The acceleration of localized copper corrosion by extracellular polymeric substances of sulfate-reducing bacteria

Microbial-induced corrosion (MIC) of copper pipelines, especially in sulfate-reducing bacteria (SRB)-rich environments, poses a significant challenge. Despite its importance, the role of SRB-secreted extracellular polymeric substances (EPS) in copper corrosion particularly their time-dependent interactions remains unclear. This knowledge gap limits the development of effective corrosion mitigation strategies. In this study, we investigate the impact of EPS on copper corrosion using electrochemical and surface characterization techniques. Our findings reveal that EPS exhibits a dual role in copper corrosion. During the initial immersion phase (1-3 days), EPS adsorption forms a protective layer, temporarily inhibiting corrosion. In the middle stage (4-8 days), EPS accelerates corrosion by degrading the copper oxide film, as evidenced by a negative shift in the breakdown potential (E_b). In the final stage (9-14 days), uneven EPS coverage exacerbates localized corrosion. Thus, SRB-secreted EPS initially acts as a corrosion inhibitor but later promotes localized corrosion through oxide film disruption and non-uniform coverage. We systematically investigated the mechanisms of EPS-mediated corrosion inhibition across different immersion periods, identifying the critical transition threshold between the inhibition and promotion phases.