Effect of different salinities of a dynamic water system on biofilm formation

Abstract

AISI-1020 carbon steel coupons were fixed onto a water circulation loop in order to study the effect of varying NaCl concentrations on formation of biofilms by natural populations of microorganisms. Overall, we observed a reduction in the number of bacteria attached to the metal surfaces as NaCl levels increased. At 12.85 and 80 g/l NaCl, the respective bacterial counts were: 1.7×109 CFU/cm2 and 7.5×102 CFU/cm2 for aerobic species; 1.3×104 CFU/cm2 and 2.1×10 CFU/cm2 for anaerobic species; and 1.8×103 CFU/cm2 and 4.6×10 CFU/cm2 for sulfate-reducing species. However, the opposite trend was observed for the numbers of iron-reducing bacteria: 4.1×106 CFU/cm2 at 12.85 g/l NaCl and 7.5 108 CFU/cm2 at 80 g/l NaCl, respectively. Fungal counts remained constant throughout the experimental period. The salt concentration at which the maximum corrosion rate was observed was 35 g/l. In view of the marked loss of metal mass recorded at this salinity, AISI-1020 carbon steel proved to belong to the group of alloys less resistant to corrosion. Journal of Industrial Microbiology & Biotechnology (2000) 25, 45–48.