Characterization of Multiple Bubble Jet with Pulsed Discharge
for Water Treatment
Hideya Nishiyama1, Ryosuke Nagai2, Kei Niinuma2 and Hidemasa Takana1
1 Institute of Fluid Science, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan
2 Graduate School of Engineering, Tohoku University, 6-6-04, Aramaki Aza Aoba, Aoba-ku, Sendai, 980-8579,
Japan
Abstract: The characteristics of multiple argon bubble jet in which streamer is
generated by DC pulsed discharge, has been experimentally clarified through the
discharge visualization in a bubble, decolorization of methylene blue solution
and decomposition of acetic acid solution. There is complex streamer behavior in
a bubble jet in which discharge propagation is along the interface of bubble. O
radical and OH radical during streamer discharge in Ar, O2 and air bubbles are
confirmed by spectroscopy measurement. Finally, methylene blue solution and
acetic acid solution are successfully decomposed by these radicals in a DC
discharge multiple bubble jets.
Keywords: streamer, bubbled plasma, radicals, water treatment
1. Introduction
Water treatment technology using O3 has been used
extensively due to its long life time and its
oxidization so far [1]. However, it is not easy to
decompose persistent harmful substances using O3.
Recently, advanced water treatment
technology using electrical discharge in gas-liquid
two phase flow has been intensively paid attention to
decompose persistent harmful substances by O and
OH radicals [2-3]. The direct O radical and OH
radical injection method into the solution produced
by the streamer discharge inside bubbles is very
effective to improve the decomposition efficiency in
liquid, because they have very short life time and
strong oxidization in atmospheric air and oxygen [46]. Then, it is very important to clarify the all
correlations among the discharge structure in the
bubble, bubble jet dynamics and the decomposition
characteristics synthetically.
In the present paper, multiple bubble jet
system encapsulating O radical and OH radical
generated by DC pulsed discharge in the small
bubbles is successfully constructed for methylene
blue solution and acetic acid solution decomposition.
Multiple bubble jet behavior with luminescence and
complex streamer behavior in a bubble [7] are
successfully visualized to detect the radicals for
advanced oxidization process. The decolorization of
methylene blue solution is effectively confirmed by
using multiple Ar, O2 and air bubble jets with O and
OH radicals.
Finally, the acetic acid solution is
successfully decomposed by this system for short
time.
2. Experimental Apparatus and Measurement
Figure 1 shows a schematic illustration of
experimental set up. The gas feeding vertical quartz
tube has 6.0 mm outside diameter and 4.0 mm inside
diameter. It has 5 holes with 0.5 mm inside diameter
in line on the tube side wall with 10 mm spacing to
generate the multiple bubble jet. There are grounded
cylindrical tungsten cathode with 3.0 mm diameter
inside the quartz tube and copper anode with applied
high voltage at the bottom of reactor. The feeding
gas is argon, oxygen and air with 4.0 Sℓ/min and the
solution is water with 0.55 ℓ. The electrical
conductivity of pure water is 300 µS/m. The
applying DC pulsed voltage is 6 kV and 1000 Hz.
The high speed camera is used to visualize the
dynamic behavior of bubble jet with streamer
discharge. The expose time is 20 µs. The spectroscopy
is used to detect the reactive chemical species inside
(a) t = 1060 µs
(b) t = 2060 µs
Figure 2. Photos of bubbles with streamer discharge.
3. Experimental Results and Discussion
Figure 1. Schematic illustration of experimental set up.
and around multiple bubble jet with streamer
discharge. The decolorization test for methylene
blue (1.0 mg/ℓ) is conducted by measuring absorbed
emission at 660 nm every 2 and 5 min under
bubbling. Furthermore, the decomposition test for
acetic acid solution is conducted by measuring the
reproduced CO2 concentration after 10 min bubbling
with discharge.
Figures 2 (a) and (b) show the ejected Ar bubble
behavior with streamer discharge. The flow rate of
Ar is 100 Smℓ/min. The time zero means start of
taking picture. The streamer propagates inside the
interface of bubble [7]. The interface of bubble
changes its shape and is collapsed by continuous
streamer discharge with ejecting some microbubbles
outside of interface of bubbles.
Figures 3 (a) – (d) show the time evolution
of decolorization of methylene blue solution by
multiple argon bubble jet system with discharge.
The flow rate of argon is 4.0 Sℓ/min. The
decolorization is completely achieved in 30 min by
O radical and OH radical in the spectroscopy
measurement.
(a) 0 min
(b) 10 min
(c) 20 min
(d) 30 min
Figure 3. Decolorization of methylene blue solution by argon bubble jet with streamer discharge.
100
V = 6 kV
f = 1000Hz
2.5 Sl/min.
1.0 Sl/min.
Air bubble jet
QAir = 4.0 Sl/min.
80
Concentration (%)
Ar bubble jet
QAr = 4.0 Sl/min.
60
2.5 Sl/min.
1.0 Sl/min.
O2 bubble jet
QO2 = 4.0 Sl/min.
40
2.5 Sl/min.
1.0 Sl/min.
20
0
10
20
30
(a) with discharge
t (min.)
Figure 4. Time evolution of normalized concentration of
methylene blue solution for various flow rates.
Decomposition efficiency (mg/kJ)
0.3
[8]
Micro bubble jet
Pressurizing dissolution method
with UV254
without UV254
O2
Venturi method
0.2
with UV254
without UV254
Ar
0.1
Air
0
1
2
3
Qgas (Sl/min.)
4
5
Figure 5. Decomposition efficiency as a function of flow rate.
Figure 4 shows the time evolution of
normalized concentration of methylene blue solution
for various flow rates. 100 % means the
concentration just when discharge starts. The
concentration decreases in exponential manner with
time. The decolorization of methylene blue is the
furthest for oxygen bubble jet. The second
decolorization rate and third one are by using argon
bubble jet and air bubble jet, respectively. The
decolorization is rapid at larger flow rate for all
multiple bubble jets. This is due to active mixing of
methylene blue solution and much productions of O
radical and OH radical.
Figure 5 shows the decomposition efficiency
(b) without discharge
Figure 6. Concentrations of carbon dioxide through
decomposition of acetic acid solution by argon bubble jet with
or without discharge
as a function of flow rate. The decomposition
efficiency is defined as the decomposed quantities
for per unit input electrical power. The power used
for decolorization of methylene blue is ranged from
10 W for oxygen and argon, to 30 W for air bubble
jet, respectively. The decomposition efficiency is the
largest for oxygen bubble jet, the second one and the
third one are for argon bubble jet and for air bubble
jet respectively. This is because the required input
power to produce and sustain plasma is the largest
for air bubble jet due to higher dissociation energy
of nitrogen molecule. The decomposition efficiency
for argon bubble jet is comparable to that for ozone
microbubble jet coupled with UV irradiation [8].
Figures 6 (a) (b) show the reproduced CO2
qualitative concentration by decomposing acetic acid
solution inside the Ar multiple bubble jets with and
without streamer discharge, respectively. When the
acetic acid solution is decomposed by multiple
bubble jets with streamer discharge, the
concentration of CO2 increases by 100 ppm. The
chemical decomposition process is shown here.
CH3COOH + ・OH → CH3C(O)・+ H2O
→ CO2 + ・CH3 + H2O
(1)
This means that it is possible to decompose the
persistent harmful substance by using multiple
bubble jets coupled with O radical and OH radical.
On the other hand, acetic acid cannot be
decomposed by air and oxygen multiple bubble jets
with discharge.
4. Conclusions
The bubble jet behavior with streamer discharge is
clarified relating to the discharge propagation in a
bubble the production of O radical and OH radical,
and
microbubble
generation.
Furthermore,
decomposition characteristics of methylene blue and
acetic acid solution are also clarified through
decomposition efficiency and reproduction of CO2.
The results obtained in the present study are as
follows.
(1) There is complex streamer propagation inside
the interface of bubble. The interface of bubble
is deformed and is collapsed, which results in
the generation of microbubbles.
(2) The decomposition efficiency of methylene
blue is the highest for oxygen microbubble jet.
(3) The acetic acid solution can be decomposed by
argon microbubble jet utilizing O radical and
OH radical.
Acknowledgements
This work was partly supported by GCOE program
Grant, World Center of Educational and Research
for Trans Disciplinary Flow Dynamics (2010). We
would like to give our sincere thanks to Mr. K.
Katagiri and Mr. T. Nakajima for their technical
supports.
References
[1] M. Takahashi, K. Chiba and P. Li, “Formation
of hydroxyl radicals by collapsing ozone
microbubbles and strongly acidic conditions”, J.
Physical Chemistry, Series B, 111-39, 1144311446 (2007).
[2] H. Katayama, H. Honma, N. Nakagawara and K.
Yasuoka, “Decomposition of persistent organics
in water using a gas-liquid two-phase flow
plasma reactor”, IEEE Trans. Plasma Sci. 37,
897-904 (2009).
[3] K. Sato, K. Yasuoka and S. Ishii, “Water
treatment with pulsed plasmas generated inside
bubbles”, IEEJ. Trans. FM, 128-6, 401-406
(2008).
[4] M. Kurahashi, S. Katsura and A. Mizuno,
“Radical formation due to discharge inside
bubble in liquid”, J. Electrostatics, 42, 93-105
(1997).
[5] T. Miichi, N. Hayashi, S. Ihara, S. Satoh and C.
Yamabe, “Generation of radicals using
discharge inside bubbles in water for water
treatment”, Ozone Science & Engineering 24,
471-477 (2002).
[6] A. Yamatake, J. Fletcher and K. Yasuoka,
“Water treatment by fast oxygen radical flow
with dc-driven microhollow cathode discharge”,
IEEE Trans. Plasma Sci. 34, 1375-1381 (2006).
[7] N. Yu. Babaeva and M. J. Kushner, “Structure
of positive streamers inside gaseous bubbles
immersed in liquids”, J. Phys. D: Appl. Phys.
42, 132003 (2009).
[8] T. Shibata, A. Ozaki, H. Takana and H.
Nishiyama, “Water treatment characteristics
using activated air microbubble jet with
photochemical reaction”, J. Fluid Sci. & Tech.
8-2, 242-251 (2011).