Research On Initial Corrosion Of Cast Iron Pipe And Microbal Characteristic

In a variety of electrolyte and microbes, metal pipe corrosion in water supply system occurs easily, "second pollution" has caused a serious impact on the safety of water quality in water distribution process. Based on the BAR reactor, basic environmental of water supply system is simulated. The study focuses on the corrosion behavior of cast iron in a continuous flow, and an immersed corrosion experiment was used by contrast. To evaluate the corrosion state of each stage of metal, polarization curve and XRD were used to analyze the variations of the water quality. Miseq sequencing methods was used to study the diversity and difference of the microbial community structure. in the door, the outline, the composition characteristics of the microbial community was inquiried in the level of phylum, class and genus respectively. In addition, the corrosion behavior of cast iron, carbon steel and galvanized steel were analyzed in a continuous flow.The water flows into the Reactor A by a peristaltic pump and flows into Reactor B by the gravity flow. The residence time of each reactor were 8h. Rector A and B were compared to analyze the corrosion behavior and water quality at different locations. For nodular cast iron, corrosion velocity decreased in each reactor. Corrosion can cause the increase of p H and decrease of dissolved oxygen and TOC. The total iron and turbidity also increased in the process of corrosion. Iron released in forms of iron oxides or hydroxides of iron. They suspended in solution or deposited on the metal surface. Iron corrosion in the water supply system was mainly oxygen corrosion. Concentration of dissolved oxygen is the decisive factor for metal corrosion. Higher DO will accelerate the corrosion of cast iron.Affected by dissolved oxygen, in actual pipeline, corrosion rate decreased gradually along the way. In the immersed experiment, DO has a more decisive effect. Corrosion products are unstable Fe OOH in the dynamic experiment while in static group the corrosion products were mainly Fe₃O₄, Fe OOH only accounted for 13.9%.The number of microorganisms is not a decisive factor affecting the corrosion. The total number of bacteria and dissolved oxygen were in the strong correlation. When dissolved oxygen is sufficient, the total number of bacteria in static group is higher than that of the continuous group. When oxygen was not enough, the total number of bacteria in the continuous group was higher by one order. The biological community group has a significant change in both free and attached microorganisms. in the corrosion process, the diversity of free microorganisms decreased slightly and species richness and evenness were significantly improved in the attached microorganisms. For the phylum level, the biological community is mainly composed of Proteobacteria, Bacteroidetes and Firmicutes. 10 kinds of nitrate reducing bacteria were detected, nitrate reducing bacteria accounted for 18.3% 20.5% respectively in 30 and 55 days of biofilm biomass. Aerobic denitrifying bacteria occur later than the facultative anaerobic denitrification bacteria. Aerobic denitrification bacteria are still present in the anaerobic condition, and it does not affect the growth of anaerobic denitrification bacteria.Both nodular cast iron and carbon steel specimens have undergone strong corrosion, the corrosion rate of nodular cast iron is slightly lower than that of the carbon steel. Almost no corrosion was found in the galvanized steel reactor. Surface rust layer of cast iron was composed of Fe OOH, while in carbon steel samples the rust layer was γ-Fe₂O₃.