The Electrochemical Detection Of Sulphate-reducing Bacteria And The Effect Of The Corrosion Behavior Of Carbon Steel D36 In Seawater

Sulphate-reducing Bacteria (SRB) existing in seawater, freshwater, earth, underground pipelines,petroleum and natural gas wells frequently contaminate environments, and in some case, cause corrosionof the metallic equipments and materials. Hydrogen sulphide, the production of SRB metabolism, is alsoquite toxic to nerve, and may cause permanent physical harm and even death to human. So it is necessaryto find a suitable method to detect the existence of SRB and the number of them timely using suitablemethod. Silver electrode method is one of the new techniques to detect the number of SRB, and it is notreported to use this method in seawater, so it is necessary for us to do some research. This silverelectrode method is easier, faster than traditional MPN technique, immunity methods and microscopemethods. In this paper, the relation between the growth of SRB in seawater environment and theelectrochemical state of the silver metal electrode has been studied. Results showed that theconcentration of sulphur ions, which was produced by the metabolism of SRB increased with theincrease of SRB number during the exponential growing time in discontinuous incubating environment.The results of polarization measurement confirmed that the increase of anode process was greater thanthe decrease of cathodic polarization affected by SRB. The addition of SRB caused the negative move ofcorrosion potential of silver electrode and the increase of corrosion velocity. The potential of silverelectrode responded to the sulphur ions produced by SRB sensitively. In seawater the potential of silverelectrode and the negative logarithm of the number of SRB were linear correlative. Therefore a sensor todetect SRB concentration was devised. And the effects of the response of the sensor were studied. Theresults of the sensor in practice were coincident with the results of MPN method. In conclusion, the silverelectrode method to detect the number of SRB in seawater environment was a better method, which wasextensive applicable, sensitive, precise and convenient. So the sensor of silver electrode to detect thenumber of SRB became an in-situ, fast, good method. Also the effects of SRB in the seawater state and the corrosion behavior of carbon steel D36 inseawater were studied. The results showed that the metabolism of SRB made sulphate changed intosulphide, and increased the redox potential and acidity, which led the corrosion potential of carbon steelD36 to a more negative value and increased its corrosion. The results of polarization measurement andelectrochemical impedance spectroscopy (EIS) confirmed that the mechanism of the corrosion in aboveprocedure was not changed, but the increase of anode process and part of cathode process were the maincause of corrosion. And it also could be confirmed that the SRB themselves and the intermediateproducts of metabolism didn't affect the corrosion of carbon steel D36 directly, and the increase ofcorrosion was caused by the S2- produced by the metabolism of SRB in the solution.