Current approaches to identifying and monitoring microbially influenced corrosion (MIC) are limited by incomplete understanding of the mechanisms by which MIC might occur under a variety of environmental conditions and via a variety of microbial metabolisms. We have made zero-resistance ammetry (ZRA) measurements between shorted carbon steel coupons deployed as working electrodes (referred to as WE1 and WE2) in separate chambers connected by a semi-permeable membrane. Experimental manipulations (e.g. inoculation with microorganisms) were made to one chamber (WE1), and current between WE1 and WE2 was monitored. This split-chamber/ZRA approach allowed us to mimic the conditions associated with heterogeneous coverage of metal surfaces by microbial biofilms, while also assessing the associated microbiological metabolism. In experiments using the facultatively anaerobic bacterium Shewanella oneidensis MR-1, we observed bioreduction of the Fe(III) passive layer and current from WE1 to WE2, which induced depolarization of WE2. Mass loss measurments indicated that these activities resulted in protection of WE1 from corrosion, but enhanced corrosion of WE2. Similar experiments were carried out with S. oneidensis under nitrate-reducing conditions. Nitrite produced during nitrate reduction led to cathodic protection of WE1 and electron transfer from WE2 to WE1 and deterioration of WE2. Additionally, S. oneidensis appeared to use carbon steel Fe(0) as an electron donor for nitrate reduction when no other electron donor was available. Finally, the split-chamber/ZRA approach was used to evaluate MIC by fungi at a biodiesel-water interface using a “stacked electrode” approach, whereby WE1 was positioned in the water and WE2 was positioned in biodiesel. Metabolism of biodiesel components led to acidification of the water, while intrusion of fungal hyphae into the biodiesel layer allowed electrochemical connection between WE1 and WE2 and facilitated corrosion of WE1. Our results indicate that while a variety of mechanisms of MIC may occur, they can be detected using the split-chamber/ZRA approach, and we hope to develop an “index” of electrochemical signatures that may be used for sensitive MIC monitoring.

Evaluation of microbially-induced carbon steel corrosion using zero resistance ammetry in a split-chamber format

255th National Meeting (2018)

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