Corrosion mechanisms of Escherichia coli and Pseudomonas fluorescens on carbon steel based on biofilm perspective

Corrosion mechanisms of Escherichia coli, Pseudomonas fluorescens and E. coli–P. fluorescens on carbon steel were researched by the corrosion weight loss, electrochemical impedance, microbial inoculation culture, biofilm three-dimensional layer scanning, environmental scanning electron microscope, infrared spectroscopy and other methods. It was found that the corrosion rate in E. coli condition was 1.37–1.48 times higher than that in P. fluorescens condition and 1.23–1.33 times higher than that in E. coli–P. fluorescens condition. Although the types of functional groups contained in the EPS secreted by E. coli and P. fluorescens were the same, the hydrogen bonding was weaker in the former, resulting in a loose biofilm structure. Meanwhile, the metabolic corrosion of E. coli itself dominated in the corrosion. On the contrary, P. fluorescens condition and E. coli–P. fluorescens condition had stronger hydrogen bonding of functional groups, so their biofilm structure was tighter. For P. fluorescens condition, the corrosion behaviour was dominated by inhibitory action of EPS in late. For E. coli–P. fluorescens condition, the corrosion behaviour was dominated by metabolic corrosion of E. coli–P. fluorescens itself in early. However, corrosion behaviour was dominated by inhibitory corrosion of EPS in middle. E. coli–P. fluorescens itself and EPS had comparable roles in late.