Basic study of water treatment by
low discharge in the bubbled water
S. Muramatsu, T. Sonoda, M. Blajan, K. Shimizu,Innovation and Joint Research Center, Shizuoka University,
3-5-1 Johoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

INTRODUCTIONRESULTSThe current water treatment technology
has some problems such as chemical
restriction. Therefore, we carried out thediscoloration of indigo carmine solution
and inactivation of Escherichia coli bydischarge in water below 10 kV, which
is not used chemicals.

(1) Electric characteristicsOzone generation
Air5 kV

O2100 ns
GND5A100 ns

GNDMETHODS(1) Discharge in water

Discharge voltage 7.8 kV

O2 + e → O(3P) + O(3P) + eDischarge current 5.8 A
Pulse widthWater

1μs

O(3P) + O2 + M → O3 + M

electrodes(2)Discoloration of indigo carminesolution

HO2*OH

UVstreamer

O3

Environment load of discharge in water islittle since chemicals are not used.

AirO2

Image of discharge in water

When O2 is supplied to the solution,
dissolved ozone concentration was
25 % higher compared with air. At adischarge time of 60 min, thedissolved ozone concentration of0.15 mg/L with O2, 0.12 mg/L with air
was obtained.
(3) Inactivation of E. coli

N2TheElectrodes

initial concentration of indigo
carmine solution was about 10mg/L.
When the discharge voltage was 45 minwith O2, the concentration dropped to 0mg/L.

N2O2
Air

Analysis by UV spectrophotometer
O2
O2
O2

Bubbles with brightly discharges areobserved.

O2O2(2) Experimental setup

Image of E. coli treated samples

A pulse voltage supply
Neon transformerAC 100V

Spark gap switch

2 kΩ
1.0 kΩ

1.１ nF

Pulse voltage is used for discharge inwater to prevent temperature rise by joule
effect and electrolysis.

The peak of 611 nm, which is indigo
carmine solution decrease with theincrease in discharge time.
Analysis by HPLCUVSpectrophotomet
erOzonemeter

HV voltage probe

Airpump

Electrodes probe
Current

Flow
meter

Beforetreatment

Discharge time is 5min

Indigo carmine
IndigocarmineExperimental setup for discoloration ofindigo carmine solution

HPLC

A shorter period of time was necessary
for the complete inactivation of E. coli
when Air or O2 was used to bubbled inwater.

BeforetreatmentAir60 min

Discharge time is 10min

Discharge time is 15min

Gascylinder

Indigo carmine
OscilloscopeDry air, nitrogen, and oxygen aresupplied by using an air pump and gas
cylinders. The concentration of indigo
carmine solution is analyzed by HPLCand UV spectrophotometer. Dissolved
ozone concentration is measured byozone monitor.
Experimental setup for inactivationof E. coli

Indigocarmine
O260 minDischarge time is 20 Discharge time is 25minminN260 min

The water treatment performances
improve when gas containing O2
was added to discharge area.
Photograph of the indigo carmine
solutionO2 supply
100 % inactivation after 20 min

CONCLUSIONS
The following conclusions were obtainedby the series of experiment by using
discharge in bubbled water.
①Indigo carmine was degraded by low
voltage discharge below 10 kV in
bubbled water.
10 mg/L → 0 mg/L
discharge time was 45 min with O2

O260min

Inactivation effect of discharge in water
was inspected by comparing the numberof colonies with and without discharge.

Air60minN2Before
60min treatment

The color of indigo carmine solution wasbrighter, especially when O2 or Air wassupplied while discharge.

②E. coli was 100% inactivated by low
voltage discharge below 10 kV in
bubbled water.
discharge time was 20 min with Airand O2③ The water treatment performances
improve when gas containing O2 isadded to discharge area. This result
could be the effect of the generation ofactive radical species and ozone.