Effect Of Citrobacter Freundii On Corrosion Of Copper Alloys In Reclaimed Water

Citrobacter freundii isolated from reclaimed water was used to investigate the effect of the biofilms on corrosion behavior of copper alloys such as HSn70-1A, HSn70-1AB and BFe30-1-1. The Citrobacter freundii biofilms forming on copper alloys were characterized by Scanning electron microscopy(SEM) and energy dispersive spectroscopy (EDS).Extracellular polymeric substances (EPS)secreted by bacterial were quantitatively analyzed by biochemical methods in the present work. The influence of EPS on the corrosive electrochemical reaction occurring on the copper alloy - biofilms interface was discussed. Mechanism of bacteria adsorbed onto the surface of copper alloy materials was studied by measuring the thermodynamic parameters associated.Additionally, atomic force microscopy (AFM) and SEM/EDS were undertaken to observe the morphology of biofims and corroded samples in cooling water.The results showed that the Citrobacter freundii were rod-shaped morphology, and could reduce Sulfate as Sulfate-reducing bacteria (SRB).It seemed that Citrobacter freundii prefer to live in the cooling water than the Postgate C medium.Integrity and density of the biofilms characterized by SEM and AFM on HSn70-1A and HSn70-1AB were much better than BFe30-1-1.With the increase of immersion time, copper alloy surface polysaccharide biofilm EPS and protein content obviously increased. On the whole, in the same period, the ratio of polysaccharide and protein content in EPS were followed by:HSn70-1AB> HSn70-1A> BFe30-1-1.The ability of EPS completed with the metal ions dissolved from Substrate could accelerate the rate of the cathode and anode corrosive electrochemical reactions on the copper alloy-biofilms interface.According to the results on total surface free energiesγTot of copper alloy samples and interface free energies△GSWSTot between water and metal samples, the order of the hydrophobicity of samples with biofilms was BFe30-1-1>HSn70-1A>HSn70-1AB. Moreover, BFe30-1-1 samples were hydrophobic, while HSn70-1A and HSn70-1AB were hydrophilic.In aqueous solution, adsorption free energy△GadhTot values revealed that the order of easiness of the bacteria attached onto the initial copper alloy surface was HSn70-1AB> HSn70-1A> BFe30-1-1.After immersing in cooling water for a long time, the△GadhTot values was significantly increased, and its order was HSn70-1AB> HSn70-1A>BFe30-1-1. According to DLVO theory, the resistance for bacterial adsorbed onto BFe30-1-1 was relatively small,which means that adsorption occurs more easily than HSn70-lAB and HSn70-lA.It was probably due to dissolution of Ni2+on BFe30-1-1 surfaces, which might increase adhesion between bacteria and the surface of biofilms.SEM photos revealed that the three kinds of copper alloys were seriously corroded after immersing in the cooling water within Citrobacter freundii for 21 days.Therefore, the microbiologically influenced corrosion on copper alloys coursed by Citrobacter freundii can not be ignored.