The Study On The Control Of Microbial Film In Simulated Cooling Water

In cooling water systems, on account of favorable temperatures andnutritional environments, microorganisms included Corrosive microorganismcan grow and multiply rapidly. It not only could produce corrosive substances,but also led to the formation of biofilm by adsorption on the surface of metalwith Extracelluler Polymer Substances(EPS). This may readily cause seriousproblems like low heat transfer efficiency, pitting corrosion, and accidents.Sulfate reducing bacteria (SRB) is a common and main microorganisms inmicrobiologically induced corrosions(MIC), which could produce S2-and EPSto destroy the passive film on stainless steel. Stainless steel is the main materialin power plant at present. So it is important to study the control of SRBcorrosion and biofilm in cooling systems. In this paper, electrochemicalmeasurements and surface analysis techniques were used to investigate thecontrol of SRB corrosion and biofilm on the surface of304stainless steel (SS)by using chemical and phycial methods in simulatedcooling water. The primaryresults are as follows:The inhibition behaviors of glutaric dialdehyde, dodecyl dimethyl benzylammonium chloride(1227) and Kathon886techniques for SRB corrosion werestudied, respectively. Results indicated that the use of three methods could killSRB, and increased the resistances and decreased the passive current desities Ipand carrier concentration (NDand NA) of SS electrode with the increase ofglutaric dialdehyde,1227and Kathon886concentrations, showing goodinhibitive effects.The inhibition behaviors of electromagnetic, Permanent magnet andultrasound techniques for SRB corrosion were studied, respectively. Resultsindicated that the use of three methods increased the resistances and decreasedthe passive current desities of SS electrode with the increase of treating time. At5min for electromagnetic treating time,|Z|0.01grew from59.60kΩ·cm2to136.76kΩ·cm2while Ipgrew from10.66μA/cm2to1.92μA/cm2. It showedthat the three phycial methods all had good inhibitive effects.The effects of these three chemicals on the biofilm(on the surfaces of SS)adhesion characteristics were studied, respectively. Theoretical calculations of adhesive works between biofilm and SS further revealed the inhibitionmechanism of three methods. Adhesive works untreated was29.20mJ/m2.Adhesive works increased as the concentrations of glutaric dialdehyde.Adhesive works decreased gradually as the concentrations of1227and Kathon886, and reached the minimum at100mg/L, which were1.89mJ/m2and3.06mJ/m2, respectively. SEM/EDS results indicated that an uneven distributingbiofilm formed on the SS surface after immersion in non-sterile Media with8d,and biofilm on the SS surface reduced obviously after using1227and Kathon886.The effects of these three physial methods on the biofilm(on the surfacesof SS) adhesion characteristics were studied, respectively. Theoretical adhesiveworks between biofilm and SS was calculated. It showed that adhesive worksdecreased gradually as the treating time of electromagnetic, Permanent magnettechniques. And adhesive works reached the minimum at60min for treatingtime, which were1.52mJ/m2and7.94mJ/m2, respectively. When treated byultrasound technique, adhesive works Was first decreased and then increasedwithin0~30mT or30~90mT. In the same magnetic field intensity, adhesiveworks decreased as the treating time. SEM/EDS results indicated that biofilmon the SS surface reduced obviously after using electromagnetic technique,while to some extent reduced by ultrasound technique.