Sewage treatment can be divided into primary treatment, secondary treatment and tertiary treatment according to the degree of treatment.
The primary treatment is mainly to remove the solid matter in the suspended state in the sewage, and the physical method is commonly used. The BOD removal rate of the primary treated wastewater is only 20%, which is still not suitable for discharge, and secondary treatment is required. The main task of the secondary treatment is to substantially remove the colloid and dissolved organic matter in the sewage, and the BOD removal rate is 80% to 90%. Generally, the secondary treated sewage can reach the discharge standard, and the activated sludge method and the biofilm treatment method are commonly used. The purpose of the tertiary treatment is to further remove certain special pollutants, such as fluorine removal and phosphorus removal, which are advanced treatments and common chemical methods.
Sewage process selection requirements Reconstruction of existing primary treatment processes should be based on actual conditions, make full use of existing treatment facilities, and use septic tanks and contact pools in existing hospitals in structure or operation. Modifications shall be made in the way, and some facilities shall be added as necessary to improve the treatment effect as much as possible to meet the discharge standards for hospital sewage treatment.