Investigation On Cooling Water Microbial Fouling And Corrosion Resistance Of Modified Surface

Heat exchangers’ microbial fouling problem exists widely in energy and chemical engineering. For its many effect factors and complexed formation mechanism, at present most of micobial fouling inhabition and mitigation methods can not eliminate the microbial fouling problem completely. Technology of surface modification has provided a new way or feasibility for heat exchange equipment cooling water microbial fouling reduction and mitigation. In this article the experimental investigation of modified surface microbial fouling characteristic in microbial suspension is carried. Firstly the surface modification on carbon steel surface is realized by chemical plating, then the Ni-P electroless deposit and Ni-P-PTFE composite coating with practical application value are prepared, consequently, the surface energy and porosity of electroless deposits are measured, and by using the scratches and thermal quenching experiments, the adhesion strength of electroless deposits were analyzed, and the the stability of electroless deposits are evaluated by repeated washing test further. The results showed that most of the electroless deposits prepared are surface with strong hydrophobicity and low surface energy. The binding force between electroless deposit and carbon steel is strong, and the stability of electroless deposits is excellent, which is applicable for practical conditions.The objective microorganisms are iron bacteria and mucus production bacteria, and the electroless deposits’microbial fouling experiment is carried out, then the mass changing of electroless deposits under different process parameters and the microbial suspension OD value changes are acquired. By calculation, the corrosion mass loss and microbial fouling adhersion of electroless deposits are obtained, then the effect of electroless deposits’ surface energy and porosity on corrosion mass loss and microbial fouling adhesion are analyzed further. The salt-spray corrosion test is proceeded on electroless deposits with different process parameters, and the salt fog corrosion mass loss and macro profile are acquired, further the effect of surface energy and porosity on salt fog corrosion mass loss are analyzed. The results show that electroless deposit with lower surface energy has less microbial and salt-spray corrosion mass loss and microbial fouling adhesion, which exhibits a strong corrosion resistance and microbial fouling inhibition.For the concentration of microbial suspension changing, the effect of concentration changing on suspension adhesion ability is analyzed by using the adhesive work between surface and microbial suspension. At first, on the basis of cultivating objective bacteria, configuration the OD400 value of iron bacteria bacteria suspension is 0.2 and the OD600 value of mucus production bacteria suspension is 0.5 respectively; then, based on the bacteria suspension OD values measurement, bacteria suspension liquid surface tension and contact angle are measured by using JC2000C1 contact angle/interfacial tension meter every 12h; Finally, the adhesive work under different OD value are calculated, and the formation process of microbial fouling are analyzed by associated change analysis of OD value and bacteria suspension adhesion work.The polarization curves and electrochemical impedance spectroscopy of two electroless deposits are measured by electrochemical workstation, and the electrochemical behavior of electroless deposits in microbial suspension are analyzed subsequently. By polarization curve distribution in microbial suspension, the microbial corrosion resistance of two electroless deposits is concluded, and based on the analysis of total impedance value changing with soaking time, the surface corrosion and microbial fouling adhesion process are analyzed consequently. Results show that the self-corrosion current density of two electroless deposits are lower than carbon steel, while the impedance value of electroless deposits are greater than carbon steel. It is a good way using electroless deposits to prevent the corrosion on carbon steel. Comparing Ni-P electroless deposit and Ni-P-PTFE composite coating, Ni-P electroless deposit presents stronger corrosion resistance in microbial suspension.