Review articleThe interaction of bacteria and metal surfaces
Introduction
Traditionally it has been assumed that the interaction of bacteria and metal surfaces always results in increased corrosion activity. The term microbiologically influenced corrosion (MIC) is usually interpreted as to indicate an increase in corrosion rates due to the presence of bacteria that accelerate the rates of the anodic and/or cathodic corrosion reaction, while leaving the corrosion mechanism more or less unchanged. The possibility of corrosion inhibition caused by microorganisms has rarely been considered. Videla [1] has presented a short summary of the literature concerning corrosion inhibition by bacteria. In this review different examples for the interaction of bacteria and metal surfaces will be presented that are based on work reported previously by various authors and work performed by the author with colleagues at other institutions and with his graduate students at CEEL.
Researchers at the University of Connecticut, University of Southern California and the University of California at Irvine have evaluated the concept of corrosion control using regenerative biofilms (CCURB) for a variety of materials such as Al 2024, mild steel and cartridge brass in laboratory tests [2], [3], [4], [5], [6], [7], [8] as well as field tests [9]. Recent results have shown that two strains of Shewanella produced corrosion inhibition of Al 2024, brass and mild steel in artificial seawater (AS) [10]. Al 2024 is very susceptible to pitting corrosion in seawater, however, it has been found that a number of microorganisms are able to prevent pitting of Al 2024 in AS. These results suggest that microbiologically induced corrosion inhibition (MICI) is a more common phenomenon than was previously assumed. It has been shown that MICI occurs only in the presence of a live biofilm. The concept of the bacterial battery has been evaluated recently and it has been found that the power output of this battery increased continuously for several weeks [11]. Finally, various types of microbial fuel cells (MFC) have been proposed in which bacteria are assumed to oxidize the fuel and transport electrons to the fuel cell anode [12].
Section snippets
Microbiologically influenced corrosion (MIC)
The interaction of bacteria and metal surfaces results in the formation of biofilms in a process known as biofouling. MIC has been reported in the chemical processing, oil and gas, and power generation industries in a wide variety of environments. Acid producing bacteria have been found to be the main cause of MIC of carbon steels. One of the first studies of MIC involved sulfate-reducing bacteria (SRB) that thrive only under anaerobic conditions and are found widespread in many waters and
Summary and conclusions
Corrosion inhibition caused by bacteria has been observed for Al 2024, mild steel and brass exposed to AS containing growth medium in the presence of S. algae or S. ana. Ecorr decreased in the presence of bacteria suggesting that the observed prevention of pitting for Al 2024 was due to the creation of anaerobic conditions on the metal surface as a result of which Ecorr is maintained at values that are lower than Epit which in abiotic AS is equal to Ecorr. The increase in the corrosion
Acknowledgements
The work on the bacterial battery and on the microbial fuel cell is being carried out by Esra Kus and Orianna Bretschger, respectively, who are Ph.D. students in the Mork Family Department of Chemical Engineering and Materials Science at USC.
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