Based on the environmental functions and protection objectives of surface water bodies discharged from urban sewage treatment plants, as well as the treatment processes of the sewage treatment plants, standard values for conventional pollutants in basic control items are divided into primary, secondary, and tertiary standards. Primary standards are divided into Standard A and Standard B. Class I heavy metal pollutants and optional control items are not classified.
1. Level A of the First-Class Standard is the basic requirement for reuse of urban sewage treatment plant effluent. Level A of the First-Class Standard applies when sewage treatment plant effluent is diverted to rivers and lakes with low dilution capacity for urban landscape water use or general reuse. Level A of the First-Class Standard applies when urban sewage treatment plant effluent is discharged into key river basins designated by the state or provincial government, as well as into enclosed or semi-enclosed waters such as lakes and reservoirs.
2. Standard B of the first-level standard: When discharging into Class III functional water areas of surface water (excluding designated drinking water source protection areas and swimming areas) as defined in GB 3838 or Class II functional water areas of seawater as defined in GB 3097, Standard B of the first-level standard shall apply;
3. Secondary Standard: Effluent from urban sewage treatment plants discharged into surface water category IV or V functional water areas as defined in GB 3838 or seawater category III or IV functional water areas as defined in GB 3097 shall comply with the Secondary Standard.
4. Level III Standard: Wastewater treatment plants in administrative towns outside key control basins and water source protection areas shall comply with Level III standards when using primary enhanced treatment processes, based on local economic conditions and water pollution control requirements. However, space must be reserved for secondary treatment facilities to achieve the Level II standard in phases.
