Effects of two main metabolites of sulphate-reducing bacteria on the corrosion of Q235 steels in 3.5 wt.% NaCl media

The electrochemical corrosion behaviour of Q235 steels in 3.5 wt.% NaCl solutions with sulphide and extracellular polymeric substances (EPS), the two main metabolites of sulphate-reducing bacteria, was separately investigated through potentiodynamic polarisation and electrochemical impedance spectroscopy. Either sulphide or EPS increased the anodic current density by nearly one order of magnitude and negatively shifted the corrosion potential. The effects of EPS at the initial stage of corrosion may be ascribed to the Fe2+-complexing capability and the quickly adsorbed film. Moreover, the feeble protective effect of EPS after 16 d of immersion was observed through scanning electron microscopy.

► Extracellular polymeric substances have been isolated from a batch culture of sulphate-reducing bacteria successfully.
► Sulphide and extracellular polymeric substances have triggered distinct electrochemical characteristics.
► ATR-IR analysis has confirmed the Fe2+-complexing capability of extracellular polymeric substances.
► In situ AFM results show extracellular polymeric substances can form a densely packed film on Q235 steels.
► The adsorbed extracellular polymeric substances film has protected the Q235 steels to a certain degree.