Research On Corrosion Of Metal Pipe By Microorganisms In Reclaimed Water Pipe

With the promotion of reclaimed water reuse technology, reclaimed water pipe network of the new expansion becomes inevitable. Reclaimed water has rich nutrients, and provides conditions for microbial breeding. Microbial growth may cause pipeline corrosion and water quality safety. Thus, exploring microbial effect on pipeline corrosion has positive significance to extend the life of the pipe network and guarantee water supply security. In this paper, the corrosion weight loss method, SEM and EDS spectrum analysis, D-100 surface contourgraph, electrochemical test methods were used to analysis microbial membrane characteristics on the surface of of Q235 B carbon steel, cast iron, and 317 L stainless steel.Ecological factors research showed that 0 to 2 days was the period of stagnation, 3 to 8 days was logarithmic phase, 9 to 10 days was stability, and 11 to 15 days was decline phase. The optimum temperature for microbial growth was 30 to 35 ?, and the optimum pH of 7.4. Regeneration of the values of dissolved oxygen, the change of conductivity, UV254 value in the water was associated with microbial metabolic activity.Corrosion weightlessness results showed that for Q235 carbon steel, biofilm inhibitted corrosion initially, but accelerated corrosion 7 days later. For cast iron, the mic robial membrane promoted corrosion from the beginning. However, stainless steel corrosion did not happen, but the action of biofilms for long-term may induce the corrosion. Microbiologically induced corrosion rate of carbon steel through the maximum value was 0.0669 mm/a on the 7th day, the biggest proportion of microbial corrosion was 55.19%. However, the biggest microbial corrosion rate of cast iron was 0.1161 mm/a on the 3th day, biggest proportion of microbial corrosion was 69.89%.Electrochemical impedance spectroscopy study results showed that the impedance spectra of the Q235 B carbon steel, cast iron, was double capacitive reactance arc, the biggest arc radius was on the 7th day. But, stainless steel presented single capacityive reactance arc, the biggest arc radius was on the 3th day. Time constant of biological membrane of carbon steel was in 1 to 5 Hz, cast iron was in 1 to 3 Hz, and stainless steel was located in more than 100 Hz. Equivalent circuit simulation results showed that the simulation values of carbon steel, cast iron, stainless steel was different due to the difference of metal corrosion process.Transmission electron microscope scanning results showed that7 days later, carbon steel, cast iron and stainless steel had formed a complete biological membrane, bolt surface surface morphology had big difference with time. EDS results indicated that the C, O elements had a massive increase on the metal surface, S element varied along with the pipe type, the dramatic rise should be related to the corrosion process on the surface of pipes. Surface profile test showed that the thickness, roughness, corrosion pit depth and roughness of the biofilm was associated much with the metal substrate. And the thickness of the biofilm and roughness was positively correlated with the corrosion pit depth and roughness.