In Muddy Waters
Contaminated Sediments
R. Ravi Krishna
Department of Chemical Engineering
IIT- Madras
Image: Sediment Profiling Camera (http://www.vims.edu/bio/benthic/)
Sediments
Mineral Fraction –
Pore Water
Sand , Silt, Clays
Microbes
Organic and
Inorganic Phases
-
Sediments
Image Source: http://www.aquafact.ie/SPI2.html
Contaminated Sediments - Origin
Discharge Of Contaminants into Water
Contaminated Sediments - Origin
Direct Pollution of Water due to Discharge
Contaminated Sediments - Origin
Closure of Discharge – Water Pollution Still Present
Contaminated Sediments - Origin
Water Pollution due to release from accumulated
chemicals in the sediments
Chemical Release From Sediments
EVAPORATION
AIR
Resuspension due to
Turbulence
WATER
DIFFUSION
Bioturbation
Contaminated
bed source
SEDIMENT
UNCONTAMINATED
SEDIMENT BED
Chemical Release From Sediments
AIR
•
Some Chemicals of Concern
– Organic
• Polyaromatic Hydrocarbons (PAHs)
• Polychlorinated Biphenyls (PCBs)
WATER
– Toxic Metals
• Cd, Se, Cr, As, Hg, Pb
Contaminated
bed source
SEDIMENT
UNCONTAMINATED
SEDIMENT BED
Mobility - Parameters
•
Binding/Retardation of Chemical on
Substrate
– Nature of Contaminant Chemical
Surface Water
• Organic
–
–
–
Hydrophobic
Polar
Non-aqueous phase (oils)
• Inorganic
–
Oxidation State
– Nature of Substrate
•Equilibrium Thermodynamics
•Uptake
•Adsorption/Desorption
• Condensed – Organic/Inorganic
• Dispersed – Organic/Inorganic
•
•
Bioaccumulation and Biodegradation
Mass Transport
– Diffusion Coefficient
• Porous Media Characteristics
(Porosity/Tortuosity)
– Bioturbation
– Surface Mass Transfer Coefficient
– Advection
• Groundwater flow, Tidal Fluctuation
• Ebullition
Bed Sediment
Mobility - Parameters
•
Binding/Retardation of Chemical on
Substrate
– Nature of Contaminant Chemical
• Organic
–
–
–
Surface Water
Hydrophobic
Polar
Non-aqueous phase (oils)
• Inorganic
–
Oxidation State
– Nature of Substrate
• Condensed – Organic/Inorganic
• Dispersed – Organic/Inorganic
•
Bioaccumulation and Biodegradation
– Microbial Population
– Rates of Degradation
•
Mass Transport
– Diffusion Coefficient
• Porous Media Characteristics
(Porosity/Tortuosity)
– Bioturbation
– Surface Mass Transfer Coefficient
– Advection
• Groundwater flow, Tidal Fluctuation
• Ebullition
Bed Sediment
Mobility - Parameters
•
Binding/Retardation of Chemical on
Substrate
– Nature of Contaminant Chemical
• Organic
–
–
–
Hydrophobic
Polar
Non-aqueous phase (oils)
• Inorganic
–
Oxidation State
– Nature of Substrate
Surface Water
Bioturbation
Advection
Interfacial Mass Transfer
Diffusion
• Condensed – Organic/Inorganic
• Dispersed – Organic/Inorganic
•
Bioaccumulation and Biodegradation
– Microbial Population
– Rates of Degradation
•
Mass Transport
– Diffusion Coefficient
• Porous Media Characteristics
(Porosity/Tortuosity)
– Bioturbation
– Surface Mass Transfer Coefficient
– Advection
• Groundwater flow, Tidal Fluctuation
• Ebullition
Bed Sediment
Experimental Methods
• Binding/Retardation of Chemical on Substrate
– Physical and Chemical Characterization
• Extraction and Chemical Analysis
• Microscopic and spectroscopic analysis
– Adsorption/Desorption Isotherms
• Batch equilibration or Saturation column.
• Bioaccumulation and Biodegradation
– Batch Kinetics/Uptake/Toxicology Studies
• Mass Transport
– Effective Diffusivity Estimation
– Flux Measurements
Flux Measurement – Enclosed Samplers
• Measurement near sediment-water interface
– Benthic Flux Sampling Device
Flux Measurement – Enclosed Samplers
• Laboratory Microcosm with Sediment and
Surface Water Samples
Flux Measurement –
Time Series Concentration Gradient
• In-situ porewater samplers
– Membranes
– Probes
• In-situ Spectroscopic methods
– Laser Induced Fluorescence
• Sediment Cores
– Sectioning of thin layers
– Chemical Analysis
General Modeling Framework
• Overall Objective is to predict for Risk Assessment or
Remediation Design!!
• General Equation for 1-d transport of chemical within
sediment porewater (aqueous phase)
C
 2C
C
Rf
 Deff 2    K bio 
G
t
z
z
•
•
Rf - Retardation Factor
– εW+KPρb (KP = equilibrium partition constant, ρb = sediment bulk density)
Deff – Effective Diffusion Coefficient
–
•
•
•
•
DW.εW /τ (DW – diffusivity in water; εW – porosity; τ – tortuosity)
ν – advection velocity
Kbio – bioturbative transfer coefficient
G – rate of generation or degradation per unit volume
Initial Conditions: Spatial Concentration Profile of the sediment
Boundary Conditions:
– At sediment water interface: Mass Transfer into water – Depends on water flow regime,
topography of the sediment surface.
Assumptions: a) Local Equilibrium b) Uniformity of Parameters
Is it really that muddy?
• Estimated 3-12 million cubic yards of
contaminated sediments are managed
annually in the US.
– Several Superfund Sites in the US
– GE vs. USEPA over PCB contaminated
sediments in Hudson River
• Rhine River Valley in Europe
• International conference on sediment
remediation every 2 years.
Options for Remediation
• Monitored Natural Recovery
– Natural attenuation
– Least Expensive
• In-situ Capping
– Clean material cover over contaminated zone
– Motive is to allow undisturbed natural recovery
• Dredging
– Physical removal of contaminated material
– Relocation for storage/disposal/treatment
Monitored Natural Recovery
• Leave it Alone!! Let Nature take it’s
course.
– Biodegradation
• Based on native microbial population
• Modified microbial populations introduced
– Definition of a Sediment Quality Criteria
Sediment Quality Criteria
• Acceptable Sediment Contamination Levels (masschemical/mass-sediment).
• Based on “Bio-availability” of the chemical in the
pore water for processing by biological receptors.
– Toxicity of bio-available chemical concentration in
water.
• Traditionally, Bioavailability has been estimated by
assuming Equilibrium Partitioning.
Equilibrium Partition Constant (KP)–
For Organic Chemicals
CS
KP 
CW
Organic (hydrophobic) Chemicals Display
an affinity towards organic carbon in
sediments
K P  KOC  fOC
K OC
COC

CW
KOC – Index of Hydrophobicity
KOC is traditionally reported as
a normalized partition constant
for unresolved organic carbon
CS – Concentration of Chemical in Solids (g/g – dry basis)
CW – Concentration of Chemical in Pore water (g/L)
fOC – fractional organic carbon content (-)
Increasing
Hydrophobicity (KOC) or
Octanol/Water Partition
Constant (KOW)
Naphthalene
Dibenzofuran
Phenanthrene
Pyrene
Decreasing Vapor
Pressure/Water Solubility
Benzo(a)pyrene
Sample Sediment Properties
Log KOC1
Kd2 (L/kg)
Henry’s Const.
(-)
Naphthalene
3.53
464
0.011
Phenanthrene
4.71
7017
0.0029
Anthracene
4.69
6682
0.0027
Pyrene
5.23
23284
0.00092
Benzo(a)
Anthracene
6.04
149599
0.00024
Chrysene
6.07
160997
0.0003
Benzo(a)Pyrene
6.73
734309
0.000093
Chemicals
Organic Carbon
Content
0.13 (mean fraction on dry basis)
– Chemical Equilibrium Partitioning Constant between Organic Carbon &
Water (normalized for organic carbon content)
2K – Chemical Equilibrium Partitioning Constant between Sediment & Water
d
1K
OC
Irreversible Fraction
* Kan et al., Environmental Science and Technology, 32, 892-902,1998.
SEI of various sediment fractions
X-ray Maps for Specimen (1)
Secondary
Calcium
Backscatter
Silicon
Carbon
Oxygen
SEI, EDS for Specimen (2)
BEI
C
S
EDS for specimen (5)
C
Ca
Fe
Ca
C Al
O
Fe
C
Ca
O
Fe
Irreversible Sorption on Organic
Carbon – Proposed Mechanisms
• Based on Form and Distribution of Organic
Carbon in Sediments
–
–
–
–
Slow Diffusion from coal-derived particles
‘Soft’ and ‘Hard’ Carbon – Ageing Effects
Glassy and Rubbery Phases
Condensed (black carbon, soot etc) and Amorphous
Carbon (humic acid based)
– Conformational Changes and Binding
• Some forms offer greater sorption capacity and
slower desorption rates
• Ageing and slow diffusion
Problems of Interest
• Normalization of Desorption Resistant Organic
Carbon Fraction in Sediments
– Field Sediment characterization/bioavailability
• Bioavailability and Mobility of Metals
– Presence of Sulfides and other condensed phases
– Interaction with Organic Phases
– Effect of biological activity/dissolved
oxygen/pH/redox conditions
– Remediation methods for metal contaminated
sediments
Options for Remediation
• Monitored Natural Recovery
– Natural attenuation
– Least Expensive
• In-situ Capping
– Clean material cover over contaminated zone
– Motive is to allow undisturbed natural recovery
• Dredging
– Physical removal of contaminated material
– Relocation for storage/disposal/treatment
In-situ Sediment Capping
NO SEDIMENT CAP
HIGH CHEMICAL FLUX
WATER
SEDIMENT
In-situ Sediment Capping
Non Adsorbing Sand Cap
Lower Flux (Organics)
Diffusional Barrier
WATER
SAND CAP
SEDIMENT
In-situ Sediment Capping
Organics Adsorbing Soil
Cap
Lower/Delayed Flux Breakthrough for organics
WATER
CLEAN SOIL/SEDIMENT
SAND CAP
SEDIMENT
In-situ Sediment Capping
Organics Adsorbing Cap
Mat
Lower/Delayed Flux Breakthrough for Organics
WATER
MAT/TEXTILE WITH CARBON
SAND CAP
SEDIMENT
In-situ Sediment Capping
Reactive Cap Mat
Lower/Delayed Flux Breakthrough
In-situ Degradation of
Organics
WATER
ACTIVE REACTIVE AGENT LAYER
MAT/TEXTILE WITH CARBON
SAND CAP
SEDIMENT
In-situ Sediment Capping
WATER
ACTIVE REACTIVE AGENT
MAT/TEXTILE WITH ADSORBENT
SAND CAP
Contamination
SEDIMENT
LCAP
Image: Sediment Profiling Camera (http://www.vims.edu/bio/benthic/)
Problems of Interest
• Active Capping Layer
– Photocatalytic Degradation of Organic Chemicals
Contaminated Sediments in a Cap Framework
•
•
•
•
•
Mass Transfer Enhancement
Low Oxygen Systems
Optical Fibers
Extension to use of sunlight
Soil Remediation
• Capping of Metals contaminated sediments
• Capping Materials Research
– High Physical Integrity
– Incorporate Sensing/Remediation Networks
• Instrumentation for in-situ monitoring
Options for Remediation
• Monitored Natural Recovery
– Natural attenuation
– Least Expensive
• In-situ Capping
– Clean material cover over contaminated zone
– Motive is to allow undisturbed natural recovery
• Dredging
– Physical removal of contaminated material
– Relocation for storage/disposal/treatment
Dredging, Relocation & Treatment
Image Credit: US Army Corps of Engineers
Chemical Release During Dredging
Chemical Release During Dredging
Evaporation
AIR
Flow Direction
Q- Volumetric rate
Cw solution concentration
Cw,in
WATER
Resuspended
particles
Porewater
concentration
Concentration
on particles
Cpw
CS
Solubilization Pathways and
Flux (N) from bed-to-water
Contaminated
bed source
UNCONTAMINATED
SEDIMENT BED
Cw,out
Environmental Impact
AIR POLLUTION IMPACT
Meteorology and Dispersion
AIR EMISSION RATES
Evaporative Mass Transfer
AQUEOUS CONCENTRATION
Desorption
SUSPENDED SOLIDS
BOUND CHEMICAL
Chemical Contamination of
Bed Sediment
SUSPENDED SOLIDS
CONCENTRATION
Turbidity Generation Per
Volume Dredged
DREDGING
MECHANICS
Mechanical or Hydraulic
Dredging
Experimental Setup
MOTOR
Air
Inlet
Flow
Meter
Eccentric Drive
Shaft
PAH
Trap
To Vacuum Pump
Carbon
Trap
Air
Flow
Air Flow Distributor
Oscillating Grid
Sediment
Suspension
Outlet Drain
EXPERIMENTAL SIMULATION OF SEDIMENT RESUSPENSION AND
CHEMICAL RELEASE DURING DREDGING
Experimental Setup
MOTOR
Air
Inlet
Flow
Meter
Eccentric Drive
Shaft
PAH
Trap
To Vacuum Pump
Carbon
Trap
Air
Flow
Air Flow Distributor
Oscillating Grid
Sediment
Suspension
Outlet Drain
EXPERIMENTAL SIMULATION OF SEDIMENT RESUSPENSION AND
CHEMICAL RELEASE DURING DREDGING
Total Suspended Solids (TSS)
Aqueous Phase Concentration
Aqueous Concentration, ng/mL
10
1
0.1
Naphthalene
Phenanthrene
Pyrene
Benzo(a) Pyrene
0.01
1
10
100
Time, Minutes
1000
10000
Chemical Flux to Air
10
Naphthalene
Phenanthrene
Pyrene
Flux to Air, ng/cm²/hr
1
0.1
0.01
0.001
0.0001
100
1000
Time, minutes
10000
Mass of Chemical on Suspended Solids, µg
Solids in Suspension (Benzo(a)Pyrene)
Estimated Chemical
Release
Mass = WS0 . TSS . V
WS0 – average initial
chemical concentration in
bed sediment (µg/g)
TSS – total suspended
solids concentration (g/L)
Total Organic Carbon and TSS
12
TSS
OC
% in suspension
10
8
6
4
2
0
1
10
100
time, hr
1000
10000
Particle Size Distribution
100
IHC Composite
2 min
30 min
60 min
6 hr
24 hr
% Passing
10
1
0
0.10
1.00
10.00
Particle Diameter, m
100.00
1000.00
Problems of Interest
• Quantification of Chemical Release
caused by a different dredge-heads
• Relationship between particle size and
chemical concentration – Methods to
quantify/evaluate/predict
– For Organics and Metals
• Instrumentation for real-time, in-situ
analysis to capture the dynamics during
dredging
What happens to the Dredged Material?
Post Dredging Relocation - Treatment
Confined Disposal Facility (CDF)
Confined Disposal Facility
Post-Dredging Treatment Options
•
•
•
•
Capping
Bio/Phyto Remediation
Thermal Treatment
Extraction/Separation
– Supercritical Fluid Extraction
– Accelerated Intense Solvent Extraction
• Electrochemical Methods
• Post Treatment Disposal
– Land Reclamation (e.g.Parking lots, Parks)
– Ocean Disposal
Mudflats
Image Source: Shunya.net
Mudflats
Image Source: Shunya.net
Air Pollution Risk Assessment from
Exposed Dredged Materials
• Large Surface Areas Exposed
– Frequent Cycling of Water Content
• Affects transport properties of chemicals dredged material
– Surface Amendments/ Capping
– Oil Grease
• Emission Flux Data
– Laboratory and Field Pilot Scale Experiments
• Enclosed Space Flux Measurement
– Small Scale Flux Chamber
– Wind Tunnel
• Micrometeorological Method
– Verification with Existing Models
Laboratory Scale Experiments
House
Air
Supply P
Flow Meter
Exhaust
Hood
Drierite
Bubblers
Thermohygrometer
Flux Chamber
10
cm
Sediment
15 cm
PAH trap
- XAD®
m
Flux 
t  A
Pilot Scale CDF- Experimental Setup
Vacuum
Pump
Weather Station
Air Inlet
Adsorbent bed
Surface
Datalogger
Flux Chamber
Sediment
Overflow Drum
Sand
Gravel
Leachate Drum
4 ft
Direct Emission Flux Measurement –
Field Scale – Aerodynamic method
Wind Velocity
Profile
Vertical
Diffusion
A
B
Chemical Vapor
Boundary Layer
C
Advection
Air
Soil
Treated or Contaminated Area of length, L
Sampling Location
A Sampling Mast on upwind boundary
B Sampling Mast at midpoint
C Sampling Mast at downwind boundary
Control volume boundary
Direct Emission Flux
Measurement – Field Scale
• Aerodynamic Method:
12 D1( t )   u   C 


flux( x )   2 ( t ) 
m 1   (ln z)   (ln z) 
– Flux(x) = vertical evaporative flux (mass/area/time) of
chemical
– 1 – von Karman constant (= 0.4)
– D1(t) = chemical exchange coefficient
– 1(t) = eddy exchange coefficient
– u = velocity at a height z
– C = chemical concentration at height, z
–  = atmospheric stability related factors
Pilot Field Scale Experiment
- Aerodynamic Method
Problems of Interest
• Drying and Rewetting of
Exposed Dredging Materials
– Modeling of Contaminant Flux
Response to Complete
Moisture Cycling in a CDF
– Mass transfer from shrinkage
cracks
– Effect and mobility of oilgrease in drying dredged
materials
• Non-invasive Analysis
• Visualization
Flow of air
d
• Instrumentation for Flux
Measurement (Air emissions
from exposed surfaces)
z
Contaminated
Dredged Solids
Convective Transport
Diffusive Transport