| In
article 7 of the sewerage law, it is prescribed the structure of sewerage
systems |
| shall
meet the technical standards set forth by the Cabinet Order. Also, in article 8 |
| it
is prescribed that the water quality discharged from sewerage systems to the
river |
| or other public water bodies or the sea shall conform to the
technical standards |
| stipulated by Cabinet Order. |
|
| Regarding these two articles, technical standards for final effluent water
quality |
| were set up in two cases. |
|
 |
|
In case the amount of rainwater has little influence to treated water
quality for separat sewer systems or combined sewer systems in fine
weather. |
|
|
|
 |
|
In case the amount of rainwater makes an impact on the treated water
quality, namely in combined sewer systems, when wastewater is
overflowedfrom weir in sewer systems or discharged to public water bodies
directry from pumping facility or from Wastewater Treatment Plants with
primary treatment like sedimentationom wet weather. |
|
|
 |
|
 |
| In case the amount of rainwater has little influence to treated water quality
for |
| separate sewer systems or combined sewer systems in fine weather |
|
| Final Effluent Water Quality |
| 1. pH |
5.8 - 8.6 |
|
| 2. number of coliform group |
3000 / cm3 or below |
| 3. Suspended Solids |
40 mg / l or below |
| 4. BOD, Phosphorus,
Nitrogen |
Standard Values conformed to
Planning |
|
Final Effluent Water Quality |
|
|
| In the Cabinet Order, it is prescribed that the Wastewater Treatment Plants
shall |
| be capable of treating the wastewater by the typical wastewater treatment method |
| shown in the following table according to the Planning Final Effluent Water |
| Quality. The official in local government in charge of controlling sewerage systems |
| should define the Planning Final Effluent Water Quality in terms of BOD, Nitrogen |
| and Phosphorus in accordance with ministerial ordinances considering the condition |
| of public water bodiesin which treated effluent water is discharged. |
|
|
| Table |
| Classification of Planning Effluent Water Quality and Typical Wastewater Treatment Method |
|
|
|
|
 |
| In case the amount of rainwater makes an impact on the treated water quality,
|
| namely in combined sewer systems, when wastewater is overflowed from weir in |
| sewer systems or discharged to public water bodies directry from pumping facility |
| or from Wastewater Treatment Plant with primary treatment like sedimentation. |
|
| The value obtained when total amount of discharged polluted matter represented |
| as BOD, from all of stormwater overflow weir and outfall of WTP or pumping |
| facility in treatment district during rainfall period is divided by total amount of |
| discharged wastewater from all of storm overflow weir and outfall of WTP or |
| pumping facility in treatment district during rainfall period should be
less than |
| 40 mg / l. |
|
| These total amounts should be measured or estimated by the method stipulated |
| by ministerial ordinances. |
|
| This regulation will be applied after 10 years from the enforcement, and
in these |
| 10 years provisional standard, 70 mg / l, is applied. |
|
|
 |
|
| Figure. Water Quality Standard for Combined Sewer System in Case the Amount
of |
| Rainwater makes an Impact on Treated Water Quality |
|
|
| [Note] |
| Basic concept for CSO control is that the discharged pollutant loads from |
| combined sewer systems shall be improved to the same or less level of pollutant |
| loads from separate sewer systems, which is supposed as substitute of combined |
| sewerage systems. Standard value, BOD 40 mg / l, was decided by considering
the |
| effluent water quality of storm sewer in separate sewer systems. Namely, standard |
| of BOD 40 mg / l is equivalent to 90 percentile of accumulated effluent
water qualities |
| of storm water sewer in rain events based on past-examined data. This value |
| approximatery equals to maximum of annual average value acquired in various |
| condition of land use and annual precipitation. |
|
|
