The effect of sulphate reducing bacteria on corrosion and cathodic protection of a steel has been studied in silt obtained from the bottom of Sumida River and in an inoculated midium consisted of peptone, yeast extract, MgSO4, Na2SO4, NaCI, lactic acid and water. Sulphate reducing bacteria accelerates corrosion by depolarizing cathodic reaction. The film formed on the steel surface through reaction with hydrogen sulphide, a metabolic product of the bacteria, is essentially protective but it tends to break down locally to form galvanic cells which accelerate corrosion. The critical potential for complete cathodic protection of the steel is -0.9 V (SCE) which is approximately 0.1 V more negative than the ordinary protection potential in the absence of the bacteria.

No abstract