Análise da influência dos agentes químicos na corrosão do filtro biológico percolador de estações de tratamento de esgoto

Abstract

The corrosion of metals, deterioration process that occur in materials due to their interactions to the environment they are exposed to, is an alarming problem in Sewer Treatment Stations. The components concentration of the effluents in the treatment stations makes the process of corrosion even worse. The equipments directly exposed to the effluents suffer fast degradation, and in this case, it is necessary to provide frequent maintenance of them. In this sense, the present project aims to study the corrosive process in specific equipment in a Sewer Treatment Starion, the rotary distributor of the percolator biological filter. To do so, samples of three different metals, including 1010 carbon steel, stainless still and galvanized steel, were exposed to the same conditions as the filter is exposed daily. With this, it was possible to calculate mass loss of each material. The samples were installed in two different treatment stations, so they can be compared in a more efficient way. At the same time, chemical analyses were made with samples of the effluents of the two different stations. In both cases, the stainless steel performed more stable results compared to the other metals, and lower corrosion rate. The carbon steel indicated linear growth in corrosion rate, while the galvanized steel presented low corrosion rate at the beginning, but significantly increase after complete degradation of the protecting layer of zinc. Regarding the chemical analyzes, it was noted that the effluent in the Cará-Cará Sewer Treatment Station has higher concentrations of sulfides and also higher alkalinity, what raises the corrosive aggressiveness of the effluent. The results also show that not only the stainless steel is the most stable metal regarding corrosion, but also that Cará-Cará’s station has the highest concentration of impurities. The higher concentration of impurities in this treatment station leads to higher corrosion rates in the samples.