Krypton chlorine excilamp for escherichia coli inactivation
in aqueous media
Bouabdellah RAHMANI1, El roumaissàa RAHMANI2, Georges ZISSIS3 , Svetlana Avtaeva4, B. Saghi1
1
University of science and technology, Oran, Algeria, [email protected]
2
Saliege- 3 rue Bernanos. BP 33130-31131-Balma-Cedex , erahmani@saliége.fr
3
Université de Toulouse 3; UPS, INPT; LAPLACE (Laboratoire Plasma et Conversion d'Energie);
[email protected]
Kyrgyz-Russian Slavic University, Bishkek, Kyrgyz Republic, [email protected]
4
1. Introduction
Excilamps can be considered as attractive alternatives
to mercury lamps and lasers for applications in
microbial-control technologies because of the absence
of elemental mercury, long lifetime, geometric
freedom, high photon flux and moderate operating
temperatures [1]. The ultraviolet excimer sources have
been
developed
[2-5]
for
inactivation of
microorganisms [6-9] depending on their wavelength
and their intensity. The inactivation is caused by
changing absorption degrees of different biomolecules
such as DNA, membranes or proteins. According to
the kind of chemical bond between the elements of
biomolecule, the UV light energy is absorbed by the
element at different wavelength in a selective way. The
low pressure (LP) mercury lamp emitted at 254 nm is
traditionally used for inactivation of microorganisms
[8]. This lamp emits near the DNA peak absorption
coefficient at 265 nm [10]. This absorption causes
damage to DNA by altering nucleotide base paring,
especially 6_4 photoproducts and thymine dimers
formation [11]. If the damage remains not repaired, the
transcription and the replication of DNA are blocked.
These processes lead to cell death. The proteins show a
strong absorption coefficient at 220 nm [12, 13], which
is an alternative way to reduce the photoreactivation
mechanism. This mechanism uses a single enzyme
called photolyase to repair UV-induced damage in the
DNA [14 ]. The photoreactivation causes problems
especially for large-scale use of UV inactivation of
microorganisms when processing treated wastewater,
drinking water and sewage are exposed to sunlight. In
contrast our excilamp krypton-chlorine shows a
relatively sharp emission spectrum with a peak at 222
nm targeting the proteins of microorganism. The aim of
this work was to examine the inactivation efficiency of
the pulsed dielectric barrier discharge excilamp KrCl
[5] against the E. coli bacteria which is commonly used
as a biological indicator for disinfection efficiency in
water systems
2 Materials and methods
2.1 Bacterial strains and incubation conditions
The basic solution of the E. coli was obtained by
incubating a few colonies (2 to 3) of the strain E. coli
(O157:H7) in 5ml of the liquid LB (Luria Bertani)
nutrient under the incubation conditions at 30°C and
for 20 hours. The pH of this solution was adjusted at
7.2 by NaOH. A volume of 1ml taken from this
solution was diluted with 9 ‰ of saline until 10-6 for an
easy visual counting of the E. coli. The initial density
was estimated by taking 10l from the diluted solution
at 10-6 in a sterilised circular Petri dish under the same
incubation condition cited above. Its value of 34.10 6
CFU/l was obtained by averaging three values
receiving the same dose. A volume of 10 l taken from
the basic solution for the aqueous media was irradiated
in an open Petri dish. We add 2 ml of the liquid LB
nutrient to the irradiated aqueous media before its
incubation phase. The Petri dishes were covered by the
aluminium foil just after irradiation to avoid the
photoreactivation mechanism.
2.2 UV excilamp
The pulsed DBD excilamp krypton chlorine [5] was
used for the inactivation of the Escherichia coli
bacteria. The spectrum of this excilamp shows an
intense peak at 222 nm (KrCl*) and a weak one at 258
nm (Cl2*). The excilamp was oriented horizontally on
the opened glass Petri dish with a diameter of 40 mm
and a height of 10 mm.
2.3 Irradiation and evaluation of the results
The E. coli has been irradiated in two different medias
at the distance of 30 mm and 26 mm from the UV wall
source [5], respectively. We use irradiation in the
aqueous and on the surface medias. This distance was
chosen for reducing the excilamp thermal effect on the
E. coli bacteria during the irradiation. We used nine
doses for each media. The photoreactivation
mechanism was minimized by covering each irradiated
Petri dish with the aluminum foil before and after the
UV irradiation. The UV dose expressed in mJ/cm 2 is
the result of the product of an irradiating time in s and
the excilamp irradiance in mW/cm 2. The logarithmic
reduction factor log (N/N0) of the E. coli was
calculated by averaging the values of three Petri dishes
receiving the same dose. The E. coli population N0 and
N in CFU/l denotes their density values before and
after the UV irradiation, respectively.
Table 1: Survival E. coli density on dose in aqueous media.
Time (s)
3 Results and discussion
The results on the inactivation of the Escherichia coli
in the aqueous media are presented in figure 1. It
shows a logarithmic reduction factor of 5.1 log in
concentrations of the E. coli within irradiation time of
30 s at the dose of 180 mJ/cm2. That means only 268
CFU/l of the E. coli are resistant at the wavelength 222
nm as shown in table 1.
Figure 1 : Logarithmic reduction factor of E. coli on dose at
222 nm in aqueous media
Survival E. coli density
(CFU/l)
In aqueous media
268
186
162
141
138
101
107
107
102
References
-5,0
Logarithmic reduction factor log(N/No)
30
60
120
180
240
300
360
420
480
Dose
(mJ/cm2)
180
360
720
1080
1440
1800
2160
2520
2880
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