Scale Formation by Calcium-Precipitating Bacteria in Cooling Water System

Scale formation in heat exchanger tube reduces heat transfer efficiency and enhances corrosion. Scale formation in cooling water is due to many factors including pH, temperature, salt etc. In this study, microbiological aspects of scale formation and their role on corrosion are presented. The calcium precipitating bacteria (CPB) were isolated from the scales collected from heat exchanger tube in a gas turbine power station using B4 medium. The dominant CPB was isolated and identified using 16s rRNA sequencing, and the phylogenetic analysis reveals that the predominant bacteria were Serratia sp. (FJ973548), Enterobacter sp. (FJ973549, FJ973550), and Enterococcus sp. (FJ973551). The nature of crystal deposits of bacteria has been explained. The corrosion behavior of CPB on mild steel was studied by the electrochemical method (polarization and impedance), and the biogenic calcium scale formations in CPB were analyzed by XRD method. The scale formation by bacteria reduced the cathodic corrosion current, where resistance was lower in the presence of bacteria. It is claimed that the CPB is one of the causative factor for scale formation and corrosion in cooling water system.