Studies on enhancement of biofilm formation and adherence due to mechanical treatment of titanium surfaces in cooling-water systems

Abstract

Titanium has proven to be the heat exchanger material of choice for seawater- cooled power plants owing to its outstanding resistance to pitting and crevice corrosion in a wide range of aggressive media. However, the inertness of the titanium surface makes it highly susceptible to biofilm formation and subsequent biofouling. This can hinder the heat transfer properties and flow of water. Fouling control strategies in condensers include a combination of mechanical, chemical and thermal treatments. However, reports from various industrial situations suggest that mechanical treatment may not have long-term effects. This study aimed to find out whether mechanical cleaning eventually enhances biofilm formation and increases the adherence of biofilm. In our studies epifluorescence micrographs of biofilms on control and mechanically treated titanium surfaces clearly showed accelerated biofilm formation as well as increased adherence on themechanically cleaned surface. Total counts of viable bacteria acquired by culturing technique, and biofilm thickness measurements made using microscopic techniques, confirmed this observation. Surface profilometry showed increased roughness of the titanium surface, facilitating adherence of biofilm. The number of microbial species was higher on mechanically cleaned and re-exposed surfaces than on fresh titanium. Thus we concluded that mechanical cleaning can increase biofilm formation and adherence of biofilm, thereby increasing the potential of biofouling in the long term.