Evaluation of biofilms formation and corrosion of steel by microscopic techniques and electrochemical impedance spectroscopy

Abstract

A clean metal surface which contacts natural or industrial waters undergoes a series of processes that lead to the formation of inorganic deposits and biofilms. In these structures, microorganisms adhere irreversibly to the substrate, embedded in a matrix of extracellular polymeric substances (EPS). The problems arising from biofilm formation, such as microbiologically influenced corrosion (MIC), loss of equipment performance, product damages, generate economic costs and may lead to structural failures with consequences for operators and/or users. The aim of this study was to evaluate the corrosion associated with the formation of bacterial biofilms on carbon steel surfaces. Bacterial cultures used in the experiments were isolated from different systems that presented MIC. SAE 1010 carbon steel coupons were placed in cultures for biofilm development. After 48 h coupons were extracted and bacterial adherence was measured by viable bacteria counts, epifluorescence microscopy, crystal violet assay and EPS quantification. The biofilm morphology was analyzed by scanning electron microscopy (SEM) and epifuorescence microscopy. Surface deterioration was monitored using electrochemical impedance spectroscopy and open circuit potential measurements. Studies carried out allowed correlating the adherence of the tested strains with the degree of attack suffered by the SAE 1010 carbon steel coupons.