Study of Wastewater Purification by Atmospheric Microplasma
Naoto Masamura, Marius Blajan and Kazuo Shimizu
Organization 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 and Mechanism

Power supplyACCarrier gas

Air

Flow rate [L/min. ]10TargetIndigo carmine

Concentration [mg/L]

10Treatment volume [ml]200

A neon transformer was used as the AChigh voltage power supply. The carriergases were supplied in case of the air froman air pump and in case of N2, Ar and O2
from gas cylinders. It flows above thereactor and pass through the holes ofelectrodes. Indigo carmine was used as thetarget to be decomposed. The treatedsample was analyzed by UV-VIS, ozone
monitor and ESR(Electron Spin Resonance).

(3)Decomposition rate ofindigo carmine

Fig. 7 Ozone concentration in gas phase.
The decomposition rate was higher than
40% at discharge voltages 1.0-1.3 kV.

(4)ozone concentration

Results(1) Observation ofindigo carmine absorbanceFig. 8 Ozone concentration versus
discharge voltage measured in gas phaseand liquid phase by microplasma.

Microplasma electrodes are perforated
metallic plates covered with a dielectric
layer and faced together with a spacer of
100 μm as shown in Fig. 1.
Microplasma electrodes were placed at small
distance above the water thus gas is flown
towards the water surface to react withthe target to be decomposed. Various active
species such as ozone, OH radical etc. weregenerated by microplasma[1].

Fig. 4 The analysis of absorbance using
spectrum photometer(Vd=1.0 kV).
The decrease of 610 nm and 300 nm
peaks suggest that organic compounds
contained in indigo carmine solution wasdecomposed during microplasma treatment.

The ozone concentration increased with
the increase of the discharge voltage. 0.52.2% of the total ozone generated in gas
phase was dissolved in water.

(5)ESR analysis
200000150000Intensity[a.u.]

Fig. 1Mechanism of water treatment bymicroplasma.

10000050000
03400-50000

3425

3450

3475

3500

-100000-150000

Fig. 5 Chemical reaction of indigo carmine
by microplasma treatment.

Fig. 2 The emission during discharge(Vd=1 kV).

Microplasma is a typical dielectric barrierdischarge. The image of microplasma
discharge is shown in Fig. 2.

Indigocarmine
hastheHtype
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.
(2) Decomposition rate forvarious career gases
60

Decomposition rate [%]Experimental Setup
Oscilloscope
Currentprobe

Flow meter

503020Air pump

HV probe

0O2

UV-VISElectrodes

ESR
mg/L

Indigo carmine
solutionppm

Water pumpOzone monitor

Fig. 3 An experimental setup.

Magnetic field[G]Fig. 9 OH signal detected by
an ESR measurement
Spin trap agent 5,5-dimethyl-1-pyrroline
N-oxide was used to perform ESR analysis.
Generated OH radical by microplasma wereobserved at 3445, 3460, 3430, 3475
gauss.

Conclusions

Microplasma could be used as an ecologicalandeconomicaltechnology.
Watertreatment using microplasma was carriedout.
1. Indigo carmine was decomposed after
microplasma
treatment
anddecomposition rate increased with thetreatment time and discharge voltage.

40

10HV-200000

AirArN2Fig. 6 The decomposition rate of indigo
carmine for various career gas(Vd=1.00kV)
Fig. 6 shows the decomposition rate wascalculated by the absorbance value. Air andoxygen were higher due to the active
species of oxygen origin.

2. OH radical was one of the causes ofindigo carmine decomposition. It wasdissolved in the water as confirmed byusing ESR.
3. 0.5-2.2% of the ozone generated in gas
phase was dissolved in water.

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