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Disinfection of Legionella pneumophila by ultrasonic
treatment with TiO
2
Mahmoud Farshbaf Dadjour
a
, Chiaki Ogino
b
, Susumu Matsumura
b
, Shinichi Nakamura
c
,
Nobuaki Shimizu
a,
Ã
a
Division of Biological Measurement and Applications, Institute of Nature and Environmental Technology, Kanazawa University,
Kanazawa, 920-1192, Japan
b
Department of Chemistry and Chemical Engineering, Kanazawa University, Kanazawa, 920-8640, Japan
c
Department of Bacteriology, Graduate School of Medical Science, Kanazawa University, Kanazawa, 920-8640, Japan
article info
Article history:
Received 23 June 2005
Received in revised form
26 December 2005
Accepted 28 December 2005
Keywords:
Disinfection
Legionella
Ultrasound
Titanium dioxide
Hydroxyl radical
ABSTRACT
An ultrasonic treatment system, using a TiO
2
photocatalyst, was used to disinfect Legionella
pneumophila. A kinetic study of the process indicates that TiO
2
significantly improves the
disinfection process. The concentrations of viable cells were reduced to 6% of the initial
concentrations in the presence of 0.2 g/ml TiO
2
after a 30 min of treatment period, while
only an 18% reduction was observed in the absence of TiO
2
. The potency of the disinfection
could be enhanced, to some extent, by increasing the amount of TiO
2
used. Cell
concentrations were decreased by an order of 3 within 30 min of treatment in the presence
of 1.0 g/ml TiO
2
. The disinfection power in the presence of TiO
2
versus Al
2
O
3
was also
compared and the findings showed that TiO
2
induced a higher cell killing. No significant
effect of initial cell concentration on the disinfection was found in the range of 10
2
–10
7
CFU/
ml after a 30 min of treatment period. The mechanism of cell killing was investigated by
examining the effects of OH radical scavengers such as ascorbic acid, histidine and
glutathione. The disinfection power was reduced in samples that contained these radical
scavengers, thus indicating the importance of OH radicals.
& 2006 Elsevier Ltd. All rights reserved.
1. Introduction
A number of outbreaks of Legionnaires’ disease at hospitals
and industrial facilities has been reported (Fraser et al., 1977).
It is well known that Legionella bacteria cause these diseases
through the inhalation of aerosols from contaminated water
systems (Baskerville et al., 1981). Water systems, such as
cooling towers, bathtubs and hot springs are generally
thought to be major sources of these bacteria. A variety of
chemical or physical methods such as chlorination, ozona-
tion and germicidal lamps (UV) have been developed for
treating the sources of such types of bacteria (Evora and
Kavarnos, 1999; Franzin et al., 2002; Kim et al., 2002; Lin et al.,
1998; White, 1992; Yamagiwa et al., 2001, 2002).
An ultrasonic system has also been used as an alternative
method of disinfection and has been used for the oxidation of
contaminants in water as well as for cell inactivation (Hua
and Thompson, 2000; Ollis et al., 1991). The optimization of
ultrasonic treatment as an advanced oxidation technology
and its application has been reported (Hua and Hoffmann,
1997). During the ultrasonic treatment of aqueous solutions
acoustic cavitations are created as the result of the growth
and adiabatic collapse of bubbles in the liquid. As a result of
cavitational bubble implosions, extreme temperatures and
pressures are generated at the center of the collapsed bubble,
leading to the dissociation of water molecules (Suslick, 1990).
It is noteworthy in this regard, that the production of hydroxyl
(OH) radicals, hydrogen peroxide and other oxidants have
ARTICLE IN PRESS
0043-1354/$ - see front matter & 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.watres.2005.12.047
Ã
Corresponding author. Tel.: +81 76 234 4807; fax: +81 76 234 4829.
E-mail address: nshimizu@t.kanazawa-u.ac.jp (N. Shimizu).
WATER RESEARCH
40 (2006) 1137– 1142