Corrosion behavior and interaction of mixed bacteria on carbon steel in reclaimed water

At present, the researches on the corrosion of mixed microorganisms pay more attention to iron-oxidizing bacteria (IOB) and sulfate-reducing bacteria (SRB) in tap water or seawater. Pseudomonas fluorescens and Escherichia coli are two common microorganisms in reclaimed water, but there are few studies about their interaction on metal interface and about their influence on metal corrosion behavior. The corrosion behavior of carbon steel under mixed microorganisms of Escherichia coli and Pseudomonas fluorescens was studied by corrosion weight loss, electrochemistry, scanning electron microscopy (SEM) and X-ray diffraction (XRD) in this paper. The dominant bacteria under mixed bacteria conditions determined the final result of corrosion reaction in reclaimed water. On the first three days, the dominant strain was Escherichia coli, which produced acid on the surface of carbon steel and deteriorated corrosion. After the 3rd day, the dominant strain was Pseudomonas fluorescens, which inhibited the growth of Escherichia coli and slowed down corrosion. When the extracellular polymeric substances (EPS) concentration of Pseudomonas fluorescens reached 400 mg/L, it would inhibit the growth and reproduction of Escherichia coli. On the contrary, Escherichia coli EPS acted as a nutrient for Pseudomonas fluorescens, promoting the growth and reproduction of Pseudomonas fluorescens.