Corrosion of Carbon Steel by a Thermophilic Sulfate-Reducing Consortium Enriched from Oilfield-Produced Waters

Corrosion of metal infrastructure due to microbial activity has been widely reported in many sectors and has been frequently studied under mesophilic conditions (<50°C). However, less is known about this degradation process at thermophilic (>50°C) temperatures that characterize many oil- and gas-producing operations. We used a thermophilic sulfate-reducing consortium (TSRM) enriched from offshore-produced water fluids to determine microbial corrosion of mild carbon steel at 60°C in the presence or absence of an organic electron donor (lactate or volatile fatty acids) and in the presence of riboflavin, a redox mediator previously reported to enhance microbial corrosion by pure isolates. Incubations of the TSRM consortium showed the highest corrosion rate in the absence of an organic electron donor, suggesting that the carbon steel itself served as an electron donor. Higher corrosion rates corresponded to increased numbers of localized pits formed. Scanning electron micrographs showed microbial cells with elongated filaments incubations when Fe0 served as an electron donor, potentially contributing to the direct uptake of electrons from iron. The addition of 20 ppm riboflavin did not enhance corrosion rates by the mixed TSRM consortium under the tested conditions. Microbial community analysis showed the TSRM culture to contain diverse anaerobic taxa and substantially distinct planktonic and coupon surface-attached communities. Overall, this study showed that thermophilic microbial communities containing sulfate-reducers can contribute to the corrosion of metal infrastructure operated or maintained at higher temperatures even in the absence of organic substrates, provided sulfate is present.