Abstract
Currently, sulfate-reducing bacteria (SRB) is regarded as the main culprit of microbiologically influenced corrosion (MIC), mainly due to the low reported corrosion rates of other microorganisms. For example, the highest reported corrosion rate for methanogens is 0.065 mm/yr. However, by investigating methanogen-induced microbiologically influenced corrosion (Mi-MIC) using an in-house developed versatile multiport flow test column, extremely high corrosion rates were observed. We analyzed a large set of carbon steel beads, which were sectionally embedded into the test columns as substrates for iron-utilizing methanogen Methanobacterium IM1. After 14 days of operation using glass beads as fillers for section separation, the highest average corrosion rate of Methanobacterium IM1 was 0.2 mm/yr, which doubled that of Desulfovibrio ferrophilus IS5 and Desulfovibrio alaskensis 16109 investigated at the same conditions. At the most corroded region, nearly 80% of the beads lost 1% of their initial weight (fast-corrosion), resulting in an average corrosion rate of 0.2 mm/yr for Methanobacterium IM1-treated columns. When sand was used as filler material to mimic sediment conditions, average corrosion rates for Methanobacterium IM1 increased to 0.3 mm/yr (maximum 0.52 mm/yr) with over 83% of the beads having corrosion rates above 0.3 mm/yr. Scanning electron images of metal coupons extracted from the column showed methanogenic cells were clustered close to the metal surface. Methanobacterium IM1 is a hydrogenotrophic methanogen with higher affinity to metal than H2. Unlike SRB, Methanobacterium IM1 is not restricted to the availability of sulfate concentration in the environment. Thus, the use of the multiport flow column provided a new insight on the corrosion potential of methanogens, particularly in dynamic conditions, that offers new opportunities for monitoring and development of mitigation strategies. Overall, this study shows (1) under certain conditions methanogenic archaea can cause higher corrosion than SRB, (2) specific quantifications, i.e., maximum, average, and minimum corrosion rates can be determined, and (3) that spatial statistical evaluations of MIC can be carried out.
Highlights
Steel is the most used metal on Earth due to its material properties, such as high strength and formability, as well as low production costs (Enning and Garrelfs, 2014)
Methanobacterium-affiliated IM1 (Dinh et al, 2004) isolate was obtained from Dr Friedrich Widdel (Max Planck Institute for Marine Microbiology, Germany), Desulfovibrio ferrophilus IS5 and Desulfovibrio alaskensis 16109 were purchased from DSMZ culture collection (DSMZ, Germany)
In the stationary batch culture experiments, the highest corrosion rate was observed for D. ferrophilus IS5, which was 0.35 ± 0.11 mm/yr, 3.6-fold higher than the flow system corrosion rate (Table 1)
Summary
Steel is the most used metal on Earth due to its material properties, such as high strength and formability, as well as low production costs (Enning and Garrelfs, 2014). Indirect corrosion through the production of corrosive metabolites or through electron mediators (Al Abbas et al, 2013; Pinnock et al, 2018; Jia et al, 2019), and direct uptake of electrons from the metal surface using cytochrome or pili, hereby leading to metal dissolution are well-identified for sulfate-reducing bacteria (SRB) (Kakooei et al, 2012; Enning and Garrelfs, 2014; Pinnock et al, 2018; Jia et al, 2019). Reduction of sulfate by SRB using either organic acids (Eq 1) or iron (Eq 2) as electron donor results in the production of sulfide or sulfite that forms a corrosive cell (cathode) on the metal surface (anode) (Enning and Garrelfs, 2014; Rémazeilles et al, 2017)
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