Corrosion Behavior Under Biofilm Of Metal Material In The Circulation Cooling Water System

As the rapid development of China's power industry the water resources will inevitably face the problem of extreme deprivation. The circulating cooling water is about 70 percent of the total consumption of a power plant. The cooling water quality to be used is getting worse due to water pollution and shortage of water resources. Using the correct approach to circulating water and improveing concentration ratio, plays an important role to the protection of water resources on saving water. Now reclamation of sewage water is used into cooling supplementary water in many of the power plants. The use of renewable water, particularly in urban wastewater reuse so that the cooling water systems face a more complex Microbiologically Induced Corrosion (MIC) problems, particularly caused by the sulfate-reducing bacteria(SRB). The presence and activity of SRB produce an environment which is radically different from the circulating cooling water in terms of surface properties, metal/water interface structure and chemical species, leading to localized corrosion of metal material mechanism. Though much work on the corrosion problem induced by SRB has been done, it is lack of the research focus on microcosmic initial corrosion behavior beneath the biofilms; some questions about the corrosion mechanism of the metal/biofilm interface have not been solved.In this paper, the growth curve, metabolite and morphology characteristics of SRB separated from slime in the bottom of the cooling tower were investigated. HSn70-1AB and BFe30-1-1, the most commonly used in condenser brass were for the study. The growth process of biofilms of SRB covering on metal surface was observed in-situ by atomic force microscope (AFM). The adhesive force between the tip of the probe and the surface of bacteria was measured with the force-distance curve of AFM The result showed that the adhesive force between the tip of the probe and the joint point of the cells was greater than that of the cell surface. And the biofilms were liable to be formed on the metal surface through the interaction effect of the individuals. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to research corrosion products on the surface of metal materials and the organic substance in the biofilm. Using the contact angle measurement method, the hydrophobicity of two copper alloy materials were studied.The SRB was rod-shaped morphology, flagella. The results of the observation showed that bacteria are gram-negative bacteria. The formation of biofilm, first of all, was that a single cell adsorpts to the surface, and then continuously around the SRB EPS will generate a large number of parcels, forming colonies gathered in a microbial membrane surface. The GC-MS analysis showed that there were organic acid in the organic layer extracted from the medium suspension, which changed pH of the medium.Through high-resolution AFM images can be observed individual cells in the copper surface immersed for 3d. The organic medium around SRB cells and corrosion products deposited can be found, but not a complete biofilm. On the surface of copper alloy immersing for 14d, SRB cells have gradually been covered by the corrosion product and organisms, the biofilm has been formed and has a certain thickness. The corrosion of BFe30-1-1 specimen was even more serious than HSn70-1AB specimen at the same time. The result also showed that the adhesion force between copper alloy surface and cells was enhanced by prolonging. The absorbability of SRB, either at cellar periphery or on cellular surface for the HSn70-1AB was found to be much lower when comparing to those for the BFe30-1-1. On the surface of biofilm formation, the metal surface wettability enhanced, more conducive to bacteria in the metal surface adsorption. Two copper alloy, HSn70-1AB performed more hydrophilic than BFe30-l-l.