Research Of Biofilm Formation And Corrosion Behavior Of SRB On H70Copper Alloy In2Times Concentrated Seawater

It is caused wide public concern of Microbiology Induced Corrosion (MIC) onmarine facilities by Sulfate-reducing bacteria (SRB). As a new technology of coolingequipment and materials using the concentrated seawater, seawater circulating coolingtechnology also has the corrosion damage by SRB. Current seawater circulatingcooling applied projects generally use2times concentrated seawater in our country.Salinity is higher than the original seawater, the system operating temperature and pHare easily suitable for breed and growth of the bacterium and algae. Therefore, it isstudied biofilm formation and corrosion behavior of SRB on H70copper alloy in2times concentrated seawater.It is discussed that the SRB dominant strain and Growth Rhythm in2timesconcentrated seawater using acclimation and microscopic observation technologies. Itis analyzed that the regularity of biofilm formation by SRB on H70copper alloy usingSEM, EDX and biochemical tests. Taking the detecting means of weight loss method,the open-circuit potential (OCP), AC impedance spectroscopy (EIS), polarizationcurves and metallurgical microscope, the corrosion behavior of H70copper alloy iscomparatively studied in sterile and inoculated2times concentrated seawater. Thestudy results show that:(1)For simulating the seawater circulating cooling process, the dominant SRB isprogressively domesticated and isolated from natural seawater. It belongs toDesulfotomaculum genus and has strong salt tolerance; Growth curve shows the lagphase (0-2d), the exponential growth phase (3-5d), stationary phase (6-11d), themaximum amount of bacteria reaches107/mL, while the decline phase is not veryclear. The trend of environmental factors (solution pH, dissolved oxygen (DO), sulfate) is negatively correlated with SRB growth curve. PH, DO and sulfate content show adeclining trend at the exponential growth phase and remain stable at the stationaryphase. The sulfate content remains stable at the late growth phase. It illustrates thatSRB breathes mainly by the fermentation except for sulfate, due to changes in theenvironment system.(2)The formation of SRB biofilm on H70copper alloy has gone through theprocesses of adsorption, biofilm-forming, peeling and cracking in2timesconcentrated seawater. The stage of biofilm formation includes two processes: Firstly,it is formed a dense biofilm by the adsorption of single SRB and its metabolites. Then,it becomes a complex mixture film composed of SRB, SRB metabolites and corrosionproducts. The analysis of EPS in the biofilm also shows that the protein andpolysaccharide content in EPS firstly increase and then decrease, and the change ofprotein is faster than polysaccharide. It makes the EPS hydrophobic has a firstlystrong and then weak change. Owing to the toxic effects of copper alloy, the growth ofSRB biofilm on H70copper alloy lag to the growing rate of SRB in the solution.(3)Compared to the sterile system, SRB’s growth and metabolism in2timesconcentrated seawater make the open circuit potential of H70copper alloy a clearlynegative shift. It makes the anodic dissolute quickly and accelerates the corrosionprocess of H70copper alloy. And because of the uneven distribution of SRBcolonies in the biofilm, the corrosion characteristic of H70copper alloy in2timesconcentrated seawater converts gradually to pitting mainly from the transverse cracks.The localized corrosion is severe.