Microalgae Adherence on Stainless Steel: Its Effect on Corrosion

GÓMEZ DE SARAVIA SANDRA G.; RASTELLI SILVIA E.; VIERA MARISA

Simposio; 18th International Biodegradation and biodeterioration Symposium; 2021

International Biodeterioration & Biodegradation Society

Stainless steel (SS) materials have been widely used in different environments due to their good corrosion resistance. However, pitting corrosion induced by microorganisms is commonly observed. In this work, corrosion of 316L SS in the absence and presence of Scenedesmus vacuolatus (S. vacuolatus) was monitored using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. Coupons of SS were immersed vertically in a flask with S. vacuolatus culture in BG11 broth (initial OD (664nm)= 1.5) under constant agitation. The experiments were performed in duplicate. Coupons were withdrawn from the cultures after 7, 14 and 21 days. Sterile culture medium was used as control. Biofilm formation on the SS was analyzed using scanning electron microscopy (SEM) and metallographic microscopy and surface and corrosion products were analyzed using energy dispersive spectroscopy (EDS). SEM images showed a few grouped S. vacuolatus cells adhered to the SS coupon by extracellular polymeric substances (EPS) at the early times of exposure. At 21 daysof exposure, the number of attached alga cells increased and were homogeneously distributed over the surface. The OCP measurements made in the presence of algae presented strong oscillations, reflecting the effect of biofilm formation on the passive film. The OCP values measured in the sterile control showed a slight and steady increase during the 21 days. The diameters of Nyquist plots (ZIm vs Zreal) were lower in the presence of the biofilm and decreased gradually with time, reflecting that the attachment of S. vacuolatus enhanced SS corrosion.