Nation-wide effluent water quality standards for conservation of the living environment such as BOD, COD, suspended solids (SS), etc. are designed to address effluent from household septic tanks. This approach is used because corporations are required to discharge effluent of at least the same quality as that from household septic tanks in the unregulated areas. Standard values for BOD, COD and SS are given as the maximum and average values respectively. Violation of either the maximum or average standard is subject to fine.

Nitrogen and Phosphorus

1) National effluent standard

The national effluent standard for nitrogen and phosphorus was established on the basis of effluent water quality from septic tank systems, i.e. Jokaso, which consists of a sedimentation tank followed by a simple aerobic or anaerobic tank which overflows directly to public water areas. The national daily standard maximum for nitrogen was established at 120mg/l and at a daily average of 60mg/l. The maximum and the daily average for phosphorus were established at 16 mg/l and 8 mg/l, respectively. At least three sampling times are required including plant start up and just before operational shut down to determine the daily average value. This regulation standard for nitrogen and phosphorus is applied to the eff1uent of specified factories that discharge more than 50 m³/d of wastewater to public water bodies.

2) Temporal effluent standard

The national effluent standard is applied to all specified factories in the country. Some factories have difficulty meeting the common effluent standard, which necessitates those temporal standards be applied for a given period. Temporary effluent standards are applied to about 40 industries relative to nitrogen, and about 50 industries relative to phosphorus where wastewater is discharged directly into lakes, or into rivers connecting to lakes. Temporary standards are applied to industries that utilize nitrogen and phosphorus compounds in their production processes as raw or subsidiary materials and thus are more likely to be found in the wastewater from these factories. Temporary standards also are applied to small-scale factories that might have difficulty financing improvements to their wastewater treatment process to meet the nitrogen and phosphorus effluent standards. Up to one year is allowed for the factories to comply with the standard.

3) Stringent effluent standards

Local governments have the authority to apply more stringent Standards to factories discharging wastewater containing nitrogen and phosphorus to closed coastal areas, lakes and ponds. Comprehensive countermeasures must be taken to reduce the inflow of nitrogen and phosphorus into these water areas because several of these public waters have diverse sources of pollution (non-point sources) around the public water areas. The more stringent nitrogen and phosphorus effluent standards are designed to protect the water quality of Lake Biwa, which is the source of drinking water for the Kinki area that includes Kyoto and Osaka.