Agricultural & Biological Engineering Outline - UF/IFASsoils.ifas.ufl.edu/lqma/SEED/SWS6262/Lecture notes/Gao-10.pdf · 3 University Florida Agricultural & Biological Engineering

1

UniversityUniversity FloridaFloridaAgricultural & Biological Engineering

Transport of Colloidal Particles in

the Vadose Zone


Outline

• Introduction

• Transport Mechanisms

l l• Pore-Scale Visualization

• Experimentation and Modeling


Colloids

• Natural Colloids

Abiotic:

All kinds of minerals, “Particulate” organic All kinds of minerals, Particulate organic matter …

Biotic:

Viruses, Bacteria, & Protozoa (“Biocolloid”)

• Engineered Nanoparticles

e.g. Buckyball (C60), Nanotubes, Oxides


Size Range

source: CERN http://microcosm.web.cern.ch/microcosm

10cm1cm1mm

1cm

100μm10μm


Colloids in Subsurface

• Facilitate contaminant transport

• Affect soil-profile Affect soil profile development

• Microbial pathogens

• Remediation

Source: McCarthy and Zachara , ES&T 1989


2


www.hanford.gov


• Introduction


l l

Outline

• Pore-Scale Visualization



Transport Processes

• Advection: transport due to bulk motion of the porewater.

• Dispersion: spreading arising from velocity

Vadose Zone

water & airin pores

arising from velocity variations.

• Deposition: processes that immobilize porewater colloids.

• Mobilization: processes that release colloids into porewater.

Zone

SaturatedZone

water fillspores

Water table


Deposition Mechanisms

Vadose water & air

in pores

GrainAttachment

waterflow

bil

airwaterflow

bil

air

grai

n su

rfac

e

waterflow

(aroundbubble)

waterflow

(aroundbubble)

Water InterfaceAirAttachment

-e Pore-StrainingAttachment

waterflow

waterflow

Film-StrainingAttachment

immobilecolloidimmobilecolloidgr

ain

surf

ace

Zone

SaturatedZone

p

water fillspores

Water table

mobilecolloid

immobilecolloid

tot

mobilecolloid

immobilecolloid

tot

airbubble

mobilecolloid

immobilecolloid

airbubble

mobilecolloid

immobilecolloid

grai

n su

rfac

emobilecolloid

immobilecolloid

mobilecolloid

immobilecolloid

grai

n su

rfac

e

waterflow

wfilm

dp

mobilecolloid

airwaterflow

wfilm

dp

mobilecolloid

air


Deposition Mechanisms

Film-StrainingAttachment

GrainAttachment

Air-Water InterfaceAttachment

Pore-StrainingAttachment

immobilecolloid

waterflow

air waterflow

(aroundbubble)

waterflow

immobilecolloid

waterflow

air waterflow

(aroundbubble)

waterflow

grai

n su

rfac

e

grai

n su

rfac

e

waterflow

wfilm

dp

mobilecolloid

mobilecolloid

immobilecolloid

tot

air

mobilecolloid

airbubble

mobilecolloid

immobilecolloid

immobilecolloid water

flow

wfilm

dp

mobilecolloid

mobilecolloid

immobilecolloid

tot

air

mobilecolloid

airbubble

mobilecolloid

immobilecolloid

immobilecolloid

grai

n su

rfac

e

grai

n su

rfac

e


Mobilization Mechanisms

Vadose water & air

in pores

Film-ExpansionReleasewaterflow

waterflow

Air-Water InterfaceScouring

waterflow

waterflow

n su

rfac

e

ColloidDispersion

waterflow

tot

waterflow

totgrai

n su

rfac

e

ShearMobilization

waterflow

waterflow

Zone

SaturatedZone

in pores

water fillspores

Water tablewfilm

dp

mobilecolloid

immobilecolloid

wfilm

dp

mobilecolloid

immobilecolloid

grai

n su

rfac

e

mobilecolloidmobilecolloid

grai

n

mobilecolloid

detachedcolloid

mobilecolloid

detachedcolloid

mobilecolloidmobilecolloidgr

ain

surf

ace

3


Mobilization Mechanisms

ShearMobilization

Air-Water InterfaceScouring

Film-ExpansionRelease

ColloidDispersion

waterflow

waterflow

waterflow

waterflow

tot

waterflow

waterflow

waterflow

waterflow

totgrai

n su

rfac

e

urfa

ce

mobilecolloid

mobilecolloid

wfilm

dp

mobilecolloid

immobilecolloid

mobilecolloid

detachedcolloid

mobilecolloid

mobilecolloid

wfilm

dp

mobilecolloid

immobilecolloid

mobilecolloid

detachedcolloid

grai

n su

rfac

e

grai

n su

rfac

e

grai

n s


Immobile Water (storage zones for nanopoarticles?)

Other Mechanisms?

Air


Water displaces air, which converts Immobile-water zonesto mobile-water zones and releases stored colloids

Other Mechanisms?

Air


• Introduction


l l

Outline

• Pore-Scale Visualization



Pore-Scale VisualizationsFluorescent & Bright Field Microscopy


Three Deposition Mechanisms

Pore-Scale Visualizations

Three Deposition Mechanisms

4


Particle Deposition (1)Captured by Air Bubble

100 μm


Particle Deposition (2)Strained in Thin Water Film


Particle Deposition (3)Trapped in Immobile Water

Air

100 μm100 μm

Water

Immobile water


Two Mobilization Mechanisms

Pore-Scale Visualizations

Two Mobilization Mechanisms


Immobile Water

Particle Mobilization (1)Expansion of Thin Water Film

Air

Water

100 μm

Gao et al. 2006. Water Resources Research, 42(1), W01410


Immobile Water

Particle Mobilization (2)Conversion of Immobile Water

Air

Water

100 μm

Gao et al. 2006. Water Resources Research, 42(1), W01410

5


Pore-Scale VisualizationsConfocal Laser Scanning Microscopy


Image Analyses

Confocal Laser Scanning Image

COUNTING PARTICLES


w

ws KM

KNMM

11000

1500

2000

s

Image Analyses

wss C

X

Mk

dt

dC 2)1(

Kinetics!

0

500

1000

0 2000 4000 6000 8000 10000

Mw

Ms


Outline

• Introduction

• Pore-Scale Visualization: Movies

l d• Column Experimentation and Modeling: Homogeneous & Heterogeneous


Homogeneous ColumnsColumn Break Through Curves


Flow Equations

• Darcy’s Law

• Laplace Equation (Steady Flow)

• Diffusion Equation (Transient Flow)• Diffusion Equation (Transient Flow)

• Richards Equation

• Brooks and Corey Equation

• Mualem–van Genuchten Equation

6


Model Summary

• Column moisture content: One-dimensional form of the flow equation

E ample )]1([

kExample:

• Column chemistry: solute transport model

Example:

)]1([

z

kzt

z

Cv

z

CD

zt

C HHH

)(


• Particle transport: One-dimensional convection-dispersion equation

Example:

Model Summary

• Different kinetics expressions

z

qC

z

CD

zt

C

t

C

t

C knk

)(][

))1((...

))1(()( 1

First-order rate law

Second-order rate law


Effects of Flow Perturbations on Clay Release

60

80

100

/L)

0.15

0.2Kaolinite

Steady Flow: Q0=10 mL/min

Transient Flow: Q1= 20 mL/min Q2=40 mL/min Q3=70 mL/min

0

20

40

60

0 2000 4000 6000 8000Cumulative Volume (mL)

C (

mg/

0

0.05

0.1


80

100

6

7

8

pH

Effects of pH Perturbations on Clay Release

0

20

40

60

2800 3800 4800 5800 6800

Cumulative Volume (mL)

C (

mg

/L)

0

1

2

3

4

5

pH

Kaolinite


Heterogeneous Columns

• Coarse sand was packed in the center of the column surrounded by fine sandby fine sand

• Clay applied to column under conditions of steady flow and chemical conditions


Simulations of Flow and Moisture

Θ

7


Visualizations

100 μm


Clay Transport through Saturated Heterogeneous Column


Clay Transport through Unsaturated Heterogeneous Column


Laboratory ColumnsIn-Suit Measurement

Cornell High Energy Synchrotron Source


Particle Facilitated Transport

Clay-Metal Transport

0.8

1

1.2

nte

nt

-0.2

0

0.2

0.4

0.6

0 500 1000 1500 2000

t (sec)

wat

er a

nd

Cd

co

n

w ater

Cd-Clay Complex

Model


www.hanford.gov

Documents

Agricultural & Biological Engineering Outline - UF/IFASsoils.ifas.ufl.edu/lqma/SEED/SWS6262/Lecture notes/Gao-10.pdf · 3 University Florida Agricultural & Biological Engineering