Modern sewage treatment technologies include a physical treatment method, a chemical treatment method and a biological treatment method. The physical and chemical treatment methods generally act as pretreatment methods in sewage treatment. And the biological treatment method acts as a main treatment process. Currently, the biological treatment method employed more frequently in sewage treatment processes of various countries is also an activated sludge method.
The activated sludge method is a sewage biological treatment process method with activated sludge as a main body. The activated sludge method is that air is constantly introduced into wastewater, after a certain time period sludge-like flocculation is formed due to reproduction of an aerobic microorganism. The sludge-like flocculation is habited thereon with microbiota with zoogloea as a main component, having a strong capability of adsorbing and oxidizing organics. Biological coagulation, adsorption and oxidization of the activated sludge are used to decompose and eliminate organic pollutants in sewage, then the sludge is separated from water, most of the sludge flows back to an aeration tank, and a redundant portion may be drained out of an activated sludge system.
A sewage treatment plant employing a sewage treatment process of the activated sludge method generally adopts the following flow taking A2O process as a example: the sewage first passes through a grid, enters a grit chamber, a primary sedimentation tank, an anaerobic tank, an anoxic tank, an aerobic tank and a secondary sedimentation tank after lifted by a water pump, finally the treated water reaching an emission standard is drained out. In a sewage treatment plant, various treatment units are generally arranged horizontally. To enable the sewage to smoothly pass through the various treatment units from front to back, a free water surface of a later treatment unit shall be lower than that of a previous treatment unit, and a height difference of these two water surfaces shall be able to satisfy head loss of the sewage passing through a connection pipeline.
This conventional sewage treatment process with a horizontal layout has the following drawbacks: (1) a large occupation of ground, as all sewage treatment constructions are laid flat on the ground, so that the sewage treatment plant occupies a large area of the ground; (2) a large head loss: as pipelines are needed to connect between various sewage treatment constructions, resulting in a certain head loss between all of the various treatment constructions; (3) a low oxygenation efficiency: since the aeration tank has a limited depth, resulting in a lower water pressure, a low oxygenation efficiency, and a large power loss; (4) more invalid structure volumes of the constructions: to ensure no overflow of sewage out of the constructions, a certain superelevation portion is left at an upper end of each construction, resulting in more invalid structure volumes of the constructions; (5) a large heat loss in winter: since all sewage treatment constructions are laid flat on the ground, thereby forming a very large water surface, resulting in a large heat loss in cold climate conditions in winter.