Tratamiento de eliminacion de biofilm

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Inactivation rates of the biofilms of P. fluorescence and
P. aeruginosa established on a small slide glass in ozone
water (0.9–3.2 mg/L, 1–20 min) were determined in a
batch or flow-through system. The effects of ozone water
on the biofilm matrices were defined clearly in situ by
confocal laser scanning microscopy. These results indicate
that ozone is an effective biocide against biofilmsand it can
remove exopolysaccharides in the biofilm matrices. However,
the effective concentration of ozone for disinfection of
biofilms varied with the biofilms formed, mainly due to
reactions of ozone with constituents of the biofilms.
Keywords Ozone, Disinfection Efficacy, Biofilms, P. fluorescens,
P. aeruginosa, Removal, Extracellular Polysaccharides

INTRODUCTION

The disinfectionand removal of biofilms has become
an important subject in maintaining water quality management
in the fields of swimming pools, food processing
lines, industrial water systems, etc. Microorganisms, by
attaching to surfaces to form biofilms which are protected
by matrices of excreted exopolysaccharides (EPS), are
usually highly resistant to antimicrobial agents. The
importance of tests usinga biofilm system has been
pointed out in order to evaluate disinfection efficacy of
biocides (LeChevallier et al., 1988a and Wright et al.,
1991). We have attempted to establish a simple method
of producing microbial biofilm from ubiquitous bacteria,
Pseudomonas fluorescens, Pseudomonas aeruginosa and
Klebsiella pnuemoniae in water environments and in
biofilms, and compared the efficacy ofseveral halogen
biocides using the biofilms established. By using confocal
laser scanning microscopy (CLSM), differences in cell
density and structure among the biofilms established were
visualized clearly, and the changes of biofilm structures
caused by halogen biocides were described (Tachikawa
et al., 2005).

Although ozone water is widely used as a potent
oxidant in water treatments(White, 1999), the efficacy
of ozone water for biofilm disinfection remains to be
established. Thomas et al. (2004) studied the resistance
of the amoebae, Legionella pneumophila, and biofilms of
b-proteobacteria to disinfection treatments with ozone,
chlorine dioxide, chlorine, etc. in pilot-scale domestic
water systems. Planktonic and biofilm populations in
the systems were reducedmarkedly, but they were still
detectable after ozone treatment at 0.5 mg/L, which
decreased to the undetectable limit (7, ozone also can react nonselectively or
indirectly through HO radicals formed by the hydroxyl
ion-catalyzed decomposition of ozone (Wojtowicz, 1998).
Taking together the above results of EPS removal shown in
Figure 6 with the inactivation rates in Figure 3a, the slow
inactivationrates in ozone water at 0.9 and 1.4 mg/L for
10 min may be explained by the lesser decrease of EPS in
the treatment with ozone at 1.0 mg/ L, and the more
effective removal of EPS at 2.0 mg/L could contribute to
the greater inactivation rate at the higher ozone concentration
of 3.2 mg/L. The amounts of EPS excreted into the
biofilms in the present experiment are too small to be
analyzed bychemical assay. Hence, for further studies on
the removal of EPS in the biofilms, this way of EPS observation
by CLSM will be helpful.

CONCLUSIONS

The cells in the biofilms of P. fluorescens and P. aeruginasa
were more resistant to ozone than their suspended
cells. However, the survival cells in both biofilms were
decreased to less than 1 % by exposure to ozone at ca. 1
mg/L for 5 minin the flow-through system. Each biofilm
established showed different inactivation rates in ozone
water at different ozone concentrations after various
exposure times. The decrease of inactivation rates with
increasing exposure time may suggest occurrence of diffusional
impediment a reactions of ozone with constituents
of the biofilms. These results indicate that, though
ozone is an...
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