ADVANCES IN UNDERSTANDING SORPTION AND TRANSPORT PROCESSES AFFECTING THE FATE OF ENVIRONMENTAL...
1
ADVANCES IN UNDERSTANDING SORPTION AND TRANSPORT PROCESSES AFFECTING THE FATE OF ENVIRONMENTAL POLLUTANTS IN THE SUBSURFACE Hrissi K. Karapanagioti 1 , David Werner 2 , Charles J. Werth 3 1 Department of Chemistry, University of Patras, 26500 Patras, Greece, [email protected] 2 School of Civil Engineering and Geosciences, Newcastle University, UK, [email protected] 3 Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, USA, [email protected] The attachment of environmental pollutants to solid matrices in soils and sediments is a well-investigated physicochemical process of fundamental importance for predicting pollutant fate, and the risk that pollutants pose to human and ecological receptors. The continuing refinement of our mechanistic process understanding challenges us to improve the representation of sorption in computational pollutant fate models in order to provide more realistic predictions of pollutant fate in complex soil and aquifer systems, and cleanup times for alternative soil and groundwater remediation technologies . We have edited this special issue entitled “Sorption and Transport Processes Affecting the Fate of Environmental Pollutants in the Subsurface” with the following objectives: a) to present studies of processes that are normally not included or are simplified in large-scale computational models because of the constraints on computation time or scale differences between experimental settings and field work, b) to discuss thoroughly the importance of the new findings related to sorption processes in terms of their wider environmental significance, and c) to strengthen the ties between sorption and transport processes through advances in experimental and field work as well as modelling studies. We feel that it is valuable to collect in one issue papers that would otherwise appear in a range of issues / journals, and we hope that this special issue will prove valuable for those at all stages of inquiry into this topic. Nine papers were accepted. They are separated into four main topics as follows: a) new experimental methodologies and parameter evaluation, b) implications for pollution remediation and reclamation methods, c) challenges in modifying and selecting existing models to interpret experimental results, and d) subsurface properties that affect sorption and transport. Pollutants studied include: biocolloids, metals (arsenic, chromium, nickel), organic compounds such as hydrocarbons, chlorinated hydrocarbons, micropollutants (PAHs, PCBs), and pesticides (glyphosate, 2,4-D). Overall, our special issue indicates that existing models need modification to fit experimental data, and there remain gaps in our understanding of the underlying mechanisms controlling sorption and transport. There is still much work to be done in this fascinating area! Acknowledgements The authors would like to thank David A. Sabatini for helpful discussions and guidance. This presentation is funded by the University of Patras and by the University of Patras Research Committee Program “Karatheodori 2009” Jeppu et al. uses a modified batch reactor system to study equilibrium-reactive transport problems of metals. This paper provides a novel experimental system for investigating one-dimensional transport problems involving equilibrium geochemical reactions. The proposed system uses a set of sequentially coupled batch reactors that directly mimic a typical one-dimensional numerical grid. Com parison ofthe proposed batch reactorexperim ents w ith num erical grids Jeppu and Clement propose a new isotherm model that combines modified traditionally used isotherms and can be used to simulate pH-dependent metal adsorption. This analytical isotherm model, is identified as the modified Langmuir-Freundlich (MLF) isotherm. The isotherm was tested using adsorption data collected for arsenic and goethite-coated-sand systems. Com parison ofJeppu and Clem ent’s(2012)m odified Langm uir- Freundlich isotherm m odel predictionsw ith isotherm data 2 0.00 0.02 0.04 0.06 0.08 0.10 0.00 1.00 2.00 3.00 4.00 5.00 As(V) adsorbed (m g/g sand) As(V) concentration (m g/L) pH 4 pH 5.5 pH 7 pH 8.5 pH 10 Syngouna and Chrysikopoulos use column studies along with theoretical approximations to evaluate the combined effects of grain size and pore water velocity on the transport of three biocolloids in water saturated porous media. The main objective of this study is to evaluate the combined effects of grain size and pore water velocity on the transport in water saturated porous media of three waterborne fecal indicator organisms (Escherichia coli, MS2, and X174) in laboratory-scale columns packed with clean quartz sand. AC amendment is an innovative in-situ method for the remediation of sediments polluted by hydrophobic organic compounds, but the performance depends on the microscale spatial distribution of the AC in the polluted sediment. Modelling and 5 year field monitoring data confirm the long-term benefits of AC amendment and illustrate the importance of achieving a good sorbent distribution during the initial AC placement. Cho et al. evaluate a sorbent- based sediment remediation method considering site- specific conditions such as small scale heterogeneity by bringing together monitoring results and modelling. Incorporating the m icroscale in pollutantfate m odels Slide 1 2. Interparticle m asstransfer AC diam eter150 m Grid-spacing 200 m M icro-scale m odel: M ixing conditionsin the field are differentfrom the laboratory. Thisshould resultadditional m ass transferresistance. Ranieri and Young through a field study point to the importance of clogging and also sorption as mechanisms affecting the effectiveness of sub-surface flow constructed wetlands. Chromium (Cr) and Nickel (Ni) removal was also assessed as a function of increased clogging that occurred in the cws over a four year research program. Proportionality between increasing clogging and sediment accumulation of metals was observed, especially for Ni. Adsorption to the original matrix and the accumulated sediment is a removal mechanism consistent with available data. Linear free energy relationships (LFERs) were established which estimate stable carbon and hydrogen isotope enrichment factors for equilibrium sorption to geosorbents from equilibrium vapor-liquid isotope effects. For benzene in the figure above it is illustrated that the 13C and 2H-benzenes will sorb more weakly because their vapor pressures are higher. The LFERs are useful since very few experimental data for fractionation by sorption are available. 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 2 3 4 5 6 7 VaporPressure log P (Pa) log Koc(Lkg -1 OC ) Benzene Benzene- 12 12 C- 1 H Benzene Benzene- 13 13 C M onoaromatics Chloroethenes n-Alkanes Cycloalkanes Branched alkanes Regression (n-Alkanes) Regression (M onoarom atics) Regression (Chloroethenes) Regression (Branched alkanes) Regression (Cycloalkanes) Benzene Benzene- 2 H Höhener and Yu demonstrate the ability of linear free energy relationships (LFERs) to predict slight shifts in the isotopic ratio of groundwater pollutants which are due to sorption. Magga et al. test possible modifications that improve the reliability of kinetic models and their parameter values during the evaluation of pesticide sorption experiments. S orption isotherm (Freudlich) B atch Sorption tests Breakthrough curves C ontinuous flow tests on soilcolum ns N on-equilibrium 2-site sorption m odel 2-region and 2-site sorption m odel 0 5 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 (b ) Soilcolum n data fo r 2,4 -D F itting breakthroug h curve C * =C /C 0 τ= tu 0 /L Param eter Glyphosate 2,4-D m a (s -1 ) 10 7 10 3 2 10 73 3 x . x . 8 9 10 04 1 10 45 3 x . x . im a (s -1 ) 11 8 10 43 4 10 22 3 x . x . 10 10 0 2 x . m f 3 10 15 1 714 0 x . . 0 0. im f 4 10 11 1 155 0 x . . 3 10 84 5 0247 0 x . . c k (m 2 s -1 ) 10 7 10 3 1 10 51 4 x . x . 6 6 10 8 9 10 9 7 x . x . m φ 3 0. 110 0 362 0 . . 0 10 20 30 40 50 60 0.0 0.2 0.4 0.6 0.8 1.0 Soilcolu m n d a ta for g lyp ho sa te Fittin g b rea kthro ug h cu rve C * =C /C 0 τ= tu 0 /L (a) Glyphosate 2,4-D A thorough review paper by Cheng et al. presents the impact of mineral micropores on the transport and fate of organic contaminants especially when the porous geological media have very low organic carbon contents. Organic contaminants can adsorb into the hydrophobic micropore spaces present in porous geological media through displacement of the sorbed water, and their desorption rate is very slow due to hindered molecular diffusion Because of the inhibitory effect on abiotic and biotic transformations, micropore sorption can cause preservation of anthropogenic organic contaminants in the subsurface and may increase their persistence to the time scale of geological ages under appropriate conditions. Werner et al., discuss the effect of grain-scale sorption rate limitations on the groundwater pollutant fate based on experimental results and the Damköhler number. Naphthalene and Sand 0 0,000005 0,00001 0,000015 0,00002 0,000025 0 2000 4000 6000 Tim e [m in] C aq outlet[g/cm 3] Data D iffkin + stdev -stdev C hloro-benzene and Sand 0 0,2 0,4 0,6 0,8 1 1,2 0 500 1000 1500 2000 2500 3000 tim e [m in] C aq /C inll Phenanthrene and Sand 0,E +00 2,E -07 4,E -07 6,E -07 8,E -07 1,E -06 0 5 10 15 20 25 30 Tim e [years] C aq @ 500 m dow nstream [g/cm3] D iffkin First-orderkin E quilibrium Phenanthrene and Sand w ith P orous P articles 0,E +00 2,E -07 4,E -07 6,E -07 8,E -07 1,E -06 0 2 4 6 8 10 12 Tim e [years] C aq @ 500 m dow nstream [g/cm3] D iffkin First-orderkin E quilibrium Relatively high groundwater velocities in combination with a low sorption coefficient Kd and slow diffusion limited sorption kinetic rates are necessary conditions to justify the implementation of grain- scale sorption rate limitations in groundwater contaminant fate models.
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Transcript of ADVANCES IN UNDERSTANDING SORPTION AND TRANSPORT PROCESSES AFFECTING THE FATE OF ENVIRONMENTAL...
ADVANCES IN UNDERSTANDING SORPTION AND TRANSPORT PROCESSES AFFECTING THE FATE OF ENVIRONMENTAL POLLUTANTS IN THE SUBSURFACE
Hrissi K. Karapanagioti1, David Werner2, Charles J. Werth3
1Department of Chemistry, University of Patras, 26500 Patras, Greece, [email protected] of Civil Engineering and Geosciences, Newcastle University, UK, [email protected]
3Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, USA, [email protected]
The attachment of environmental pollutants to solid matrices in soils and sediments is a well-investigated physicochemical process of fundamental importance for predicting pollutant fate, and the risk that pollutants pose to human and ecological receptors. The continuing refinement of our mechanistic process understanding challenges us to improve the representation of sorption in computational pollutant fate models in order to provide more realistic predictions of pollutant fate in complex soil and aquifer systems, and cleanup times for alternative soil and groundwater remediation technologies . We have edited this special issue entitled “Sorption and Transport Processes Affecting the Fate of Environmental Pollutants in the Subsurface” with the following objectives: a) to present studies of processes that are normally not included or are simplified in large-scale computational models because of the constraints on computation time or scale differences between experimental settings and field work, b) to discuss thoroughly the importance of the new findings related to sorption processes in terms of their wider environmental significance, and c) to strengthen the ties between sorption and transport processes through advances in experimental and field work as well as modelling studies. We feel that it is valuable to collect in one issue papers that would otherwise appear in a range of issues / journals, and we hope that this special issue will prove valuable for those at all stages of inquiry into this topic.Nine papers were accepted. They are separated into four main topics as follows: a) new experimental methodologies and parameter evaluation, b) implications for pollution remediation and reclamation methods, c) challenges in modifying and selecting existing models to interpret experimental results, and d) subsurface properties that affect sorption and transport. Pollutants studied include: biocolloids, metals (arsenic, chromium, nickel), organic compounds such as hydrocarbons, chlorinated hydrocarbons, micropollutants (PAHs, PCBs), and pesticides (glyphosate, 2,4-D). Overall, our special issue indicates that existing models need modification to fit experimental data, and there remain gaps in our understanding of the underlying mechanisms controlling sorption and transport. There is still much work to be done in this fascinating area!
AcknowledgementsThe authors would like to thank David A. Sabatini for helpful discussions and guidance. This presentation is funded by the University of Patras and by the University of Patras Research Committee Program “Karatheodori 2009”
Jeppu et al. uses a modified batch reactor system to study equilibrium-
reactive transport problems of metals.
This paper provides a novel experimental system for investigating one-dimensional transport problems involving equilibrium geochemical
reactions. The proposed system uses a set of sequentially coupled batch reactors that directly mimic a typical
one-dimensional numerical grid.
Comparison of the proposed batch reactor experiments with numerical grids
Jeppu and Clement propose a new isotherm model that combines modified traditionally used isotherms and can be used to simulate pH-dependent metal
adsorption.
This analytical isotherm model, is identified as the modified Langmuir-
Freundlich (MLF) isotherm. The isotherm was tested using adsorption
data collected for arsenic and goethite-coated-sand systems.
Comparison of Jeppu and Clement’s (2012) modified Langmuir-Freundlich isotherm model predictions with isotherm data 2
0.00
0.02
0.04
0.06
0.08
0.10
0.00 1.00 2.00 3.00 4.00 5.00
As(
V) a
dsor
bed
(mg/
g s
and)
As(V) concentration (mg/ L)
pH 4
pH 5.5
pH 7
pH 8.5
pH 10
Syngouna and Chrysikopoulos use column studies along with theoretical
approximations to evaluate the combined effects of grain size and pore water velocity
on the transport of three biocolloids in water saturated porous media.
The main objective of this study is to evaluate the combined effects of grain
size and pore water velocity on the transport in water saturated porous
media of three waterborne fecal indicator organisms (Escherichia coli, MS2, and X174) in laboratory-scale columns
packed with clean quartz sand.
AC amendment is an innovative in-situ method for the remediation of sediments polluted by hydrophobic organic compounds, but the
performance depends on the microscale spatial distribution of the AC in the polluted sediment.
Modelling and 5 year field monitoring data confirm the long-term benefits of AC amendment and illustrate the importance of achieving a good
sorbent distribution during the initial AC placement.
Cho et al. evaluate a sorbent-based sediment remediation method considering
site-specific conditions such as small scale heterogeneity by bringing together
monitoring results and modelling. Incorporating the microscale in pollutant fate models Slide 1
2. Interparticle mass transfer
AC diameter 150 m
Grid-spacing 200 m
Micro-scale model:
Mixing conditions in the field are different from the laboratory. This should result additional mass transfer resistance.
Ranieri and Young through a field study point to the importance of clogging and also sorption as mechanisms affecting the effectiveness of sub-surface flow
constructed wetlands.
Chromium (Cr) and Nickel (Ni) removal was also assessed as a function of increased clogging that
occurred in the cws over a four year research program. Proportionality between increasing
clogging and sediment accumulation of metals was observed, especially for Ni. Adsorption to the
original matrix and the accumulated sediment is a removal mechanism consistent with available data.
Linear free energy relationships (LFERs) were established which estimate stable carbon and
hydrogen isotope enrichment factors for equilibrium sorption to geosorbents from
equilibrium vapor-liquid isotope effects. For benzene in the figure above it is illustrated that
the 13C and 2H-benzenes will sorb more weakly because their vapor pressures are higher. The LFERs are useful since very few experimental data for fractionation by sorption are available.
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
2 3 4 5 6 7
Vapor Pressure log P (Pa)
log
Koc
(L k
g-1O
C)
BenzeneBenzene--1212CC--11HH
BenzeneBenzene--1313CC
MonoaromaticsChloroethenes
n-Alkanes
CycloalkanesBranched alkanes
Regression (n-Alkanes)
Regression (Monoaromatics)
Regression (Chloroethenes)
Regression (Branched alkanes)
Regression (Cycloalkanes)
BenzeneBenzene--22HH
Höhener and Yu demonstrate the ability of linear free energy relationships
(LFERs) to predict slight shifts in the isotopic ratio of groundwater pollutants
which are due to sorption.
Magga et al. test possible modifications that improve the reliability of kinetic
models and their parameter values during the evaluation of pesticide sorption
experiments.
Sorption isotherm (Freudlich)
Batch Sorption tests
Breakthrough curves
Continuous flow tests on soil columns
Non-equilibrium 2-site sorption model
2-region and 2-site sorption model
0 5 10 15 200.0
0.2
0.4
0.6
0.8
1.0 (b)
Soil column data for 2,4-D Fitting breakthrough curve
C* =
C/C
0
τ=tu0/L
Parameter Glyphosate 2,4-D
ma (s-1) 107 103210733 x.x. 89 1004110453 x.x.
ima (s-1) 118 1043410223 x.x. 101002 x.
mf 3101517140 x.. 00.
imf 4101111550 x.. 31084502470 x..
ck (m2 s-1) 107 103110514 x.x. 66 10891097 x.x.
mφ 30. 11003620 ..
0 10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0
Soil column data for glyphosate Fitting breakthrough curve
C* =C
/C0
τ=tu0/L
(a)
Glyphosate
2,4-D
A thorough review paper by Cheng et al. presents the impact of mineral
micropores on the transport and fate of organic contaminants especially when the porous geological media have very
low organic carbon contents.
Organic contaminants can adsorb into the hydrophobic micropore spaces present in porous
geological media through displacement of the sorbed water, and their desorption rate is very
slow due to hindered molecular diffusionBecause of the inhibitory effect on abiotic and biotic transformations, micropore sorption can cause preservation of anthropogenic organic
contaminants in the subsurface and may increase their persistence to the time scale of geological
ages under appropriate conditions.
Werner et al., discuss the effect of grain-scale sorption rate limitations on the groundwater pollutant fate based on
experimental results and the Damköhler number.
Naphthalene and Sand
0
0,000005
0,00001
0,000015
0,00002
0,000025
0 2000 4000 6000
Time [min]
Ca
q o
utle
t [g
/cm
3]
Data
Diff kin
+ stdev
- stdev
Chloro-benzene and Sand
0
0,2
0,4
0,6
0,8
1
1,2
0 500 1000 1500 2000 2500 3000
time [min]
Ca
q /C
inll
Phenanthrene and Sand
0,E+00
2,E-07
4,E-07
6,E-07
8,E-07
1,E-06
0 5 10 15 20 25 30
Time [years]
Ca
q @
50
0 m
do
wn
stre
am
[g/c
m3
]
Diff kin
First-order kin
Equilibrium
Phenanthrene and Sand with Porous Particles
0,E+00
2,E-07
4,E-07
6,E-07
8,E-07
1,E-06
0 2 4 6 8 10 12
Time [years]
Ca
q @
50
0 m
do
wn
stre
am
[g/c
m3
]
Diff kinFirst-order kin
Equilibrium
Relatively high groundwater velocities in combination with a low sorption coefficient
Kd and slow diffusion limited sorption kinetic rates are necessary conditions to justify the implementation of grain-scale sorption rate limitations in groundwater
contaminant fate models.
