The Electro-active Characteristics Of Sulfate-reducing Bacteria And Its Influence On The Anaerobic Corrosion Of Carbon Steels

Sulfate-reducing bacteria (SRB) as a heterogeneous group of anaerobic heterotrophic bacteria were the main bacteria responsible for the numerous biocorrosion cases. Severe attention has been paid on the mechanism of the biocorrosion caused by SRB as abundant metal constructions have been used in marine environments. The electroactive characteristics of the SRB biofilm in anaerobic conditions were studied in this paper. The electron transfer process between SRB biofilm and solid electrode was also studied, and then the effect of carbon steel on the metabolism of SRB was further studied. The electron transfer between the electroactive SRB biofilm and carbon steel was studied by electrochemical methods and the biocorrosion mechanisms were analyzed.The electro-active characteristic of SRB biofilm on the pyrolytic graphite electrode (PGE) was firstly studied. The cyclic voltammetry curves of PGE with SRB biofilm showed two corresponding redox peaks which were related to the hydrogen evolution and oxidation. The overpotential for the reactions decreased in the presence of SRB biofilm. When the PGE with biofilm was polarized at 0.24 V, an oxidation current related to the hydrogen oxidation was found. The SRB biofilm also could obtain electron from-0.61 V polarized PGE to form hydrogen. The electron transfer resistance also decreased as the formation of SRB biofilm by the non-destructive electrochemical impendence spectroscopy detection. The hydrogen evolution and oxidation was an important approach for the electron transfer between SRB biofilm and solid electrode in anaerobic environment.The SRB biofilm could obtain electrons from the negative polarized PGE, and the polarized potential was similar to the corrosion potential of carbon steel. Therefore, the influence of carbon steel on the metabolism of SRB was further researched. The number of the SRB cells with carbon steels was larger than that without carbon steels. The metabolism of carbon source and sulfate was accelerated in the presence of carbon steels. Importantly, the amount of sulfate reduced was higher with carbon steels. The carbon steel was a potential electron donor for SRB to reduce sulfate.The influence of the electro-active SRB biofilm on the corrosion characters of the carbon steels was finally studied. The corrosion potential and the corrosion rate increased as the growth of the SRB. The metabolism alone could not accelerate the corrosion rate for long time. The effect of the metabolism was mainly caused by the sulphide. SRB biofilm could directly obtain electrons from-0.75 V polarized carbon electrode to catalyze the evolution of hydrogen. The electro-active SRB biofilm could obtain electrons directly from carbon steels, which induced the positive shift of the corrosion potential and acceleration of the corrosion rate.