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Combined sewer
overflow control |
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Combined sewer overflow control refers to a sewer
system that removes waste water and rainwater via the same pipes and
drains. |
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This poses a problem
in terms of water pollution and public sanitation because the
combine system allows some non-treated sewage
to flow out during rain. |
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The revision of the ordinance for
enforcement of the Sewer Law mandated completion of combined
sewer overflow control within a decade
starting FY 2004. |
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Infrastructure target: Combined sewer
overflow control improvement rate: 17% (2004) > 40%
(2007) |
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| Status of discharge of non-treated sewage |
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| Kanda River |
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| Grease ball
cast ashore in Odaiba |
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| Status of use of combined sewer overflow control |
| · 191 cities: |
cities with
10% of all sewerage (1,899 cities) |
| · 220,000
ha: |
20%
of surface area of all sewage treatment zones (about 1,370,000
ha) |
| · About
20%: |
30%
of population prevalence rate of all sewage treatment (about
68%) |
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Method to
control combined sewer overflow |
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Installation of reservoir facilities so
that sewage saved temporarily is processed later |
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Setup of infiltration facilities so that
rainwater does not enter sewers |
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Setup of screens so that sewage
flows only after removal of refuse in sewage |
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Increase in volume of sewage sent to treatment
facility, which boosts the capacity of sewage
pipes and improves the capacity to dam rain runoff |
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| Preparation of reservoir
facilities |
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| Setup of infiltration
facilities |
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| Setup of screen |
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| Improvement of sewer
pipe capacity and height of stormwater overflow weirs |
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