Corrosion control of mild steel by aerobic bacteria under continuous flow conditions

Corrosion of mild steel under aerobic conditions in the presence of a monoculture of aerobic bacteria (Pseudomonas fragi K [P. fragi K]) has been studied in a continuous flow system using electrochemical impedance spectroscopy (EIS). P. fragi K grown in Luria-Bertani (LB) medium causes a 10- to 20-fold decrease in the corrosion rate of mild steel after a biofilm becomes visible on the surface of the samples. Live viable bacteria are necessary for the observed corrosion reduction of mild steel, indicating an active role rather than a barrier effect of the biofilm. Flowing nitrogen through the solution was found to be less effective than P. fragi K in lowering the corrosion rate of mild steel, suggesting that an effect by bacteria, in addition to scavenging oxygen, is involved. The effect of nutrient flow rate on the ability of the bacteria to control corrosion was also examined. It was found that the corrosion inhibition of mild steel increases somewhat as the medium flow rate decreases below a certain level.