https://biointerfaceresearch.com/ 5698 Article Volume 12, Issue 4, 2022, 5698 - 5708 https://doi.org/10.33263/BRIAC124.56985708 Effect of Bacillus megaterium Biofilm and its Metabolites at Various Concentration Biodiesel on the Corrosion of Carbon Steel Storage Tank Yustina M Pusparizkita 1,2* , Ardiyan Harimawan 1 , Hary Devianto 1 , Tjandra Setiadi 1,3 1 Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Bandung, Labtek X Jl. Ganesa, Bandung 40132, Indonesia; 2 Department of Environmental Engineering, Faculty of Engineering, Diponegoro University, Jl. Prof. Soedharto SH Tembalang, Semarang 50275, Indonesia; 3 Centre for Environmental Studies (PSLH), Institut Teknologi Bandung, Jl. Sangkuriang 42 A, Bandung 40135, Indonesia; * Correspondence: ympusparizkita@lecturer.undip.ac.id (Y.M.P.); Scopus Author ID 57201338677 Received: 19.08.2021; Revised: 30.09.2021; Accepted: 3.10.2021; Published: 21.10.2021 Abstract: Microorganisms in biodiesel storage tanks may generate bio-corrosion due to their hygroscopic and susceptible fuel degradation. The organisms, including Bacillus megaterium present in the hydrocarbons, resulted from the EPS and metabolites processes that subsequently control the corrosion process of the tank. This present study examined the effect of biodiesel concentration on microbial activity through TPC analyzing growth for B. megaterium. Furthermore, this study investigated EPS formation and acid metabolites production by B. megaterium based on SEM observations and acidimetric titration. Meanwhile, this study investigated the microorganism-induced corrosion impact based on gravimetric analysis. The results explained a higher biodiesel concentration in diesel oil promoted an increase in the growth of B. megaterium and the corrosion rate. Conversely, the acid metabolites produced from bacteria under the biofilm did not significantly increase the corrosion rate. Corrosion products resulting from the B. megaterium activity on the surface of the steel included Iron (II, III) oxide (Fe 2 O 3 and Fe 3 O 4 ). The formation of oxide and pitting may control the strength of the surface tank in the course of biofuel storage, which may lead to the failure of the material. Keywords: bio-corrosion; biofilm; Bacillus; biodiesel; metabolites. © 2021 by the authors. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). 1. Introduction Fossil fuel or biofuel is commonly stored in storage tanks in a given period. For this purpose, most hydrocarbon storage tanks are made of a material such as carbon steel because of their high strength and good formability. Nevertheless, carbon steel is susceptible to bio- corrosion under the influence of microorganisms present in hydrocarbon fuels. Particularly, biocorrosion processes at a metal surface favorably occur in aqueous environments of waste treatment facilities, including chemical and underground pipelines transporting oil and gas [1– 4]. In this case, biocorrosion of carbon steel storage, distribution, and infrastructure systems has significant economic impacts on maintenance costs and reduction of the fuel quality resulting from deterioration [5–8]. Further, biodiesel primarily comprises methyl esters of fatty acids (FAME) resulting from plant oils or animal fats' transesterification. This fuel is then blended with diesel fuel at varying concentrations. Biodiesel as a mixture with diesel fuel interacts with the metal surfaces