The first thing domestic sewage passes through is a grille, which is usually coarse or fine. The coarse grating is at a gap of 10-30 millimeters, and the fine grating is at a gap of about 3 millimeters. Floating and suspended matter in sewage is intercepted as it passes through here, and is transported by screw conveyor or belt conveyor to the slag dumping point, and is transported out to the landfill for landfill. After the coarse and fine grating filtration (some in the coarse grating after the fine grating before) of sewage in order to reduce the complexity of the subsequent system and energy saving, generally through the pumping station to the highest point of the whole sewage plant, and then rely on gravity flow through the subsequent treatment facilities. If the city has industrial wastewater mixed into the municipal network (domestic generally more or less mixed), domestic sewage treatment plant will need hydrolysis acidification tank for further decomposition treatment. This kind of pool is mainly to form an anaerobic environment, so that the anaerobic bacteria in the sewage macromolecular chain broken, by the way, eat some of them, at the same time, so that the sewage sediment and other inorganic matter precipitation part. Generally here there will be hydrogen sulfide, methane and other gases produced, the taste is very bad.