Download presentation. - University of California, Santa Barbara

Transport of colloids in unsaturated
porous media:
Explaining large scale behavior based on
pore scale mechanisms
Arturo A. Keller, Sanya Sirivithayapakorn
and Maria Auset
Bren School of Environmental Science & Management
University of California, Santa Barbara
1

Colloids in Groundwater
A B C
50 nm
Photo credit:
A. F.P. Williams, U.S. EPA, http://www.epa.gov/nerlcwww/index.html
B. Nannobacteria Research, http://www.msstate.edu/dept/geosciences/4site/nannobacteria.htm
C. H.D.A Lindquist, U.S. EPA, http://www.epa.gov/nerlcwww/index.html
Bren School of Environmental Science & Management
University of California, Santa Barbara
2

Contaminated Supply?
Leaking Sewer line
Or Septic tank
Vadose
Zone
Contaminants
-Viruses
- Bacteria
Saturated
Zone
Bren School of Environmental Science & Management
University of California, Santa Barbara
3

Courtesy of Bruce Robinson, LANL
Bren School of Environmental Science & Management
University of California, Santa Barbara
4

Fate and Transport of
Colloids
Air
Water
Attached
Inactivated
V
Suspended
Inactivated
Solid
Attached
Inactivated
Bren School of Environmental Science & Management
University of California, Santa Barbara
5

Issues
Mobilization of colloids during
flushing
Air-Water Interface
Thin-water films
Mobile/Immobile water
Bren School of Environmental Science & Management
University of California, Santa Barbara
6

Experimental Setup
Inlet
VCR/monitor
Pressurized
reservoir
Inlet valve
to micromodel
Video
Camer
a
Video image
Pump
PEG*
Micromodel
Microscope
*Polyethylene Glycol Solution
Outlet
PC with video
capture board
Bren School of Environmental Science & Management
University of California, Santa Barbara
7

1
2
5
3
4
8
6
7
9
15
16
12
14
10
13
11
1
2
100 µm 100 µm 100 µm 100 µm 100 µm
Bren School of Environmental Science & Management
University of California, Santa Barbara
8

1 µm latex spheres at the air-water interface (AWI), X500

MS-2 at the air-water interface (AWI), X1000

Interaction Energy (J)
1.4E-17
1.2E-17
1.0E-17
8.0E-18
6.0E-18
4.0E-18
2.0E-18
0.0E+00
1 um
2um
3 um
0 5 10 15 20
Distance (nm)
3500
3000
2500
2000
1500
1000
500
0
Interaction Energy (kT)
Colloid-colloid interaction in water
(DLVO theory)
Colloid
Distance
Colloid
2.5E-19
60
Interaction Energy (J)
2.0E-19
1.5E-19
1.0E-19
5.0E-20
MS2
0.05 um
50
40
30
20
10
Interaction Energy (kT)
W = V + A vdw
W = Total interaction energy
V = Electrostatic repulsion
A vdw = van der Waals attraction
0.0E+00
0 5 10 15 20
0
Distance (nm)

MS2
0.05µm
Energy Barrier
(DLVO theory)
3 kT
54 kT
1µm 1000 kT
2µm 2100 kT
3µm 3200 kT
Capillary
10 2 kT
10 3 kT
10 5 kT
10 6 kT
10 6 kT
Water Phase
Energy Barrier
Colloid
Colloid
Air-Water
Interface
Air Phase
Capillary
Capillary

Direction of flow Water Content: 41%
Bren School of Environmental Science & Management
University of California, Santa Barbara
13

First Flush
Water Content: 76%
26 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
14

Water Content: 78%
38 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
15

Water Content:78%
51 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
16

Water Content: 79%
1 min 04 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
17

Water Content: 80%
1min 12 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
18

Water Content: 82%
1min 28 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
19

Water Content: 83%
1min 39 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
20

Water Content: 83%
1min 55 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
21

Water Content: 84%
10 min 09 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
22

Water Content: 68%
2 h 59 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
23

Water Content: 62%
3 h 34 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
24

Water Content: 58%
3 h 49 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
25

Water Content: 55%
4 h 08 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
26

Water Content: 47%
4 h 51 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
27

Water Content: 43%
5 h 04 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
28

Second Flush
11 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
29

13 sec after
second flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
30

Water Content: 77%
23 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
31

Water Content: 79%
1 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
32

Water Content: 80%
1 min 18 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
33

Water Content: 82%
1 min 35 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
34

Water Content: 83%
2 min after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
35

Water Content: 85%
2 min 28 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
36

Water Content: 87%
5 min 49 sec after flush
Bren School of Environmental Science & Management
University of California, Santa Barbara
37

Key Findings
Sorption onto AWI is “irreversible”
Colloids sorbed onto AWI can form clusters
Colloids trapped in thin water films
Colloids sorbed onto AWI can be transported
Along with the moving air bubble
As colloidal clusters
As water is remobilized
Bren School of Environmental Science & Management
University of California, Santa Barbara
38

Pressure
Transducers
Data Acquisition
System
Injection
Port
Flow
Meter
Pump
Water
Reservoir
Unsaturated
Column
Setup
Sample
Collection
Bren School of Environmental Science & Management
University of California, Santa Barbara
39

C/Co, KCl
C/Co, KCl
C/Co, KCl
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
KCl
MS2
0.05 um 3 um
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.0
0.00
0.0 0.5 1.0 1.5 2.0 2.5
0.8
0.18
KCl
MS2
0.7
0.05 um 3 um 0.16
0.6
0.5
0.4
0.3
0.2
0.1
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.0
0.00
0.0 0.5 1.0 1.5 2.0 2.5
0.8
0.18
KCl
MS2
0.7
0.05 um 3 um 0.16
0.6
0.5
0.4
0.3
0.2
0.1
0
0.0 0.5 1.0 1.5 2.0 2.5
Pore volume
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
C/Co, Colloids
C/Co, Colloids
C/Co, Colloids
S w = 44%
S w = 37%
S w = 27%
Breakthrough
curves
for
steady water
contents

θ
0.1 0
0.45
0.40
0.4 5
0.4 0
0.3 5
0.3 0
0.2 5
0.2 0
0.1 5
-4
60
0
Time (min)
Z = 5 cm
Z = 15 cm
Z = 25 cm
Z = 35 cm
Z = 45 cm
Z = 55 cm
MS2
0.05um
3um
Water content, θ, (cm -3 -cm -3 )
Water content, θ, (cm -3 -cm -3 )
0.40
0.35
0.35
0.30
0.25
0.30
0.20
0.25
0.15
0.20
0.10
0.15
0.05
0.10
0.00
0
0.45
10 20 30 40 50 60
0.40
0.40
0.35
0.35
0.30
0.25
0.30
0.20
0.25
0.15
0.20
0.10
0.15
0.05
0.10
0.00
0.45
0 10 20 30 40 50 60
0.40
C/Co
C/Co
S w,i
= 44%
S w,i
= 37%
BT curves
during
flushing
Peak of BT-curves appear
immediately after column is
saturated
0.40
0.35
Water content, θ, (cm -3 -cm -3 )
0.35
0.30
0.25
0.20
0.15
0.30
0.25
0.20
0.15
0.10
0.05
C/Co
S w,i
27%
0.10
0 10 20 30 40 50 60
Time (min)
0.00

Mass recovered (%)
40
30
20
10
MS2
Steady Flushing Total
Steady water content
Colloid recovery
Recovery of
0
0.11 0.15 0.18
MS2>0.05mm>3mm
Mass recovered (%)
40
30
20
10
0.05 µm
Steady Flushing Total
Recovery increases with
water content
Flushing
Much higher recovery
Mass recovered (%)
0
40
30
20
10
0
3 µm
0.11 0.15 0.18
Steady Flushing Total
0.11 0.15 0.18
Peak of BT-curves appear
immediately after column is
saturated
Recovery decreases
significantly with increase
initial water content
Initial water content (cm -3 -cm -3 )

Connection to larger scale
Under unsaturated conditions, steady-state state water
content, slow flow
Colloid breakthrough is low due to sorption at AWI
Sorption to solid interface can be significant due to low
flowrates
Colloids trapped in immobile water
Flushing releases colloids:
Sorbed
Remobilized with water
In clusters
Bren School of Environmental Science & Management
University of California, Santa Barbara
43

Conclusions
Significant storage of colloids under
unsaturated conditions
Modelling of vadose zone transport is
important to understand the risk of
mobilization
Understanding pore-scale mechanisms can
help guide larger-scale experiments
produce better models
Bren School of Environmental Science & Management
University of California, Santa Barbara
44

Acknowledgements
Funding from UCSB Academic Senate
Committee on Research
Bren School of Environmental Science & Management
University of California, Santa Barbara
45