminated water
• Prerequisites
– thorough site characterization• Contaminant types and distribution
• Hydrogeology
– Source removal (excavation, pumping of NAPL)?
• Treatment objectives – realistic goals needed
– For high degree of clean-up: homogeneous and permeablestrata in aquifers, no NAPL contamination, non-sorbingcontaminants
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• Tailing: progressively slower rate of decline incontaminant concentrations
• Rebound: rapid increase in contaminantconcentrations after pumping has stopped
The Clean-up Challenge: Tailing and Rebound
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• Effect of Tailing and Rebound on Remediation
– Longer treatment times
– Residual concentration in excess of cleanupstandard
• Contributing factors
– Slow release of solutes from NAPLs
– Slow contaminant desorption
– Slow precipitate dissolution (for heavy metals)
– Slow diffusion of compounds from clay layers
and lenses
Tailing and Rebound
Factors contributing to tailing:Effect of mass transfer from source (sorbed phase,
NAPL or diffusion limited zone)
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Factors contributing to tailing:
Effect of clay layer thickness and
Factors contributing to tailing:Effect of geological stratification
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• Hydraulic containment: to prevent further
spreading of plume
– Extraction wells create capture zones
Capture Zones
Equipotential Lines Groundwater
Flow Lines
PW = pumping well
Capture Zones
Groundwater flow
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Placement of well with respect to
plume size
• Optimizing Design and Operation
– Pulsed pumping
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• Variations and Alternatives
– Horizontal and inclined wells
Intercepting Fractures
Accessing Beneath Structures
• Surfactants (SURFace ACTive agents)
Enhancements to Pump and Treat
CMC
Micelle
Surfactant concentration
Critical Micellar Concentration (CMC)
NAPL
Water
Monomer
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• Surfactants (SURFace ACTive agents)
Enhancements to Pump and Treat
Aqueous Phase
NAPL Phase
Surfactant Micelle
Solubilizationrelated to Kow
• Surfactants (SURFace ACTive agents)
Enhancements to Pump and Treat
C i , t o t a l
Ci, micellar
CMC
Surfactant Concentration, Csurf (moles/L)
S o l u t e
C o n c e n t r a t i o n ( m o l e s / L )
Ci, aqueous
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• Soil Flushing
Enhancements to Pump and Treat
c k g h N l
ρ σ
∆ = ∆
Iron-Nanoparticles for
groundwater remediaion
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Groundwater Contamination by
Chlorinated Solvents
• Trichloroethylene,perchloroethylene
• Carcinogenic, neurotoxic
• Restoration of groundwaterto meet drinking water
standards have not been
successful
• ~1 million Kg of chlorinated
solvents improperlydischarged into ground in
U.S & Canada
SolventRelease
PollutantPlume
Water WellSolvent
Why Nano Fe(0)?• Very High Reactivity
– Niche applications forreducible pollutants
(chlorinated organics, heavy
metals, nitrates, radioactive
waste, PCBs)
– Rapid in situ treatment ofgroundwater contamination
• Low cost and commerciallyavailable
• Toxicity?
Chlorinatedorganics
Heavy metals
Core-shell structure of nanoscalezero valent iron (NZVI) particles
Theron et al., 2008
Fe203
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Nanoscale Zero Valent Iron
23
Bioremediation vs remediation with Fe0
24
Roberts et al., 1996
Arnold et al., 2005
Reactions with Fe0
Only Dehalococcoides - Capable ofcomplete dechlorination to ethene
Biodegradation Reactions
Biodegradation
Reactions with Fe0
Stable reaction products areacetylene, ethene, ethane
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nZVI-based
in situ remediation
Contaminated Plume
Injection of nZVI-slurry
Source
Decontaminated Zone
Groundwater flow direction
nZVI and pollutantreaction
Water table
Fe
Iron oxides andhydroxydes
R Cl
R H
+ Cl-
+ H+Direct int roduct ion of n ZVI into the environm ent
Contaminated Plume
Injection of nZVI-slurry
Contaminant Source
Decontaminated Zone
Groundwater flow direction
Water table
nZVI-based in situ remediation
Polymer
-nZVILimited transport of bare nZVI
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Iron Nanoparticle Aggregation &
Effects of Polyelectrolyte Coating
Electostatic repulsion force
Magnetic attraction forces
Electostatic + steric repulsion force
Polymer Coating:CarboxymethylCellulose (CMC)
Magnetic attraction forces
Bare-nano Iron
accumulationIn a sand packed
column
Polymer
stabilized
nano-iron
distribution in
a sand packed
column
Mobility enhancement:
polymer coated nZVI
• Causes for enhanced mobility:
– Reduced aggregation of nZVI due to charge and stericstabilization
– dispersed particles
– reduced deposition and filtration of nZVI in porousmedia
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Polymer-Coated NZVI
FeSO4 + NaBH4 + stabilizer H2O Fe + sulfate and boronic salts
Cirtiu, Raychoudhury, Ghoshal, Moores.
Colloids and Surfaces A: Physicochem. Eng. Aspects 390 (2011) 95– 104
• Carboxymethyl cellulose: very efficient in colloidally stabilizing particles
• Synthesized particle size different for the different polymers• All polyelectrolytes showed binding to the Fe(0)/FeOOH surface.
Bottom-up synthesis of CMC-NZVI
FeSO4 + NaBH4 + stabilizer H2O Fe + sulfate and boronic salts
Carboxymethyl cellulose (CMC)
stabilizer
5 g/L CMC, 1 g/L Fe→ 5 nm avg dia.5 g/L CMC, 2 g/L Fe→ 75 nm avg dia.
600 900 12001500 18002100 24002700 30003300 36003900
asymCOO
-
symCOO
-
CMC-ZVI CMC
T r a n s m i t t a n c e
( % )
Wavenumber (cm-1)
FTIR spectrum of CMC-ZVI
R
CO O
Fe Fe
Bidentate bridginginteraction
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NZVI Transport Fundamentals
Column Transport experiments
Syringepump
Inlet; Co= 70 mg/L-725 mg/L
Outlet; C
sampler
Sand size (dc)= 450µm(F3050)Particle size (dp)=5.5nm-75nm
L=9 cm; D=1 cmFlow = 0.45 cm/minIS=0.1mM-10mM
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CMC-nZVI Transport in Packed Columns
Pore volume =V*t/(L*n)
n=porosity , V=velocity
Pore volume (PV)
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
C / C
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
C0=0.725 gL-1
Tracer KNO3
Simulated C/C0
(without aggregation)
Outlet concentration = C(changes with time t)
L=columnlength
Inlet concentration = Co(constant at all time t)
CLASSICAL COLLOID DEPOSITION MECHANISMS IN
POROUS MEDIA
Single collector efficiency: Probability
of collision between particle-sand
(i) Diffusion
(ii) Interception
(iii) Sedimentation
Attachment efficiency: Probability of
sticking on sand surface after collision
(i) Solution chemistry
(ii) Surface charge
34
Diffusion
Interception
Sedimentation
Collector
Colloid
F l o w d i
r e c t i o n
o
cd
vnk αη
2
)1(3 −=
Attachment
efficiency Single collector
efficiency
k=deposition rate coefficient, n=porosity,
v=interstitial velocity, dc=average sand size
kC x
C v
x
C D
t
C x −
∂
∂−
∂
∂=
∂
∂2
2
Dispersion
coefficient
Pore water
velocity
Deposition rate
constant
Particle diameter
dependent
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Particle size (nm)
100 200 300 400 500 600 700 S i n g l e c o
l l e c t o r c o n t a c t e f f i c i e n c y ( η
0 )
0.01
0.02
0.03
0.04
0.05
0.06
aSingle collector efficiency (η0)with different particle size (dp)
Single-Collector Contact Efficiency
36
CMC-nZVI deposition in granular porous media
Collector
s e d i m e n t a t i o n
Influent
Effluent
EffluentInfluent
Particle-collectorattachment
Influent PSDEffluent PSD
C o n c e n t r a t i o n
Particle size(dp)
C o n c e n t r a t i o n
Particle size(dp)
Particle-particleattachment
t=t0
t=tend
t=t0
t=tend
Flow path 2
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CMC-nZVI Transport:Effect of Particle Concentration
Accounting for detachment of deposited particlesprovides reasonable fits
Pore volume (PV)
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
C / C
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
C0=0.07gL-1
C0=0.2gL-1
C0=0.725gL-1
Fitted Curve
b
ε
ρ depn
i
iidep
S k t C k
x
C v
x
C D
t
C det
1
,2)(
2
+−∂
∂−
∂
∂=
∂
∂
=
Adhesive torque
(Tadhesive) due to DLVO
interaction energy
Torque (Tapplied) due to
hydrodynamic dragSand
grain
Tapplied /Tadhesive>1 suggestspossibility of detachment
NZVI Reactivity
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NZVI Reactivity to TCE
Reactions under Iron Excess Conditions
Liu et al., 2005. Environ.Sci. Technol.
42
Solutions:
Surface functionalization
Fe0
S2-
Carbon supportDoping with
metal (Pd)
Addition of
inorganic ions
Oxide passivation
layer
Fe0
• NZVI reacts with water andoxygen, forms oxide layer:
Fe3O4/FeOOH
• Thick oxide layers hinderselectron transport
The Problem:
Surface passivation
Fe(0) + 2H2O→ Fe(OH)2 + H2
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NZVI reactivity
Bimetallic
nanoparticles
Many folds
increase
in reactivity with
Pd,
but……..Pdcontributes
to toxicity
Yan et al. 2012
Yan et al 2010
Oxide passivationlayer
Aged, passivated nZVI
TCE degradation kinetics
Initial TCE Concentration 30mg/L
NZVI concentration 2.0 g/L
NZVI-Pd 0.1 g/L (0.5% wt/wt of Pd) 44
Time (hr)
0 2 4 6 8 10 12 14 16
C / C 0
0.0
0.2
0.4
0.6
0.8
1.0
No NZVI
NZVI only
NZVI-Pd
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Sulfidation of NZVI
Rajajayavel and Ghoshal, Water Research, 2015, In pressTime (days)
0 5 10 15 20 25 30
H y d r o g e n ( m M )
0
20
40
60
80
100
120
bare NZVI
Sulfidated NZVI
33 % less loss ofelectrons to water:
Sulfidated-NZVIthus more long-
lasting
TCE degradation kinetics with sulfide functionalized NZVI
Initial TCE Concentration 30mg/L
NZVI concentration 2.0 g/L
NZVI-Pd 0.1 g/L (0.5% wt/wt of Pd)
Time (hr)
0 2 4 6 8 10 12 14 16
C / C 0
0.0
0.2
0.4
0.6
0.8
1.0
No NZVI
NZVI only
0.7 mM Sulfide
1.0 mM Sulfide1.6 mM Sulfide
2.4 mM Sulfide
3.1 mM SulfideNZVI-Pd
• k obs (h-1) for sulfide
amended NZVI > k obs forbare NZVI by up to ~40times.
• TCE is primarily degraded toethene and acetylene.
• Coating NZVI withcarboxymethyl cellulose(polyelectrolyte) results inidentical reactivity as bareNZVI with sulfide
46
Rajajayavel and Ghoshal, Water Research, 2015, 78:144-153
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Case Studies
48
Emulsified NZVI
Geosyntec consultants, NASA
• NZVI particles emplaced within asurfactant-stabilized, biodegradable, water-in-oil emulsion.
• Oil membrane is hydrophobic and misciblewith DNAPL.
• Biodegradation enhanced by vegetable oiland surfactant components of EZVI.
Brooks, 2000
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TCE Contaminated Site
- NASA Rocket Launching Pad
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Case study – Emulsified NZVI
53Pre-Demonstration (March 2002) Post-Demonstration (Nov 2002)
EZVI treatment: TCE Degradation Products
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Theoretical Cost of Treatment using NZVI
ForAcetylene, n=4Ethene, n=6Ethane, n=8
Minimum: 4e- or 2Fe0 / TCEor: 0.85:1 (by mass)
Assuming $50/Kg Fe0:$44/Kg TCE (acetylene)
$66/Kg TCE (Ethene)$88/Kg TCE (Ethane)
Fe0 delivery to all TCE molecules?
Permeable Reactive Barriers
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Permeable Reactive Fe(0) Barrier
Permeable Reactive Barrier Walls
• In-situ remediation for chlorinatedhydrocarbons & heavy metals
• Usually contain iron or other zero-valentmetals
• Hydraulic retention time is key
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Reactive Barrier Walls
1) funnel and gate
2) continuous trench
Case Study
• Elizabeth City, NC
• Contamination of groundwater with Cr(VI) and TCE(overlapping plumes)
– TCE (20 000 ug/L), cDCE and VC: degreasing operations
– Cr (10 mg/L in groundwater, 14,500 mg/Kg in soil):electroplating operations
• Permeable reactive barrier
– Continuous wall configuration: 46 mX 7.3m X 0.6m – granular iron: reactive medium
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Cr(VI) reduction by Fe0
From Gould (1982)
A = surface area of zero-valent Fe (cm2/L)
k = 5.45X10-5 L/cm2.min
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TCE transformation
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PRB Case Study
• Cost Comparison with Pump and Treat
Reactive Wall Pump and Treat
Installation $500 000 $500 000
Monitoring $32 000/yr $32 000/yr
Maintenance $0 $200 000/yr
Equipment $0 $500 000/20 yrs
Savings = $ 4.5 million/20 yrs
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Bioremediation
• Bioremediation: Engineered or natural process inwhich biological reactions break up or transformpollutant compounds, thereby remedying oreliminating environmental contamination
• Mineralization: Conversion of an organic moleculeinto its inorganic constituents (e.g., CO2, NO3
-, SO42-,
PO43-)
• Biodegradation: A subset of biotransformation
which causes simplification of an organic compoundsstructure by breaking intermolecular bonds
Bioremediation
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• To obtain energy for growth and maintenance
– Electron transfer (redox) reactions provide energyand result in biodegradation
– Microbially-mediated redox reactions involve
• electron donor (usually: organic matter /organicpollutant)
• electron acceptor (usually: oxygen, nitrate,
sulfate, CO2)• As a source of C for building cell materials
Why do microbes degrade organiccompounds?
80
Fundamentals of Bioremediation
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• BTEX, PAHs – aerobic & anaerobic biodegradation
• Chlorinated hydrocarbons
– Aerobic biodegradation (pollutant acts as electrondonor and O2 acts as electron acceptor) – DCE
– reductive dehalogenation (pollutant acts aselectron acceptor, occurs under sulfate reducingand methanogenic conditions) – PCE,TCE, DCE,TCA
– Cometabolic biodegradation (e.g., toluene:primary substrate, TCE cometabolic substrate)
Biodegradation of Common Pollutants
– Near ground surface, O2 available in abundance
– If BOD of contaminant zone >> dissolved O2, thenonly anaerobic biodegradation feasible
– Deep in subsurface, no O2 but naturally abundantnitrate, sulfate to sustain anaerobic biodegradation
Where do electron acceptors come from?
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Volatilization
Aerobic Unsaturated Zone
Oxygen Exchange
Aerobicuncontaminatedgroundwater
Dissolution
Aerobic Processes
Anaerobic core
Mixing, Dilution
Advection
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86
Anaerobic degradation of chlorinated
organics by Dehalococcoides .,These are the only group of microbes that are capable ofcomplete dechlorination of chlorinated solvents.
Dehalococcoides sp.,http://www.beem.utoronto.ca/research/67
Dhc ., are not ubiquitous and often are present in low
numbers. (Hendrickson et al., 2002)
Strict anaerobes that require anoxia and reducing
conditions for growth.
Difficult to grow as pure culture.
Enriched with mixed culture consortia of bacteria
(Methanogens, Acteogens, Sporumosa...)
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87
Dehalococcoides work in consortium with other
bacteria
Carbon source
Electron donor pH Temperature nutrient availability
Growth Factors
88
SIREM KB-1®
A Case study KB-1 ® is the commercial name for mixed culture
dechlorinating bacteria.
It is the most widely used bio-augmentationculture in the world.
Ref: http://www.siremlab.com/products/kb-1
Site history
Portland, Oregon
TCE released during 1980’s TCE and cDCE ~ 592 mg/L and 92 mg/L 50 to 110 feet below ground surface
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KB-1® A Case study The full scale implementation consisted of a 150 footlong bio-barrier amended with an electron donorand KB-1®.
Approximately 200 injection points were used toinject 270,000 kilograms of electron donor and 2,000liters (L) of KB-1®.
The site was continuously monitored for itperformance.
“TCE concentrations were below federal MCLs (5 µg/L) in 6 months”
TCE dechlorination products (cDCE and VC) were generated initially,
followed by a rapid decline with observed increases in ethene.
http://www.sirem-lab.com/images/PDF/case-study-maulfoster.pdf
• Other than electron acceptors, N, P, what otherconditions are required?
– pH: 6-8, adequate buffering capacity
– Temperature: subsurface ground temperatureusually ideal but if less than 5oC, usually lowbiodegradation rates
– Moisture > 40%
– Absence of toxic agents, e.g., high conc. of heavymetals
Bioremediation Requirements
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Bacterial Metabolic Genes
GENEPLASMID/
CHROMOSOMEENCODED
POLLUTANT STRAIN
a l k Plasmid (OCT) alkanes
(C6-C10) Ps e u d om o n a s pu t id a
b p h Chromosome PCBs A l ca l i g en es
e u tr o p h u s H850
n a h Plasmid (pKA1)
naphthalene,
anthracene,
phenanthrene
Pse u d om o n as
f l u or esce n s 5R
p h l Chromosome phenol A l ca l i g en es e u t r op h u s JMP134
x y l Plasmid (TOL) xylene,
toluene
Ps e u d om on as p u t id a
mt-2
Biodegradation Kinetics
Cell growth rate: X dt
dX µ =
Monod’s Kinetics:C K
C m+
= µ
Substrate degradation kinetics:
( )C K Y
CX
dt
dC m
+
−=
X = cell concentration (mg cells/L) = specific growth rate (day-1)
Ks = half saturation constant (mg/L) m = maximum specific growth rate (day-1)
C = substrate concentration (mg/L) Y = yield coefficient (mg cells/mg substrate)
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• Permeable Biobarriers
In-Situ Bioremediation
Bioavailability
water
NAPL
solid
Contaminated soil matrix
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• Can contaminants sorbed on to soil or present inNAPLs be biodegraded?
– Conventional theory: only dissolvedcontaminants are degraded by bacteria -----‘bioavailability’
– Once dissolved phase contaminants are depletedby biodegradation, sorbed or NAPL contaminantswill desorb/dissolve in response to the decrease inaqueous phase concentration and thereafter
biodegrade
Bioremediation
Limited Bioavailability
• Low aqueous solubility of HOCs
• Entrapment in micropores
• Strong binding (sequestration) to soil organic matterwith aging
• conventional analytical techniques inadequate forpredicting bioavailability
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Limited Bioavailability
• Desorption/dissolution rates may influencebiodegradation rates
• Overall biodegradation rates can be influenced byrates of desorption/dissolution or intrinsic rate ofmicrobial uptake
• Desorption/dissolution is often found to be the ratecontrolling phenomena
Mass Transfer and Biodegradation Processes at the
Particle Scale
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Identifying Rate Controlling Phenomena
Bi >1 Bi 1φ>1
Diffusion control Biokinetic control Dissolution control
Da
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• Enhanced Pump and Treat
In-Situ Bioremediation
• Bioventing
In-Situ Bioremediation
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• Air Sparging
In-Situ Bioremediation
• Intrinsic Bioremediation and Natural Attenuation
In-Situ Bioremediation
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How do you prove that bioremediation isoccurring in-situ?
• How to distinguish between biotic and abioticprocesses?
• Difficulty of performing mass balances in the field
How do you prove that bioremediation is
occurring in-situ?
Direct measurements
– Increase in number of bacteria (especially pollutantdegrading bacteria)
– Compare bacterial adaptation before and duringbioremediation
– Decrease in electron acceptor concentrations
– Formation of by-products
– Ratio of biodegradable to non-biodegradablecomponents
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How do you prove that bioremediation isoccurring in-situ?
Experiments in the field
– Stimulating bacteria within subsites to test forincreased contaminant losses
– Monitoring conservative tracers to assess abioticlosses
– Radio-labelling contaminants to determine the fateof carbon
How do you prove that bioremediation is
occurring in-situ?
Modelling experiments
– To represent abiotic loss mechanisms
– To estimate biodegradation rate
– Compared to actual losses in the field
Need more than one piece of evidence needed toprove biodegradation in the field
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Ex-situ Bioremediation
• Slurry phase treatment (Bioreactors) – Rate-limiting step?
• Rate of desorption/dissolution process
• Rate of microbial uptake (biodegradationkinetics)
( )t eqdC A
K C C dt V
= −
water
NAPL
solid
Ex-situ Bioremediation
• Landfarming
– Aeration and mixing
– Microbial seed
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Ex-situ Bioremediation
• Biopiles
– above-ground, engineered composting systemsused for the treatment of contaminated soils
impermeable base
bermberm
contaminated
soil
protective
membrane
leachate
collection
pipe
monitoring
devices nutrient and
water addition
water knockout tank
blower
Biopiles• Soil preparation includes
• screening, crushing, mixing, adding bulking agents
• pH adjustment
• enhancement of indigenous microbes
• Design elements
– Protective membrane
– Impermeable base
– Aeration + air filtration
– Moisture + nutrient addition
– Leachate collection system
– Temperature
– Monitoring
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Biopiles under Construction
Impermeable Liner
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• Applicability
– Mainly for petroleum products
– Lighter, volatile hydrocarbons removed throughaeration
– Medium to heavy hydrocarbons biodegraded
– Less effective for chlorinated hydrocarbons thatare degraded anaerobically
Biopiles