Urban sewage is discharged after being treated to meet standards. Do you know where the treated urban sewage goes and what is its use?

The process of general urban sewage treatment plants

The general process of first level treatment is to notify the interception well (to let the sewage enter the factory area for treatment) before entering the coarse screen (to screen out larger substances and salvage them). The sewage is raised by the sewage pump and then enters the fine screen (to screen out smaller substances and salvage them). Secondary treatment is the main process for removing organic matter, mainly removing colloidal and dissolved organic pollutants (BOD/COD substances) from wastewater, with a removal rate of over 90%. It can be likened to microorganisms consuming organic matter in wastewater. Third level treatment is the advanced treatment of wastewater, which includes the removal of nutrients and disinfection of wastewater through chlorination, ultraviolet radiation, or ozone technology, including biological denitrification and phosphorus removal, coagulation sedimentation, sand filtration, activated carbon adsorption, ion exchange, and electrodialysis.

Where have all the treated urban sewage gone

Firstly, it is necessary to meet the discharge standards. Once the treated sewage meets the Comprehensive Wastewater Discharge Standards (DB14/1928-2019), it can be discharged into the natural world. It is mainly used for urban greening water, municipal street spraying, industrial water, household toilet flushing and other non food chain processes.

In theory, sewage, like natural water sources, can be used as a water source. However, due to the different uses of water, the requirements for the types and concentrations of impurities in water are different, and the treatment requirements are also different.

Kind reminder

Irrigation in farmland must meet the "Water Quality Standards for Irrigation in Farmland" (GB0584-2021). Sewage and irrigation are two different sets of standards, and direct use of wastewater from sewage treatment plants for irrigation poses certain safety risks. Without comprehensive water quality monitoring and safety risk assessment, it cannot be used for irrigation in farmland.