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

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: 1.7x10(9) CFU/cm(2) and 7.5x10(2) CFU/cm(2) for aerobic species; 1.3x10(4) CFU/cm(2) and 2.1x10 CFU/cm(2) for anaerobic species; and 1.8x10(3) CFU/cm(2) and 4.6x10 CFU/cm(2) for sulfate-reducing species. However, the opposite trend was observed for the numbers of iron-reducing bacteria: 4.1x10(6) CFU/cm(2) at 12.85 g/l NaCl and 7.5 10(8) CFU/cm(2) 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.