The mutual co-regulation of extracellular polymeric substances and iron ions in biocorrosion of cast iron pipes

• A moderate concentration of iron ions (0.06 mg/L) promoted the production of EPS.
• EPS accelerated corrosion at the initial stage, but inhibited corrosion at the later stage.
• Functional groups in the EPS acted as electron shuttles to bind iron ions.
• The corrosion inhibition of EPS was correlated to phosphorus and corrosion products.

New insights into the biocorrosion process may be gained through understanding of the interaction between extracellular polymeric substances (EPS) and iron. Herein, the effect of iron ions on the formation of biofilms and production of EPS was investigated. Additionally, the impact of EPS on the corrosion of cast iron coupons was explored. The results showed that a moderate concentration of iron ions (0.06 mg/L) promoted both biofilm formation and EPS production. The presence of EPS accelerated corrosion during the initial stage, while inhibited corrosion at the later stage. The functional groups of EPS acted as electron shuttles to enable the binding of iron ions. Binding of iron ions with EPS led to anodic dissolution and promoted corrosion, while corrosion was later inhibited through oxygen reduction and availability of phosphorus from EPS. The presence of EPS also led to changes in crystalline phases of corrosion products.