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ABSTRAK Yuvita Elvarina Fatimah
PUBLIC Alice Diniarti

The water cooling system is one of the most important units in the industry. This is because in the cooling system, a heat exchange process occurs to lower water temperature caused by overheating which can result in decreased effectiveness and damaged machinery in manufacturing. However, temperature alteration and organic matter in water cooling systems can support the growth of microbes such as biofilm-forming microbes. The biofilm formed in the cooling water system can accelerate biocorrosion, therefore a compound that can inhibit and eradicate the forming of biofilms is needed. Biosurfactant is one of the potential compounds that can be used to eradicate biofilms because it has anti-adhesion, and anti-biofilm activity, is easily degradable, non-toxic, and can be used over a wide range of conditions. Therefore, this study aims to determine the activity of biosurfactant F7 as an anti-adhesion and anti-biofilm on gram-positive and gram-negative bacterial biofilms by determining the MBIC and MBEC values and their effect on the corrosion rate of Carbon Steel ST 37. This research was conducted by constructing a biofilm formation curve from single cultures of isolates 1 (gram-positive bacteria) and 5 (gram-negative bacteria) on Carbon Steel ST 37 with general medium Nutrient Broth. In addition, the activity of biosurfactant F7 as an anti-biofilm was determined by determining the value of MBIC and MBEC on biofilm isolates 1 and 5. The MBIC and MBEC values were determined by measuring the wet weight of the biofilm formed. Meanwhile, the steel corrosion rate was carried out by measuring of the decrease in steel mass. The results of this study indicate that the maturation time of biofilm is 6 days for gram-positive bacteria and 3 days for gramnegative bacteria. In addition, the MBIC and MBEC values of biosurfactant F7 were 28.5 ppm and 570 ppm. After being given biosurfactant treatment with 28.5 ppm concentration, the corrosion rate of Carbon Steel ST 37 which was incubated by isolates 1 and 5 showed a decrease of 0.02321 mm/year and 0.01547 mm/year if compared to the untreated control. Meanwhile, the addition of the biocide glutaraldehyde as much as 0.5% (v/v) caused the corrosion rate of 0.02063 mm/year and 0.00773 mm/year. Therefore, based on this study, it can be concluded that F7 biosurfactant is more effective in inhibiting biocorrosion on Carbon Steel ST 37 when compared to glutaraldehyde.