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Synergistic Corrosion Mechanism Of Escherichia Coli And Pseudomonas Fluorescens On Carbon Steel

Posted on:2020-10-14Degree:MasterType:Thesis
Country:ChinaCandidate:H Y RenFull Text:PDF
GTID:2370330575464080Subject:Municipal engineering
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Microbial influenced corrosion in the natural environment is often the result of a combination of multiple microorganisms.The interaction between microorganisms leads to a change in the number of microorganisms and a change in the properties of the biofilm,which in turn has a different effect on metal corrosion than pure microorganisms.In this study,the microbial influenced corrosion of industrial circulating cooling water system pipelines with reclaimed water as supplementary water was taken as the research background.Two kinds of microorganisms commonly used in the research environment,Escherichia coli(E.coli)and Pseudomonas fluorescens(P.fluorescens)were selected as research objects.The experimental and theoretical studies were carried out to analyze the formation and compositional changes of the biofilm on the surface of carbon steel when the two microorganisms coexist,the difference in corrosion electrochemistry and the conversion effect of iron in carbon steel.The mechanism of the influence of two microorganisms coexisting on the corrosion of carbon steel was proposed.At 7 days,the biofilm of E.coli-P.fluorescens was initially formed on the surface of carbon steel with a thickness of about 35?m and a thickness of 55?m at 14 days.The number of P.fluorescens in the biofilm of E.coli-P.fluorescens after 3 days,and the amount of attachment of the two bacteria is stable after 5 days.At 14 days,the polysaccharide content of the biofilm of E.coli-P.fluorescens reached 165.09?g/cm~2,providing space for bacterial attachment.the biofilm of E.coli-P.fluorescens with biofilm of P.fluorescens is thicker and more viscous and biofilm of E.coli is less dense and the material is easy to transfer.The microbial number and extracellular polymer content in the biofilm produced by the two bacteria at a certain depth are relatively balanced and remain uniform and stable.When E.coli and P.fluorescens were in contact at the initial(24h),the open circuit potential changed little and a stable corrosion layer was not formed.At the beginning of the corrosion(14d),the open circuit potential is shifted and stabilized.After 3 days,a stable biofilm layer was formed,and the carbon steel cathode reaction was obviously suppressed.After 11 days,the cathode slope of E.coli-P.fluorescens was the largest,which effectively inhibited the carbon steel cathode reaction.The membrane resistance of E.coli-P.fluorescens was significantly higher than that of pure bacteria,indicating that the biofilm formed by the two bacteria synergistically inhibited the corrosion.P.fluorescens contributes to an increase in membrane resistance,as opposed to E.coli.The average membrane resistance of the bacteria was increased by 181.1?·cm~2 and 161.66?·cm~2 respectively compared with the simultaneous addition.The addition of bacteria to the bacteria has been significantly weakened.On the 3 days,the average corrosion rate of E.coli-P.fluorescens was larger,which promoted corrosion and inhibited carbon steel corrosion after 3 days.The number of Fe2O3and Fe3O4 peaks in P.fluorescens condition was 44.67%and 32.90%,respectively.The Fe2O3and Fe3O4 peaks in E.coli condition was less and the fitting ratio of FeOOH is36.79%.Compared with control condition,the initial corrosion products such as?-FeOOH and?-FeOOH accumulated in the E.coli condition were more,while the Fe2O3 and Fe3O4 in the P.fluorescens condition were more.E.coli and P.fluorescens synergistic corrosion mechanism of carbon steel:at 1-3 days,two bacteria began to adhere,the number of microorganisms increased,and promoted corrosion.The biofilms of the two bacteria are initially formed in 3-7 days and the content of polysaccharides is basically stable.E.coli biofilm could transmit oxygen and organic substances locally,which would help the thicker and more viscous P.fluorescens biofilm to adhere more stably.Carbon steel corrosion is inhibited.At 7-14 days,and the P.fluorescens biofilm is stably thickened to 55?m.E.coli promotes the formation of porous?-FeOOH,?-FeOOH,and P.fluorescens promotes the formation of dense Fe2O3 and Fe3O4.The two bacteria work together to make the corrosion product layer more stable and adhere to the stable biofilm to inhibit the corrosion of the carbon steel.
Keywords/Search Tags:Escherichia coli, Pseudomonas fluorescens, carbon steel, synergistic, biofilm, microbial influenced corrosion
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