Domestic sewage first passes through the grille, which generally has two channels: thick and thin. The coarse grid has a gap of 11-31mm, and the fine grid has a gap of about 3mm. Floating objects and suspended substances in sewage are intercepted when passing through here, transported to the slag dump by screw conveyor or belt conveyor, and transported to the landfill site for landfill. In order to reduce the complexity and save energy of the follow-up system, the sewage filtered by thick and thin grids (some are behind the coarse grids and before the fine grids) is generally lifted to the highest point of the whole sewage plant by pumping stations, and then flows through the follow-up treatment facilities by gravity. If there is industrial wastewater mixed into the municipal pipe network in the city (generally, it is more or less mixed in China), the domestic sewage treatment plant needs hydrolysis acidification tank for further decomposition treatment. This kind of pool is mainly to form an anaerobic environment, so that anaerobic bacteria can break the macromolecular chain in the sewage and eat some by the way. At the same time, some inorganic substances such as sediment in the sewage can be precipitated. Generally, hydrogen sulfide, methane and other gases will be produced here, and the taste is very bad.