Fantastic properties of Microbubbles

Fantastic properties
of Microbubbles
AIST Dr.Masayoshi Takahashi
1

Contents of the presentation
・ Fundamental properties of microbubble
・ Gas hydrate formation
・ Water remediation
・ Waste water treatment
2

Goes up
rapidly
Burst at the surface
Ordinary bubble
(Macrobubble)
---- What is microbubble ? ----
Disappear
(Completely dissolved)
Shrinking
Microbubble
< 50μm
Microbubble
(0.05mm) 7

Dissolved gas type
High
pressure
Release
How to make microbubbles (Examples)
Gas
Microbubble
Hydrodynamic Type
Water & Gas
Nozzle
Circulating flow
Microbubble
8

Hydrodynamic type ( High density type )
distilled water
9

Dissolved gas type
A B
C D

Number(/mL)
Bubble-size distribution ( High density type )
1400
1200
1000
800
600
400
200
0
10 20 30 40 50 60
Diameter(μm)
-- Distilled water -- 10
( by a liquid particle counter )

In Distilled water
Rising speed (μm/s)
1000
100
23℃
Rising speed of microbubbles
10 100
Bubble diameter (μm)
measured
Stokes’ law
Microbubble (10μm) ---- about 4 mm/min
11

Bubble diameter (μm)
45
40
35
30
25
20
15
10
5
Collapsing process of microbubble
Disappear
0
0 20 40 60
Time (sec)
80 100 120
Shrinking
12

Fundamental properties of microbubble
for practical application
1. Increase in interior gas pressure
Pressure
2. Increase in ion concentration
around the gas-water interface
Ions
13

1. Increase in interior gas pressure
Water
Gas
P
P+ΔP
r
Surface tension
Young-Laplace equation
ΔP = 2σ/ r
14

Bubble diameter (μm)
45
40
35
30
25
20
15
10
5
Increase in interior gas pressure
Shrinking over time
Very high pressure
( infinite )
shrinking collapse
0
0 20 40 60
Time (sec)
80 100 120
Diameter ΔP
μm atm
10 0.3
1 3
0.1 30
0 ∞
15

Gas hydrate formation
Gas hydrate = Ice-like material ( with gas molecule )
--- Low temperature / High pressure ---
Normal bubble
( Conventional )
Xe Gas
Comparison
Microbubble
16

Temperature = 3 ºC / 1 Atm.
17

Temperature = 1.1 ºC / 1 Atm.
18

1
Pressure (MPa)
0.1
Hydrate region
Normal bubble
Microbubble
Equilibrium
(Xe Hydrate (1% THF)
-2 0 2 4 Temperature ( ˚C ) 25
Water & Gas
region
Pressure – Temperature diagram of Xe hydrate
19

Pressure
Hydrate region
Micro-bubble &
the surrounding area
. C
. B
A
.
Metastable
region
Water & Gas
region
Equilibrium line
Supercooling limit
Temperature
C
B
A
Nucleation
Micro-bubble
20

5m
Remediation of water environmental by microbubble
1m
Water surface
Bottom
Microbubbles
Transparency: < 2m > 5m
DO: 0 >2mg/L (at the bottom)
Oxygen
Light
aerobic microbes
21

Environmental remediation
Shio-Ashiya Port (Osaka bay area, Japan)
22

Microbubble generator for this test
Power :1.5 kW Water flow : 400L/min. Air supply : 10L/min.
23

The microbubble generator under sea
about 4m from the surface (1m from the bottom)
24

Photograph of the test site
Microbubble generator
(about 4m from the surface)
The stream of microbubbles looks like white smoke
25

Before and after the microbubble treatment
Before / The world of death
(with flash light)
At the bottom of the sea (-5m)
Ascidians
After about 3 months
( without flash light)
A starfish A sea anemone
26

Fundamental properties of microbubble
for practical application
1. Increase in interior gas pressure
Pressure
2. Increase in ion concentration
around the gas-water interface
・Generation of free-radicals
・Generation of Nano-bubble
Ions
27

Electrical property of microbubble
- +
Electrophoresis cell
ζ potential
Smoluchowski’s equation
ζ=ημ/ε
μ: the mobility (m 2 s -1 V -1 )
ε: the dielectric constant (JV -2 cm -1 )
η: the viscosity of water (gcm -1 s -1 )
Surface electricity
Electrical double layers
ψ0
ζ potential
Counter ions
Slipping plane
28

Movement of microbubbles in electrophoresis cell
Electrode
Light Electrode
( + ↔−) (−↔+)
Electrophoresis cell
Microscope
Water + microbubble
29

ζ potential( mV )
ζ potential of microbubble in distilled water
-60
-50
-40
-30
-20
-10
0
10 20 30 40 50 60
Bubble diameter (μm)
30

The relationship between ζ potential and pH of the water
ζ potential (mV)
-140
-120
-100
-80
-60
-40
-20
+20
+40
0
2 4 6 8 10 12
pH
( adjustment by NaOH and NaCl )
31

Na +
OH -
-
OH
Mechanism of bubble electricity
The surface electricity must be caused by
the adsorbed ions at the interface.
H +
OH -
H +
OH -
H +
OH -
OH -
H +
Microbubble
Gas
H +
OH -
OH -
H +
Mg 2+
OH -
Water
Cl
- +
OH and H are adsorbed at the interface
because of a structural reason of water
32

Change in ζpotential of microbubble during collapsing process
ζ-potential ( mV )
-80
-70
-60
-50
-40
-30
-20
-10
0
Condensation
of accumulated ions
Time
0 5 10 15 20 25 30
Bubble diameter (μm)
33

+
Water
+
Free-radical generation by collapsing microbubble
Microbubble
+ +
+ -
-
- -
+ - -
+ +
-
+
+
+
- +
- - +
+
+
+
+
+
+
Accumulated ions
Bubble
→ collapsing
Time
Extinction
of microbubble
Cloud of ions
→ Condensation
Free-radicals
34

Fundamental properties of microbubble
for practical application
1. Increase in interior gas pressure
2. Increase in ion concentration
around the gas-water interface
・Generation of free-radicals
・Generation of Nano-bubble 35

・OH
Measurement of free-radicals by ESR
Spin-trap reagent
DMPO
(5,5-dimethyl-1-pyrroline-N-oxide)
・OH
transient
・OH
DMPO-OH
DMPO
DMPO-OH
stabile
Sampling
DMPO-OH
ESR
(Electron Spin Resonance)
ESR spectrum
36

Free-radical generation during collapsing process of microbubble
A B
C D
37

Experimental setup of radical generation
Water pump
Dissolution
tank
Air
Water
Water tank
Water + microbubbles
Glass
container
DMPO
( spin-trap
reagent )
38
ESR
(Electron Spin Resonance)

ESR spectrum
DMPO-R
1mT
Indicating the generation of alkyl radical
39

Experimental setup of radical generation
Water pump
Dissolution
tank
Air
Water
Water tank
Water + microbubbles
Glass
container
DMPO
+ Acid
(HCl)
40
ESR
(Electron Spin Resonance)

ESR spectrum
1mT
DMPO-OH
Indicating the generation of ·OH (Hydroxyl radical)
41

Experimental setup of phenol degradation
Water pump
Dissolution
tank
Air
Water
Continuous operation
Cooling unit
Phenol
with / without Acid
HPLC
42

Degradation of phenol by collapsing air microbubble
Concentration (mM)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
without acids
with nitric acid
0 30 60 90 120 150 180
Time (min)
43

Ozone
Ozone
The results of ESR test of ozone microbubble
Macrobubble
Microbubble
microbubbles
ESR/
DMPO
ESR/
DMPO
・OH (hydroxyl radicals)
44

Experimental setup of PVA degradation
Water pump
Dissolution
tank
Water
Ozone
Continuous operation
Cooling unit
PVA (Polyvinyl alcohol)
with Acid
TOC
45

Degradation of PVA by ozone microbubble
TOC (mg/L)
400
350
300
250
200
150
Ozone macrobubbles
Ozone microbubbles
Time (min)
+H2O2
0 20 40 60 80 100 120
46

Practical application of collapsing microbubble
Food industry (fishery product) :
(200~300t/day)
COD : 2500~2800mg/L ・OH COD : 800mg/L HEM : tr.
sludge : < 10 t / year
N-Hexane Extractable Material
waste water treatment
Microbubble
Collapsing
( ozone )
Collapse of ozone microbubble
・OH
・OH
47

A phenol factory
To treat waste water from chemical factory
Content Waste water
Phenol 0.32 %
Formalin 0.56 %
Methanol 1.90 %
Acetone 0.08 %
n-butanol 0.03 %
nonvolatile 1.70 %
Not easy to treat by conventional methods
Collapse of ozone microbubble
48

Treatment of waste water from phenol factory
Froth
49

Development of new system to collapse microbubbles
Previous system
water
Gas / ozone
Microbubble
generator
New system
Collapsing microbubble
intentionally
Microbubble
generator
50

Introduction of new collapsing system
51

COD(mg/L)
3500
3000
2500
2000
1500
1000
500
0
Result of the test of microbubble treatment
0 4 8
Time (hour)
12 16
52

Summary
Microbubble
-- Increase in the interior gas pressure
-- Increase in the ion concentration
around the gas-water interface
→ Gas hydrate formation
→ Environmental remediation
Collapse of microbubble
-- Free-radical generation
-- Generation of Nano-bubble
→ Waist water treatment
53

References
1) Takahashi, M. et al. Effect of shrinking microbubble on gas
hydrate formation. J. Phys. Chem. B 107, 2171-2173(2003)
2) Takahashi, M. ζ potential of microbubbles in aqueous
solutions: electrical properties of the gas–water interface. J. Phys.
Chem. B 109, 21858-21864(2005)
3) Takahashi, M. Chiba, K. and Li, P. Free-radical generation
from collapsing microbubbles in the absence of a dynamic
stimulus. J. Phys. Chem. B 111, 1343-1347(2007)
4) Takahashi, M. Chiba, K. and Li, P. Formation of Hydroxyl
Radicals by Collapsing Ozone Microbubbles under Strong Acid
Conditions. J. Phys. Chem. B 111, 11443-11446(2007)