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Strategies Analysis of Microbiological Influenced Corrosion by Thermophilic Bacteria
microbiological influenced corrosion
環保工程, 生物技術, 材料科技
AbstractIn the presence, molybdate is added as corrosion inhibitor to the cooling water syatem of one power plant. However, it is shown that the growth of microorganisms induced microbiologically influenced corrosion (MIC) in the water pipelines of cooling water system. Thirteen strains of mesophiles and ten strains of thermophiles have been isolated from the slime of this system. Antimicrobial agents which can inhibit the growth of isolated mesophiles have been found, but effective antimicrobial agents for the isolated thermophiles need to be investigated. The main purpose of this research is to inhibit the incidence of biofilm growth, in order to solve the problem of biological corrosion of the cooling water system. The corrosion characteristics are evaluated by potentiodynamic polarization test, AC-impedance tests, corrosion potential trends, and scanning electron microscope observation. The long-term inhibitory effects of antimicrobial agent alone as well as in the presence of corrosion inhibitor to each strain of thermophilic bacteria are examined, in order to find appropriate antimicrobial agent and to determine the optimal dosage of corrosion inhibitor. The results indicated that ten strains of thermophiles could be inhibited by more than 50 ppm antimicrobial agent A within 1600 hours whether molybdate is present or not. MIC was simulated by inoculation of the isolated strain, TPH-2, TPH-5-2, TPH-13-3, with or without antimicrobial agent to see the inhibitory effect of corrosion on carbon steel by antimicrobial agents. The growth of isolated strains could be inhibited by antimicrobial agent T, antimicrobial agent N and antimicrobial agent A, but the corrosion of carbon steel was not inhibited. In order to know the effect of disinfection before a biofilm develops, the cooling water has been bypassed and disinfected by UV and ozone respectively, and biofilm formation and corrosion on carbon steel samples immersed in a continuous reactor have been evaluated by exposing steel samples to disinfected cooling water for 30-40 days. The formation of a biofilm on steel samples immersed in disinfected cooling water by UV was not different as compared with that in cooling water without disinfectant. It was shown that the effect of disinfection in the cooling water by UV was ineffective, neither biofilm formation nor corrosion on catbon steel could be inhibited. However, the effect of disinfection in cooling water by ozone was more effective than UV. Steel samples have been protected from corrosion when it immersed in disinfected cooling water by ozone. Different antimicrobial agents for the removal of biofilms already adhered to steel samples were effective. Antimicrobial agent A was the most effective among them, it made corrosion potentials of carbon steel be maintained at noble region and corrosion on catbon steel be inhibited . The effect of nitrite on the growth of isolated thermophilic bacteria has been carried out. The growth of strain TPH-7,TPH-9-2 could be promoted by nitrite, others were all suppressed. Under anoxic environment, strain TPH-7, TPM-8 could use nitrite as aelectron acceptor, others couldn？HH？HHt. Besides, strain TPH-2, TPH-5-2,TPH-5-4 and TPH-7 could use nitrate as a electron acceptor under anoxic environment.
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