|Content Type||Conference Paper|
|Title||The Effect of Ozonated Cooling Water on the Corrosion Behavior of Stainless Steel, Titanium and Copper Alloys; Ozone Biocidal Action on Sessile and Planktonic Bacteria|
|Authors||Hector A. Videla and M.R. Viera, Universidad de La Plata; P.S. Guiamet and Monica F.L. de Mele, INIFTA|
|Source||CORROSION 99, April 25 - 30, 1999 , San Antonio, Tx|
|Copyright||1999. NACE International|
|Keywords||ozone, biofilm, Pseudomonas fuorescens, sessile bacteria, planktonic bacteria, cooling water, heat exchanger, l!|
Two aspects of ozone utilization as sole chemical treatment for cooling water demand a Ix3ter 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 expirements 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 and sessile bacteria, liquid cultures and biofilms of Pseudomonas florescens, formed on deferent 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 extra cellular 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.
Growing concerns of environmental impact and safety as well as regulatory pressure on the use of toxic biocides? have lead to look for environmentally safer biocides3>4or for environmentally acceptable water treatments. Taking into I account all these previous considerations, ozone has been proposed as a promising biocide for cooling water treatment6>7. The benefits of ozone treatment include8: a) minimal on site chemical inventory~, b) no toxicant discharge; c) potential of water conservation. However, the main cons of the use of ozone would be: a) incompatibility of ozone with other chemicals added to the water b) its aggressiveness against constructional materials of the system; c) incomplete documentation of its mechanism of action (as the sole treatment for cooling water) and d) the lack of general application guidelines. A considerable advance in the understanding on the use of ozone in cooling water systems has been gained since the beginning of the present decade through numerous discussions and publications made within the frame of NACE group committee T-7A-17 (use of ozone in cooling water systems) as well as in different sub-committees devoted to discussing ozone generation (17-a); case histories and performance data (17-b); ozone toxicity and safety considerations (17-c), etc. However, in spite of these efforts, two aspects that remain elusive and still demand a better understanding are: a) the effect of ozone on the corrosive behavior of structural materials in cooling water and b) a better knowledge about the effectiveness of ozone as a biocide for treating bacterial biofilms.
Among the few references available on item a), a general review of the effects of dissolved ozone on the corrosion behaviour of metals and alloys was published by Brown and Duquetteg. The authors point out that the great deal of conflicting data regarding the influence of ozone on the corrosion behavior of engineering alloys is mainly due to the use of coupon exposure tests in relatively uncontrolled environments such as actual cooling systems. The results of their report show that ozone has a large driving force for passive film formation on stainless steel, in artificial seawater.
|File Size||818 KB||10|