22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Preliminary study of needles-to-plate plasma dedicated to the drug residues
treatment
O. Aubry, H. Rabat, Y. Baloul and D. Hong
GREMI, UMR 7344, CNRS / Université d’Orléans, France
Abstract: Optical and electrical characteristics of a Dielectric Barrier Discharges produced
in contact with an aqueous liquid have been studied. The high-voltage pulsed discharges
were performed in oxidative gases used to remove pollutants as drug residues in liquid
effluents. Optical emission spectra of the discharge were acquired in needles-to-plate non
thermal atmospheric pressure plasma and analysed in the UV-visible spectral range.
Keywords: non-thermal plasma, optical emission spectroscopy, liquid
1. Introduction
In the recent decades, the interest in the application of
non-thermal atmospheric pressure plasma (NTP)
technology for aqueous pollutants abatement has been
highly increased. It is well known [1-4] that NTP are
innovative Advanced Oxidation Processes (AOPs) to
produce highly reactive species (OH, O, H 2 O 2 , etc.). NTP
can be successfully applied for the treatment of organic
molecules [3] and pharmaceutical compounds in liquid
effluents [5]. Many configurations of the discharges can
be done; i.e. discharges at the upstream or in contact with
the liquid [1,3,5]. In direct liquid-discharge contact, the
UV radiation and the oxidizers species act effectively on
complex chemical compounds (as drug residues in liquid
effluents) or on a biological bulk in function of the
operating conditions. In this paper, we present a
preliminary study on the application of Dielectric Barrier
Discharges to treat drugs residues in liquids. The
operating conditions plays a role on the behaviour of the
discharges and then on the efficiency of the plasma
process to treat liquids. Here, our experiments are
dedicated to optical and electrical diagnostics of the
discharge.
2. Experimental set-up
Figure 1 displays a schematic diagram of the
experimental device used.
Fig. 1. Schema of the apparatus device for optical
emission spectroscopy of the discharges.
The plasma reactor is a needles-to-plate reactor. The
gap between the tip of the needles and the liquid can be
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varied from 0 to several mm.
generated at atmospheric pressure.
The discharges are
The lower electrode is a copper plate deposited on an
epoxy plate which is the dielectric. This latter side is in
contact with the liquid. The inlet gas is injected through
the upper electrodes (needles) which are capillaries (inner
diameter is 0.5 mm). The discharges are generated at the
tip of the needles above the liquid (Fig. 2).
Fig. 2. Photo of 6 discharges above the liquid.
The high-voltage is powered by a TTI function
generator (TG4001) and a high-voltage amplifier (Trek
20/20C). The effects of the electrical parameters (applied
high-voltage (4-5 kV) and the frequency (50 Hz-2 kHz))
on the discharges are studied. The electrical
measurements are performed using high voltage
(PE20KV Lecroy) and current (CT-C5 Magnelab) probes
and displayed on a DPO 3054 Tektronic oscilloscope.
One of the interests of our plasma device is the
capability to light-on above the liquid only one needle or
up to twelve ones. Thus, we can study the effects of the
number of discharges on the liquid treatment and on the
behaviour of the discharges. The number of discharges
implemented implies a change of the conversion rate of
the pollutant in the liquid and the products (nature and
concentration). The liquid volume (up to 80 mL), the gas
flow composition (Air, Air+Ar, O 2 +N 2 ...), the flow rate,
the high-voltage parameters (high voltage pulse,
repetition rate...), the liquid nature (pH, conductivity)
affect also the produced species in the discharges. The
study of these parameters and their influence will allow us
to obtain a better understanding of the applied process and
an enhancement of the treatment efficiency in terms of
energy cost, produced species and conversion rate.
1
Fig 4. Photos of discharge produced at a tip of a needle
with an argon flow in air: a) single streamer and b)
multiple streamers (12 electrodes configuration;
needles-liquid gap = 4 mm;).
In figures 5, we show the discharge produced in air with
or without Ar flow rate through the electrode in the single
needle configuration. Changes on the discharge are
observed in comparison to the experiments in the multielectrodes configuration. For example, with Ar flow, there
is a modification of the discharge near the liquid (Fig 5b).
This behaviour is linked to the periodic currents peaks.
This change is not observed for other injected gas. A full
study on this behaviour will be studied and presented in a
later paper.
4 mm
3. Results
Figures 3, typical waveforms of voltage and current are
displayed when the discharge occurs in air (Fig. 3a) and
in air with a flow of Ar in the electrode (Fig. 3b). Only in
this latter case, we observe periodic current peaks in
positive voltage times (fig 3b). In air or with another gas
flow in the needles (air, O 2 , N 2 ), the periodic current
peaks are not observed.
a) in air
a) In air
b) In air + Ar
Fig 5.
Photos of the discharge in one electrode
configuration. a) in air; b) in air + Ar (10 sccm) in the
needle. (electrode-liquid gap=4 mm; exposure time=4ms).
b) in air + Ar
Fig. 3. Typical voltage and current waveforms.
Time-resolved ICCD images of one discharge are
presented in a 12 needles configuration reactor (Figures 4)
and in a single needle configuration (Figures 5).
In the single electrode configuration, optical emission
spectroscopy (OES) has been performed. In our
experiments, we can detect the species produced as
OH, N 2 , Ar, O 2 , N 2 , N 2 +,... in function of the inlet gas.
Examples of obtained spectra are displayed in Fig 6.
a) in air
a) Single streamer in
negative voltage time
2
4 mm
4 mm
In figures 4, time-resolved images of the discharge are
presented in function of the high-voltage times with Ar
flow injected through the needles. Fig 4a displays the
discharges in the negative voltage times; the discharges
correspond to a single streamer produced at each needle
tip. In the positive high-voltage times (fig 4b), several
streamers can be produced from the tip of the electrodes.
In this case, these streamers seem to be correlated to the
current peaks observed in figure 3b.
b) Multiple streamers
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b) in air + Ar
[6] S. Pellerin, J. M. Cormier, F. Richard, K. Musiol, J.
Chapelle, Journal of Physics D: Applied Physics, 29(3),
726 (1996).
[7] http://www.specair-radiation.net/index.php
Fig. 6. Optical emission spectroscopy spectra.
Optical emission spectrometry shows that an injection
of Ar modifies the produced species in the discharge and
the temperature of the discharge. In first approximation,
we can determine the rotational temperature, Tr, of the
discharge by comparing the experimental spectra and
synthetic ones given by Pellerin et al. [6]. Thus, the
relative intensities of OH lines depend on Tr. This give us
a rotational temperature lower than 3000 K for both cases
studied. To obtain more detailed temperatures of our
discharges, a fitting of the experimental spectra are also
performed (not presented in this abstract) using OH, N 2 ,
O 2 emission spectra. Simulation spectra are obtained with
SPECAIR software [7]. The fitting of the simulated
spectra with the experimental ones give us information on
rotational, vibrational and electronic temperatures for the
studied discharges in function of the operating conditions.
5. Conclusion
The main of this preliminary study is to obtain a better
understanding of the discharge applied to the treatment of
drug residues in a liquid. One observe that the operating
conditions (applied voltage, pulse repetition rate,
electrodes-liquid gap, gas flow nature) highly affect the
discharges behaviour (current peaks, streamers changes)
and the nature of the species generated in the plasma
which will affect the efficiency of the liquid treatment.
6. Acknowledgments
This work is partially funded by Région Centre,
(TREMEMAP project).
7. References
[1] P. Bruggeman, C. Leys, Journal of Physics D:
Applied Physics, 42, 053001 (2009).
[2] M. Arif Malik, Plasma Chemistry and Plasma
Processing, 30, 21, (2010)
[3] B.R. Locke, International Journal of Plasma
Environmental Science and Technology, 6, 3, 194
(2012).
[4] B. Jiang, J. Zheng, S. Qiu, M. Wu, Q. Zhang, Z. Yan,
Q. Xue, Chemical Engineering Journal, 236, 348 (2014).
[5] M. Magureanu, D. Piroi, N.B. Mandache, V. David,
A. Medvedovici, V.I. Parvulescu, Water Research, 44,
11, 3445 (2010).
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