Pitting-corrosion of Metals by Indigenous Bacteria Isolated from Soils of Oil Producing Areas of Delta State in Nigeria

Abstract

Background: Microorganisms are able to affect various corrosion mechanisms, such as general corrosion and localized corrosion, including pitting and stress corrosion cracking. Corrosion of most metals is inevitable as presence of microbes is inevitable in the environment. The presence of microorganisms where those pipelines are buried allows the corrosion of these metallic pipelines. Aims: The study aimed to investigate metal corrosive potential of indigenous bacteria in the soil of oil producing areas of Delta State in Nigeria. Study Design: Bacteria isolated from soil samples collected along oil pipelines in oil producing communities of Delta State, identified using standard methods and screened for their potential to corrode metals were used for these analyses. Place and Duration of Study: Department of Environmental Management and Toxicology Federal University of Petroleum Resources Effurun, Delta state Nigeria. The study lasted for twelve months. Methodology: Biocorrosion potential was determined on the selected isolates by immersing sterile carbon steel coupons in sterile soil samples inoculated with the test organisms and weight loss and bacterial growth were determined monthly for a period of four months. Scanning Electron Microscopy (SEM EDX) was carried out to ascertain product composition and type of corrosion. Results: The isolates used in screening for corrosion capacity were Pseudomonas putida, P. aeruginosa, P. stutzeri, Shewanella putrefaciens, Desulfovibrio vulgaris and Vibrio vulnificus. The highest corrosion rate was 1.67 mpy and least was 1.21 mpy for Desulfovibrio vulgaris and V. vulnificus respectively. The scanned electron micrograph of metals showed that the isolates induced pitting corrosion while the control showed little or no pitting corrosion. Conclusion: This study ascertained that oil pipelines made of metals are prone to corrosion induced by bacteria in the soil. Thus, it is imperative to pay proper attention to microbially induced corrosion and to take appropriate measures to curb this menace to achieve desirable life spans of pipelines and other oil facilities and consequently reduce environmental pollution.