Water Purification by Atmospheric Microplasma Treatment¹Naoto Masamura, ²Marius Blajan and ²Kazuo Shimizu¹Graduate School of Engineering, Shizuoka university²Organization for Innovation and Social Collaboration, Shizuoka University,Jyouhoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

Table.1 Experimental parameters.

Introduction
In recent years, associated with industrialdevelopment, water pollution became
aserious problem. Plasma could be used aswater treatment technology such as
decomposition of organic compound andsterilization of bacteria.
Conventional
technologies
requiresexpensive processes or the usage ofchemicals for water treatment. Microplasma
is an ecological and economical technology
to be applied for water treatment due tothe low cost and low discharge voltage.

Methods
Microplasma Electrode for watertreatment

OHPower supply

ACCarrier gas

Air

Flow rate [L/min. ]2-4

TargetIndigo carmine

Concentration [mg/L]

10Treatment volume [ml]150(2)Photograph of the indigo carmine
solution

A neon transformer was used as the AChigh voltage power supply. Air was supplied
from an air pump as the carrier gas. Itflows in the reactor, pass through theholes of electrodes and generates bubbles.
The position of the electrode at the bottomof the reactor promotes the generation ofactive species in the bubbles andfurthermore the reaction of these active
species with the target to be decompose:indigo carmine diluted in water. The treatedsample was analyzed by UV-VIS, and HPLC.
Fig. 4 show the typical waveform ofdischarge voltage and discharge current.

TargetThecolor
waschangedtransparence
afterthetreatment.

almostplasma(3)HPLC analysis

O*Bubbles

Electrode
Small holes

Fig. 1 Mechanism of water treatment bymicroplasma.
Microplasma electrode was placed under thewater to fit in the plastic container. Air
was flow inside the case to generate insidebubles. Thus surroundings of the electrodewas keeping gas phase due to the carrier
gas.
Various active species such as ozone, OH
radical etc. were generated by microplasma
as shown in Fig. 1[1].

121010Intensity [mAU]

Air12Fig. 4 Typical waveform of discharge
voltage and discharge current.
The spike current was observed at thedischarge rise point. This is the feature ofthe dielectric barrier discharge.

(1) indigo carmine absorbance
0.4

Intensity [a. u. ]0.35
No treatment
3 min.
5 min.
10 min.

0.25
0.2

864864220000.5 1 1.5 2 2.5
Reaction time [min. ]

300.5
1
1.5
2
2.5
Reaction time [min. ]Before treatment

310 min. treatment

Fig. 8 The analysis of component of indigo
carmine by HPLC.
Acetonitrile, ammonium acetate and water
were used as the solvents to separate thecomponent of indigo carmine. The firstpeak is the isatin sulfonic acid and second
peak is the indigo carmine.

Results and Discussion

0.3

Intencity [mAU]

O3Fig. 7 The comparison of the color
between before and after treatment.
Left: before treatment,
Right: after treatment.

After the microplasma treatment, thepeaks of the isatin sulfonic acid increasedthus
indigocarmineconcentration
decreased.

0.15
0.1
0.05
0400Fig. 2 The photograph of the electrode.

Microplasma is a typical dielectric barrierdischarge.

450

500
550600
Wavelength [nm]650700Fig. 5 The analysis of absorbance using
spectrum photometer(Vd=1.9kV).

Microplasma could be used as an ecologicaland economical technology for water
treatment :.

Decrease of 610 nm peak suggests thatorganic compounds contained in indigo
carmine solution was decomposed during
microplasma treatment.

1. Indigo carmine was decomposed after
microplasma treatment. Decomposition
rate was improved to 61% with theincrease of the treatment time.

Experimental Setup

2. The decomposition rate depends on thegas flow rate which determines thebubble size and quantity and furthermore
affects the indigo carmine.

Oscilloscope
Current
probe
UV-VISHVHPLCHV probe
IndigoFlow meterConclusions

carmineBubbles

ElectrodeFig. 3 An experimental setup.

Fig. 6 Chemical reaction of indigo carmine
by microplasma treatment.
IndigocarminehastheH
type
chromophoric group which gives the bluecolor. Double bond (C=C) was cut thus OH
radicals and ozone presence lead to theformation of a new bond 2(C=O). As aresult, Indigo carmine was decomposed toisatin sulfonic acid.

3. HPLC analysis showed that thedecrease of the indigo carmine peak wasstrictly correlated with the increase of
the isatin sulfonic acid peak due to themicroplasma treatment.

Reference[1] K. Takahashi, Y. Sasaki, S. Mukaigawa, K.
Takaki, IEEE, Trans. on Plasma Sci. Vol.
38, pp. 2694-2699(2010).