DIVERSITY OF MICROBIAL INDUCED CORROSION ON CARBON STEEL ST 37 AT CIRATA RESERVOIR

• Main Author: Nabila El Faidah, Farah
• Format: Theses
• Language: Indonesia
• Subjects: Ilmu hayati ; Biologi
• Online Access: https://digilib.itb.ac.id/gdl/view/32720
• Institution: Institut Teknologi Bandung

Corrosion can reduce the strength of the metal and cause a malfunction in the process unit, economically this will be very detrimental. Corrosion can be caused by physical, chemical or biological factors or from the role of microbes. The most known microbes that play a role in the corrosion process are sulfate reducing bacteria. Cirata Reservoir is a reservoir that has a hydropowerplant that use metal in its system units. Nowdays, the water quality of Cirata reservoir has declined, one of which is caused by the increasing number of floating net cages. This study aims to determine the effect of microbes in the biocorrosion process in the Cirata reservoir, and to determine the corrosion rate on carbon steel directly on a laboratory scale caused by microbes using Cirata reservoir water as inoculum. ST 37 carbon steel was immersed in the Cirata reservoir at a depth of 0.3 meters and 2 meters from the surface, and was sampled after 120 days and 240 days of immersion. The physical-chemical parameters of water that measured were pH, temperature, DO, conductivity, nitrate, nitrite and sulfate concentrations. The 150 ml water sample was filtered using a 0.22 ?m polycarbonate membrane. Bacterial functional genes were analyzed using qPCR, with the 16S rRNA gene used to calculate the total bacterial abundance and dsrA genes to calculate the abundance of sulfate reducing bacteria. Identification of bacterial diversity was carried out using Illumina Miseq. Corrosion products were observed by SEM-EDS and FTIR. In laboratory-scale experiments, carbon steel coupons were immersed in vial bottles containing reservoir water as a medium and inoculum concentrate. Then carried out observations, biofilm formation on steel and corrosion rate every 14 days. Temperature, pH and DO at 0.3 meters (32.6oC; 7.1 and 6.53 mg/l) were higher than 2 meters, but the conductivity tended to not differ (230-232 S/m). The concentration of nitrates, nitrites and sulfates is relatively not different at both depths. The total abundance of planktonic bacteria in the Cirata reservoir is around 105 - 106 copies/ml and the abundance of biofilm bacteria is around 103 copies/cm2 for 240 days of immersion. The abundance of sulfate reducing bacteria is very low in planktonic and biofilm bacteria which is below 10 copies/ml. The most dominant bacteria in planktonics and biofilms are Flavobacterium, Mycobacterium and Fluviicola. Several other dominant bacteria are widely known to be biofilm forming bacteria. In the biofilm it was identified a group of sulfate reducing bacteria, Desulfovibrio, and a group of iron oxidizing bacteria, Sediminibacterium. The corrosion rate of carbon steel after the 240 days was 0.4 mm/year. From SEM visualization was known several bacterial cells attached to the steel surface, and known a shape of hexagonal or globular corrosion products. FTIR spectra showed the presence of amide bonds, hydroxyl acid and CH bonds in corrosion products. In laboratory-scale experiments, sulfate content decreased in observations from 2 weeks to 4 weeks, cell density reached 107 CFU/ ml, and showed a positive presence of sulfate reducing bacteria. The corrosion rate in steel metals on a laboratory scale is 0.12 mm/year.