Use of dissolved ozone for controlling planktonic and sessile bacteria in industrial cooling systems

Cooling water treatment requires effective, environmentally-safe biocides c ompatible with system operation. The unique combination of high biocidal ac tivity during use with no toxic discharge, could render dissolved ozone a s afe biocide for cooling water treatment. Planktonic and sessile cells of Ps eudomonas fluorescens (a frequent microbial contaminant of industrial syste ms) were used in this work to assess the biocidal effectiveness of ozone. D issolved ozone showed to be effective at concentrations between 0.1 and 0.3 ppm, to eliminate completely the levels of planktonic cells used in this p aper (10(7)-10(8) cell/ml) within a range of contact times between 10 and 3 0 min. However, ozone at 0.15 ppm was only able to diminish sessile cell po pulation by two or three orders of magnitude. This minor biocidal effective ness of ozone against bacterial biofilms is discussed in this paper, taking into account recent concepts on structure and dynamics of biofilms. Differ ent metallic substrata were assayed to verify if there was any effect of me tal nature on the biocidal action. Open circuit potentials vs, time experim ents and potentiodynamic polarization curves were made for assessing the ef fect of dissolved ozone on the corrosion behavior of the metals tested. (C) 2000 Elsevier Science Ltd. All rights reserved.