Corrosion of mild steel in an alternating oxic and anoxic biofilm system

The effect of alternating oxic and anoxic conditions (12 h oxic‐12 h anoxie) on sulfate reducing activity, iron‐sulfur chemistry and the corrosion of mild steel, has been studied in biofilm reactors. During the experiment (35 d) an increasing activity of sulfate reducing bacteria was observed. A part of the produced sulfide and iron sulfide (FeS) was oxidized during oxic periods and resulted in a mixture of acid volatile sulfides (mainly mackinawite, FeS), chromium reducible sulfur (mainly pyrite, FeS2) and elemental sulfur (S°). At the end of the experiment an amount of total S corresponding to 157 umol cm−3 was found within the deposit. Corrosion rates were measured electrochemically during the experiment and were found in the range of 3–5 mpy after 7 d to 120–160 mpy after 34 d. An extended aeration of the biofilm system for 1 month without addition of any organics showed that the pools of Fe‐S compounds in the deposit and the corrosion rate remained high. Microsensor studies of dissolved oxygen penetr...