Copyright © 2018 Aida Nur Ramadhani et. al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (4) (2018) 2009-2012 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET doi: 10.14419/ijet.v7i4.15592 Research paper Water content effect on biofilm formation and bio-corrosion process in biodiesel-diesel storage tank Aida Nur Ramadhani 1 *, Ardiyan Harimawan 1 , Hary Devianto 1 1 Chemical Engineering Department, Faculty of Industrial Technology, Institut Teknologi Bandung Bandung 40132 Indonesia *Corresponding author E-mail: Abstract This study focused in the effect of water content on biofilm and bio-corrosion, and knowing its influence on biodiesel-diesel blends’ quality. Biodiesel is hygroscopic and less stable, makes this fuel needs more attention in storing. Fuel is usually stored in a storage tank of carbon steel which easily corroded by microorganisms, such as Bacillus megaterium. Corrosion occurs because microorganisms use fuel as nutri- ents and water content in hygroscopic biodiesel supports to grow and metabolize. Experiments were carried out by immersing carbon steel in medium 30% biodiesel (B30) for 21 days with water content variation of 0%, 5%, and 10% volume. The number of colonies in biofilms increased up to 1,3 times in a 10% water content. A uniform biofilm provides an inhibitory effect on corrosion per time, also layer of iron phosphate formed on water content variation, so the highest 0.642 ± 0.28 mm/year on 0% water content. Fe2O3, Fe3O4, and FeOOH are the corrosion product by Bacillus megaterium. The highest biodegradation efficiency achieved by variation water content both 5% and 10% were 68.5% and 67.23%, and then followed by no water content at 60.40%. Keywords: Bacillus Magisterium; Bio Corrosion; Biodiesel; Biofilm; Degradation; Water Content. 1. Introduction World energy demand, especially for petroleum oil as a fuel, has increased significantly every year. Petroleum fuel (BBM) domi- nates national energy demand by 31.2% by 2015, and will increase to 40.7% by 2050 (BPPT, 2016). In 2016, Indonesia needs 14 mil- lion kiloliters of fuel oil (BPH Migas, 2016). Therefore, innovation and development of alternative energy is needed. One of the potential alternative fuels in Indonesia is biodiesel. Bio- diesel can be produced from natural raw materials, such as palm oil. Palm oil itself is the largest commodity in Indonesia, which is 31,284.30-kilo tons production in 2015 (BPS, 2017). In its applica- tion as a fuel, biodiesel can be mixed with petroleum diesel or often referred to as diesel. The use of biodiesel as a fuel mixture has been regulated by the government in ESDM Ministerial Regulation No.12 of 2015, which in 2025 will use 30% of biodiesel. Different biodiesel properties with diesel fuel make more attention to main- taining fuel quality. Biodiesel has high cetane number, biodegradable, and low emis- sions, but more unstable than diesel (Fazal et al.,2010; Haseeb et al., 2010; Jakeria et al.,2014; Lohani, et.al. 2014, Akpor, et. al. 2014; Adebayo and Oluwadare, 2014 ). The content of unsaturated fatty acids makes biodiesel susceptible to oxidation (Monyem and Gerpen, 2001). In addition, the hygroscopic nature of biodiesel causes high water content dissolved in biodiesel (Fregolente et al., 2012; He et al., 2007). This dissolved water content in certain con- ditions will precipitate to the bottom of the tank. This process will repeat continuously until it forms a layer of free water at the bottom of the tank. The presence of this free water layer can trigger the formation of sludge that can obstruct the system (He et al., 2007). On the other hand, water may increase the growth of microorgan- isms that can trigger corrosion (Groysman, 2014). Frequently used fuel storage method is the ground storage tank. Storage tanks are generally made of carbon steel. Carbon steel is easily fabricated, protect biodiesel from exposure to sunlight, and its price is cheaper than stainless steel (Groysman, 2014; Komariah et al, 2017; Restrepo-Florez et al, 2014). However, carbon steel has a weakness that is easily corroded, either chemically or by micro- organisms because stainless steel has more protective action of chromium and nickel elements (Heyer et al., 2013; Adebayo et al., 2014; Kovács et al., 2015). Corrosion is an interaction reaction between the metal and its envi- ronment, occurs because of the tendency of the metal to return to its original condition, the oxidant state in nature (Zarasvand and Rai, 2014; Beech and Sunner, 2004). Corrosion contributes to the de- struction of industrial piping and storage systems. Approximately 20% of petroleum product leakage is caused by corrosion in the tank (Groysman, 2014). Corrosion processes that occur include chemical and biological corrosion. Biologically, corrosion is caused by the activity of microorganisms that play a role in corrosion mechanism. One of the role of microorganisms in corrosion is by the formation of biofilms on the metal surface. Biofilm is one of the survival strategies of microorganisms. Micro- organisms use fuel as a carbon source and water to grow and me- tabolize. Carbon steel is one type of metal that is easily corroded because of its tendency to form an oxide layer which is the ideal place for the attachment of microorganisms (Heyer et al., 2013). The existence of this biofilm causes a non-uniform oxygen concen- tration on the metal surface (Lewandowski and Beyenal, 2008). Biofilm-enclosed areas will be oxygen deprived and an anaerobic anodic condition, and vice versa to cathodic conditions. This results is a potential difference from anodic to cathodic, and then corrosion occurs. One of the microorganisms that have been studied survive on hy- drocarbon medium is Bacillus megaterium. B. megaterium is found in pipelines and hydrocarbon storage systems, causing corrosion