Microbial-Influenced Corrosion of Corten Steel Compared with Carbon Steel and Stainless Steel in Oily Wastewater by Pseudomonas aeruginosa HAMIDREZA MANSOURI, 1,3 SEYED ABOLHASAN ALAVI, 1 and MEYSAM FOTOVAT 2 1.—Department of Chemical Engineering, Science and Research Branch of Tehran, Islamic Azad University, Tehran, Iran. 2.—Development & Engineering Management Department, South Pars Gas Complex Company, Assaluyeh, Iran. 3.—e-mail: hamidreza2010@gmail.com The microbial corrosion behavior of three important steels (carbon steel, stainless steel, and Corten steel) was investigated in semi petroleum medium. This work was done in modified nutrient broth (2 g nutrient broth in 1 L oily wastewater) in the presence of Pseudomonas aeruginosa and mixed culture (as a biotic media) and an abiotic medium for 2 weeks. The behavior of cor- rosion was analyzed by spectrophotometric and electrochemical methods and at the end was confirmed by scanning electron microscopy. The results show that the degree of corrosion of Corten steel in mixed culture, unlike carbon steel and stainless steel, is less than P. aeruginosa inoculated medium because some bacteria affect Corten steel less than other steels. According to the experiments, carbon steel had less resistance than Corten steel and stainless steel. Furthermore, biofilm inhibits separated particles of those steels to spread to the medium; in other words, particles get trapped between biofilm and steel. INTRODUCTION Microbial adhesion to surfaces and biofilm for- mation occur in natural environments and indus- trial processes. 1,2 Biofilms are cells that are attached to a surface by extracellular polymeric substances (EPS). This bacterial aggregation is a phenomenon that resists from the separation of microorganisms and makes some multicellular clusters. 3 Figure 1 shows the model of biofilm for- mation and cell aggregation by EPS on the surface. The strong adhesive EPS is composed of polysac- charides, lipids, and proteins (enzymes). It helps the microorganisms adhere to the surface of the steel irreversibly. 4,5 The heterogeneous biofilm and associated bacte- ria form complex biological systems that can cause several chemical changes at the metal/biofilm in- terface, such as gradients in pH and dissolved oxy- gen, chloride, and sulfate. 2,6,7 Under aerobic conditions, the microbial coloniza- tion usually leads to the formation of differential aeration and cellular concentration due to the metabolism of the bacterial colony. The production of the cellular concentration has some adverse ef- fects on passive film and facilitates the initiation of cracking corrosion. 8 Microorganisms change the corrosion process by altering the electrochemical conditions at the met- al/solution interface. These changes can have dif- ferent effects on microbiologically influenced corrosion inhibition (MICI) against microbiological- ly influenced corrosion (MIC). 8 All microbiologically influenced corrosions behave based on the three following characteristics: 9 (I) they are electrochemical processes; (II) microor- ganisms affect their extent, severity, and course; and (III) for them to initiate, microorganisms, nu- trients, and water must be present. Although most of oily wastewater will be separated from gas in refineries, a little of this wa- ter precipitates microbial growth and biocorrosion at the bottom of vessels. Previously scientists had experimented MIC in artificial media that could not reflect real industrial conditions. 10–13 JOM DOI: 10.1007/s11837-015-1429-1 Ó 2015 The Minerals, Metals & Materials Society