Improvement of Combined Sewer System
- In combined sewer system, during rain, the discharge of untreated wastewater containing urine is becoming a social issue.
- In 2003, the sewerage law was revised and the completion of the urgent remediation measures have become mandatory. The target year for medium and small sized cities (170 cities) is 2013 and it is 2023 for large cities (21 cities).
- Using the “Guidance for efficient urgent improvement measure plan for combined sewer system (draft),” cost reduction for improvement measures is required. Also, through introduction of new technology, such as SPIRIT 21, effective and efficient measures are applied for enforcing improvement, and the task is certainly completed within the limited time provided by law.
(Urgent improvement measures of combined sewer system)
Condition of improvements and tasks of the combined sewer system
Condition of untreated sewage effluent
Measuring results in Odaiba Kaihin Koen (Tokyo)
Condition of improvement of combined sewer system《191 cities》(end of 2006)
Business implementation based on the plan
New technology on the upgrading of joint sewer system
(Technology development by SPRIT 21)
Construction of retention facilities (Rainwater pond, etc.)
Construction of infiltration facility (inlet, gutter, pavement, etc.) and
application of separated sewer system
Construction Effect (Example of Omuta City)
Principal measures for improvements
- Adoption of activated sludge process method for rainwater, which input rainwater in the latter process during rain.
- Retain by rainwater pond
- Setting a narrower slit screen with floating dirt capture device at discharge point
Maintenance Effect (Example of Omuta City)
Omuta bay area
Illustration of activated sludge process for rainwater