Two aspects of ozone utilization as sole chemical treatment for cooling water demand a better understanding: a) the effect of dissolved ozone on the corrosion behavior of heat exchanger structural materials and b) the biocidal action of ozone on bacterial biofilms. To assess the effect of ozone dissolved in synthetic cooling water on the corrosion behavior of different structural materials (stainless steel; 70:30 copper-nickel; aluminum brass and titanium), voltamperometric experiments and
corrosion potential vs. time measurements were made at ozone concentrations between 0.1 and 1.2 ppm. Present results show that the passive behavior of stainless steel and titanium is not affected by dissolved ozone whereas copper alloys are susceptible to corrosion in the presence of ozone. To study the biocidal action of various concentrations of dissolved ozone against planktonic sessile bacteria, liquid cultures and biofilms of Pseudomonas flourescens, formed on diilerent structural materials, were used at different contact times. Our results show that dissolved ozone is an effective biocide for controlling planktonic cells but its effectiveness decreases in the presence of sessile bacteria and the extracellular polymeric matrix of the biofilm. It is
suggested that the penetration of ozone through the biofilm depends on the simultaneous diffusion and reaction of the biocide with the biofilm matrix which may exhibit local differences in biomass distribution and hydrodynamic conditions. Keywords: ozone, biofilm, Pseudomonasfuorescens, sessile bacteria, planktonic bacteria, cooling water, heat exchanger, stainless steel, copper alloys, titanium.