Sand Saturated and Unsaturated Gravel Porous Media: Pore-scale

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Bren School of Environmental Science & ManagementUniversity of California, Santa Barbara

Transport of Colloids in Saturated and Unsaturated

Porous Media: Pore-scale Observation of Processes

Arturo A. Keller, Sanya Sirivithayapakorn,& Maria Auset


Size Range of Various ParticlesSize Range of Various Particles

0.00001

0.0001

0.0010.01

0.1 1 10 1001000

Size Range (µm)

Colloids

Molecules

Macromolecules

Viruses

Bacteria

Protozoa

Gravel

Sand

Silt

Clay

Effective Pore Diameter

Contaminants


Courtesy of Bruce Robinson, LANL


Saturated Saturated ZoneZone

Vadose Vadose ZoneZone

Leaking Sewer lineLeaking Sewer lineOr Septic tankOr Septic tank

Contaminated Water Supply ?

Contaminants Contaminants --VirusesViruses-- BacteriaBacteria


Colloids in Groundwater

Photo credit: A. F.P. Williams, U.S. EPA, http://www.epa.gov/nerlcwww/index.htmlB. Nannobacteria Research, http://www.msstate.edu/dept/geosciences/4site/nannobacteria.htmC. H.D.A Lindquist, U.S. EPA, http://www.epa.gov/nerlcwww/index.html

50 nm

A B C


Viruses: bioViruses: bio--nanonano--colloidscolloids

Two general shapes:icosahedral (twenty-sided)helical

(a) (b)

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Virus morphologyVirus morphology

Composition

Genome, either DNA or

RNA

Capsid protein: protect viral genome

attach to specific

receptor on host cell


Waterborne Human VirusesWaterborne Human Viruses

Family Genera Note Picornaviridae Enterovirus Represent the largest fraction

of viruses detected in waterCause Hepatitis A, digestive

problems, juvenile diabetes, and poliomyelitis

Reoviridae Reovirus Cause serious inflammation of Rotavirus mucous membrane of stomach

and intestines in childrenCoronaviridae Coronavirus Cause serious bleeding

in the intestines in children Caliciviridae Calcivirus Cause some intestinal problem

Astrovirus in children Adenoviridae Mastadenovirus Cause diarrhea, respiratory&eye infection

hepatitis non-A, non-B


Virus Contaminated SewageVirus Contaminated SewageRaw sewage

Primary

Secondary

Tertiary

WA

STE

W

ATE

R

SLU

DG

E

Ozone at0.3 ppmfor 2 min

Hypochlorousacid at 1 ppm

for 30 min

Incineration

Pasteurization at70oC in alkalinecondition, 60 min

Air-dryingweeks-months

Anaerobicdigestion50oC, 4 weeks

Composting well aerated

< 1%viruses

< 1%viruses

< 1%viruses

Nil virus

Nil virus

1%viruses

1%viruses

10%viruses

0-25%viruses

90%viruses

99%viruses

75-100%viruses

1%viruses


Viruses in the EnvironmentViruses in the Environment

In rivers and oceanviruses can stay viable up to weeksrenewal rate is very high.

In sludge prior to land applicationviable up to 4 months

After application of sludge to soilviable up to 2-5 weeks

Viruses migrated from land application of sludge viable in groundwater up to 2 monthsviable in groundwater for at least 6 months at 10oC


Colloid TransportColloid Transport

Environmental factors that affect colloid

transport

groundwater velocity

quantity, type and size of colloid

geometry of aquifer pores

media surface

ionic strength


Fate and Transport of Viruses

SolidSolid

WaterWater

SuspendedSuspended

Attached Attached

Inactivated Inactivated


SuspendedSuspendedV

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Early Breakthrough in Saturated Porous Media

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40

Pore Volume

C/C

0

KClMS2

Commonly observed in column and field scale experiments

Hypotheses from field and core scale:

Hydrodynamic Chromatography (HDC)Size exclusion


Hydrodynamic Chromatography

rr

r

Small, H., J. Colloid Interface Sci.48:1, 147 (1974)


Experimental Setup

Inlet

Pressurizedreservoir

Microscope

Inlet valveto micromodel

Micromodel

VideoCamera

Video image

VCR/monitor

PC with videocapture boardOutlet

PEG*Pump

*Polyethylene Glycol Solution


100 µm 100 µm 100 µm 100 µm 100 µm

11

2

13

10

14

12

16

15

9

4

5

7

3

6

8

1

1 2


97%

3%

97%3%

7%93%

1) 14%

6) 58%

7) 28%

3) 36%

2) 22%

4) 14%

5) 14%

3 µm colloids 2 µm colloids

1 µm colloids 0.05 µm colloids


0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.70 0.80 0.90 1.00 1.10 1.20 1.30

C/C0

KClModel fir for KCl0.05umModel fit for 0.05um

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.70 0.80 0.90 1.00 1.10 1.20 1.30

C/C0

KClModel fit for KCl3umModel fit for 3um

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.70 0.80 0.90 1.00 1.10 1.20 1.30

C/C0

KClMOdel fit for KClMS2Model fit for MS2

Pore Volume

Breakthrough curves for average water velocity = 1.4 m/d

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Connection to the larger scaleExplains findings at larger scale:

Earlier breakthrough for larger colloids

Early breakthrough increases with fluid velocity

Less dispersion of

Colloids relative to conservative tracer

Larger colloids relative to smaller colloids


Fate and Transport of Colloids

SolidSolid

WaterWater

SuspendedSuspended

AirAir

Attached Attached

Attached Attached Inactivated Inactivated



SuspendedSuspended

Attached Attached

V


Water Content: 41%Direction of flow

Air

Water

Solid


First Flush 12 sec after flush


Water Content: 76%26 sec after flush


Water Content: 78%38 sec after flush

5


Water Content:78%51 sec after flush


Water Content: 79%1 min 04 sec after flush


Water Content: 80%1min 12 sec after flush







6


Water Content: 84%10 min 09 sec after flush


Water Content: 68%2 h 59 min after flush









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Effect of clusters


Key Findings at Pore ScaleSorption onto AWI is “irreversible”

Colloids sorbed onto AWI can form clusters

Colloids sorbed onto AWI can be transported Along with the moving air bubble

As colloidal clusters

As water is remobilized

Colloids may also be at SWA interfacePromotes attachment to SWI


Unsaturated ColumnSetup

Sample Collection

Conductivity Sensor

Pressure Transducers PumpFlow Meter

Injection Port

DI Water

Data AcquisitionSystem


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0 0.5 1.0 1.5 2.0 2.5

C/Co

, KCl

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

C/Co

, Col

loid

s

KCl MS20.05 um 3 um

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0 0.5 1.0 1.5 2.0 2.5

C/Co

, KCl

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

C/Co

, Col

loid

s

KCl MS20.05 um 3 um

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0 0.5 1.0 1.5 2.0 2.5Pore volume

C/C

o, K

Cl

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

C/C

o, C

ollo

ids

KCl MS20.05 um 3 um

Breakthrough curves

forsteady water

contents

Sw = 44%

Sw = 37%

Sw = 27%


Connection to larger scale

Under unsaturated conditions, steady-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


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Key Findings

Microbial retention rate is high: 99.972 % Retention is due sorption onto Air-Water Interface and irreversible attachment onto Soil-Water Interface.


Conclusions

Significant storage of colloids under saturated and unsaturated conditionsModelling of colloid transport is important to understand the risk of mobilizationUnderstanding pore-scale mechanisms can

help guide larger-scale experimentsproduce better models

Sand Saturated and Unsaturated Gravel Porous Media: Pore-scale

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