Lecture 2 Ghoshal

8/17/2019 Lecture 2 Ghoshal

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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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Aqueous Phase

NAPL Phase

Surfactant Micelle

Solubilizationrelated to Kow



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


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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89

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


• Bioventing



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• Air Sparging


• Intrinsic Bioremediation and Natural Attenuation



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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


• Landfarming

– Aeration and mixing

– Microbial seed


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• 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

Lecture 2 Ghoshal

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