Biocorrosion Reduction of Pipeline Steel in Desulfovibrio ferrophilus Culture in the Presence of Carboxymethyl Chitosan Grafted Poly(2-methyl-1-vinylimidazole)/Cerium Molybdate Nanocomposite

Abstract

In oilfield water systems, the presence of sulfate reducing bacteria (SRB) has caused significant corrosion problems in recent times. On pipeline steel, SRB utilize extracellular electrons from iron oxidation for intracellular reduction of sulfate within the cytoplasm to produce energy, leading to microbiologically influenced corrosion (MIC). In this work, the effects of Desulfovibrio ferrophilus (strain IS5) SRB cellular growth on steel (X70 pipeline steel) corrosion within an anaerobic culture and oilfield-produced water are investigated. SRB are cultured in media of varying concentrations of organic carbon source, using lactate and citrate extracts. To combat MIC, we have also inoculated the SRB culture with different concentrations of a newly synthesized carboxymethyl chitosan grafted poly(2-methyl-1-vinylimidazole)/cerium molybdate nanocomposite. Without this nanocomposite, bacterial growth increased within the culture duration, leading to MIC. MIC episodes are observed as severe anodic steel dissolution. SRB cell counts reduced with the level of carbon source reduction after incubation, but significant cellular survival was observed at extreme carbon starvation. The rate of MIC reduced more than 90 times in the presence of this hybrid nanocomposite under anaerobic conditions, and this has been attributed to the inhibition of SRB cellular growth. D. ferrophilus biofilm growth on steel substrate was analyzed using confocal microscopy with appropriate fluorescent probes. From X-ray photoelectron spectroscopy evidence, the adhering biofilm/corrosion product aggregates on the metallic substrates were mostly ferrous oxides/sulphides. Extensive biocorrosion studies were conducted using electrochemical techniques. Linear polarization resistance and electrochemical impedance spectrometry data confirmed the trend in surface pitting patterns. Our experimental results demonstrate the efficacy of this new chitosan/poly(2-methyl-1-vinylimidazole)/cerium molybdate nanocomposite as a biocide. Without this nanocomposite, the energy needed for cellular survival was harnessed by a combination of extracellular iron oxidation and sulfate reduction even with insufficient carbon source within the media.