The urban drainage system is an engineering facility system for collecting, transporting, treating, and discharging urban sewage and rainwater. It is an important part of urban infrastructure. It is mainly composed of indoor drainage facilities, urban drainage pipes, sewage pumping stations, sewage treatment plants, and rainwater treatment facilities. The urban drainage pipe is the link in the urban drainage system that collects and transports urban sewage and rainwater. The urban drainage system can be divided into a combined system and a separate system. The combined system refers to the collection, transportation, treatment, and discharge of domestic sewage, industrial wastewater, and rainwater in a set of pipelines. The separate system refers to the collection, transportation, treatment, and discharge of the above three types of water in two sets of pipelines, among which domestic sewage and industrial wastewater are collected by drainage pipes and enters the sewage treatment plant for treatment; rainwater enters the rainwater drainage pipe for collection and discharge to the receiving water body.
Domestic sewage contains a large amount of organic matter, and industrial wastewater is mostly production wastewater discharged by industrial and mining enterprises, chemical test wastewater of chemical enterprises, and sewage after transporting certain specific materials. This sewage has a great adverse effect on people’s health. In the process of transporting this sewage through drainage pipes, a series of biochemical reactions will occur between inorganic matter, organic matter, and bacterial microorganisms in the sewage, causing the pH of the sewage to drop to acidic, thus causing serious corrosion damage to the inner wall of the coated steel pipe. In severe cases, the coated steel pipe will leak, which will bring a series of safety problems.
Since drainage pipes are mostly in a relatively harsh environment and the sewage they transport is highly corrosive, large-diameter concrete pipes are often used. However, after long-term use, serious corrosion damage will still occur inside the coated steel pipe. Initially, people believed that the corrosion damage of concrete pipes in sewage systems was only caused by chemical reactions, but recent studies have found that acidic substances in sewage do not cause serious corrosion to concrete drainage pipes, but to coated steel pipes.
In 1945, Parker pointed out in a research report in Melbourne that biological sulfuric acid produced by the metabolism of microorganisms in drainage pipes is one of the important reasons for the serious corrosion of concrete pipes. The report also gives the mechanism of microbial corrosion of concrete. In an anaerobic environment, some reducing bacteria will cause the sulfate at the bottom of the coated steel pipe to undergo a reduction reaction, thereby generating H2S; then sulfur-oxidizing bacteria will form sulfuric acid through oxidation reactions. After the sulfuric acid penetrates into the concrete, it reacts with the Ca(OH)2 inside the concrete, decomposing the cement hydration products, thus causing corrosion of the coated steel pipe. The factors affecting the corrosion of sewage steel pipes are the same as those of clean water steel pipes, except that the concentration of these ions is higher than that of clean water.
Post time: Jun-09-2025