Construction of urban sewage treatment plant should avoid residential areas, choose low-lying, good power conditions, located in the city downstream in line with the principle of siting sewage treatment site. In the city is also known as sewage treatment plant or sewage plant. Located in the plant is often referred to as a treatment station, when the effluent is put into the city drainage pipe, the treatment station is actually a pretreatment facility. Wastewater treatment plant is a complex system consisting of a number of unit processes, the cost and efficiency of each unit process is interlinked, each other, and ultimately determine the cost and efficiency of the entire system.