Municipal sewage treatment

Water volume change:

In the process of human production and life, most of the used water is discharged into the sewage pipe, but this does not mean that the amount of sewage is equal to the amount of water, because sometimes the used water is not discharged into the sewage pipe, such as fire fighting, street flushing water is discharged into the rainwater pipe or evaporated, coupled with the leakage of sewage pipes, resulting in the amount of sewage less than the amount of water. The amount of sewage in general cities is about 80% to 90% of the water. In addition, in some cases, the actual amount of sewage discharged into the sewage pipe may also be greater than the amount of water given, such as groundwater infiltration through the pipe interface, rainwater inflow through the inspection well, and factories or other users do not have dispersed water supply equipment, the amount of water given by these users may not be included in the urban centralized water supply, and so on, when the sewage may be greater than the amount of water given.

In different industrial enterprises, the exclusion of industrial wastewater is very inconsistent, the industrial wastewater of some factories is uniformly discharged, but the wastewater discharge of many factories changes greatly, and even the wastewater of some individual workshops may also be discharged in a short period of time, coupled with the emergence of new processes and new products in the factory, so that the quality of urban sewage water is also constantly changing. To sum up, the change of water quality and quantity of urban sewage is also related to the development of the city, the level of people's living standards, the number of sanitary appliances, the geographical location of the city, the climate and the season.

The design size of an urban sewage treatment plant facility depends on the total amount of industrial wastewater Q2 discharged into the sewers and the amount of sewage discharged with stormwater Q3 as well as the amount of sewage discharged by the urban population using the sewers.

Process used:

Urban sewage treatment technology is the use of various facilities and equipment and process technology to separate and remove the polluting substances contained in sewage from the water, so that the harmful substances are converted into harmless substances and useful substances, the water is purified, and the resources are fully utilized.

Urban sewage treatment technology usually has physical treatment technology, chemical treatment technology, physical chemical treatment technology, biological treatment technology and so on.

Typical physical treatment technologies used in urban sewage treatment include precipitation technology, filtration technology, air flotation technology, etc.

Typical chemical and physicochemical treatment technologies include neutralization, dosing coagulation, ion exchange and so on.

Typical biological treatment techniques include aerobic oxidative decomposition and anaerobic biological fermentation.

Urban sewage treatment process is actually the application and combination of these technologies.

Urban sewage treatment process: According to the process and treatment procedures, urban sewage treatment process can be divided into pretreatment process, primary treatment process, secondary treatment process, advanced treatment process and sludge treatment process, as well as the final sludge disposal.

preconditioning

The pretreatment process of municipal sewage treatment plant usually includes grid treatment, pump house pumping and sand settling treatment. The purpose of the grating treatment is to intercept the bulk material to protect the normal operation of the subsequent pump pipeline and equipment. The purpose of pumping the pump house is to raise the water head to ensure that the sewage can be gravity through the various treatment structures built on the ground. The purpose of sand settling treatment is to remove the sand, stone and large particles contained in the sewage, so as to reduce their settlement in the subsequent structures, prevent the sand deposition of the facilities, affect the efficacy, cause wear and blockage, and affect the normal operation of pipeline equipment. Primary treatment process: mainly the primary sedimentation tank, the purpose is to settle the suspended matter in the sewage as much as possible to remove, the general primary sedimentation tank can remove about 50% of the suspended matter and about 25% of BOD5.

Secondary treatment

It is mainly composed of an aeration tank and a secondary sedimentation tank. The aeration fan and a special aeration device are used to supply oxygen to the aeration tank. The main purpose is to change most of the pollutants in the sewage into CO2 and H2O through the metabolism of microorganisms, which is the oxygen consumption technology. Microorganisms in the aeration tank continuously flow into the secondary sedimentation tank together with water after the reaction, and the microorganisms sink in the bottom of the pool, and are sent back to the front end of the aeration tank through pipes and pumps to mix with the new inflow of sewage. The treated water clarified above the secondary settling tank flows out of the sewage plant continuously through the effluent weir.