What are the primary treatment, secondary treatment and advanced treatment of urban sewage treatment?

Primary treatment is also called pretreatment.

The pretreatment process of urban sewage treatment plant usually includes grid treatment, pumping station lifting and sand settling. The purpose of grid processing is to intercept large materials to protect the normal operation of subsequent pump pipelines and equipment. The purpose of pumping water in the pump house is to raise the water head to ensure that the sewage can flow by gravity, and then continue to build various treatment structures on the ground. The purpose of desanding treatment is to remove sand, stones and large particles carried in sewage, so as to reduce its deposition in subsequent structures, prevent facilities from silting, affect efficiency, cause wear and blockage, and affect the normal operation of pipeline equipment. Primary treatment process: it is mainly a primary sedimentation tank, which aims to remove suspended solids from sewage as much as possible. Generally speaking, the primary sedimentation tank can remove about 50% of suspended solids and about 25% of BOD5.

Secondary treatment

It is mainly composed of aeration tank and secondary sedimentation tank. The aeration fan and special aeration device are used to supply oxygen to the aeration tank. The main purpose is to convert most pollutants in sewage into CO2 and H2O through microbial metabolism, which is the oxygen consumption technology. After the reaction, microorganisms in the aeration tank continuously flow into the secondary sedimentation tank with water, and the microorganisms sink to the bottom of the tank and are sent back to the front end of the aeration tank through pipelines and pumps to be mixed with the newly inflow sewage; The treated water clarified above the secondary sedimentation tank continuously flows out of the sewage plant through the outlet weir.

Advanced treatment: further treatment to meet the requirements of high-standard receiving water bodies or for special purposes such as industry. Common processes include coagulation, sedimentation and filtration. At the end of advanced treatment, there are usually chlorination requirements and contact tanks. With the high development of urban social economy, advanced treatment is the need of future development.