Bacterial biofilms on cathodically protected stainless steel

The influence of mixed anaerobic bacterial biofilms comprising Desulfovibrio vulgaris and Desulfovibrio desulfuricans and pure Vibrio alginolytics aerobic biofilms on cathodically protected AISI304L stainless steel (SS) coupons was studied by means of epifluorescence microscopy, scanning electron microscopy (SEM) and electrochemical measurements. SS samples were protected by applying -0.7 and -0.9 V vs saturated calomel electrode (SCE) potential levels during different exposure periods between 3 h and 14 d. Bacterial settlement and growth were reduced by cathodic protection in the initial stages of biofilm formation. The number of attached bacteria did not decrease when cathodic protection was applied on SS coupons after a stationary biofilm was formed. Localized attack by pitting was observed under both conditions (with and without protection) in the presence of the anaerobic bacteria. This could not be avoided by applying cathodic protection. Bacterial biofilms modified the morphology of calcareous deposits.