Biofilm formation and its induced biocorrosion of metals in seawater

Abstract

This research examines several issues related to biofilm formation, and the biocorrosion of metals. A novel sulphate-reducing bacterium (SRB), designated Desulfovibrio singaporenus strain SJI1, was isolated from seawater near St. John Island, Singapore. The bacterium oxidizes lactate to acetate via pyruvate as the intermediate during sulphate reduction. Acetate is further partially oxidized to CO 2 when it is used as an electron donor. The adhesion of two anaerobic sulphate-reducing bacteria (D. desulfuricans and D. singaporenus ) and an aerobe (Pseudomonas sp.) to four polished metal surfaces was examined using atomic force microscopy (AFM) with cell probes. The cell-cell interactions show that there are strong electrostatic repulsion forces between bacterial cells. Biocorrosion behavior of SS316 by the two SRBs was investigated by analyzing the biofilm and pit morphology using AFM. Electrochemical impedance spectroscopy (EIS) results were interpreted with an equivalent circuit to model the physicoelectric characteristics of the electrode/biofilm/solution interface. A layer-by-layer coating on SS316 substrate alternately with quaternized polyethylenimine (q-PEI) and poly(acrylic)acid (PAA) to form polyelectrolyte multilayers (PEM) was investigated. The multi-layers stability test and anti-biocorrosion tests indicate that PEM have potential applications in the inhibition of biocorrosion of metal substrates. Corrosion inhibition of mild steel and SS316 by an organic inhibitor 2-Methylbenzimidazole (MBI) in seawater was also investigated. MBI predominantly controls the cathodic reaction. The corrosion inhibition effect of MBI on MIC is partially due to the inhibition of the bacterial activity.