Major Objectives of Sewerage Systems and New Tasks for Future

1 Current Situation of Sewage Works in Japan
In Japan, the quality of public water bodies was seriously polluted by
concentration of population in urban areas and high growth of the economy
after World War II. To cope with this situation, sewage works have been
promoted intensively and systemically based on "Five-Year Program for
the Sewerage Construction" and recently "Infrastructure Intensive
Development Plan"

Through these programs, the sewered population rate has become 68% in
FY. 2004. As the progress of sewage works, we have been gradually able
to accomplish the major objectives of sewerage system such as flood
control, improvement of living condition, and preservation of water
quality.
Fig. Improvement of Water Quality in Miya River by Promotion of Sewerage Systems

The percentage of sewered population is shown in following Web Page.
Total Population and Sewered Population Rate

However, there is still regional gap of sewered population rate between
large cities of which population is high and small cities or towns of which
population is low.

Fig. Sewered Population Rate Classfied by City Population
(Regional Gap of Sewered Population Rate)
Besides it, rehabilitation and reconstruction of sewerage systems has
been becoming other important issue to be solved. Also, we are facing
new tasks for futures, upgrading of sewerage systems such as advanced
wastewater treatment, recycle of treated water and sludge, reducing the
risk in water bodies, and so on.

2. Major Objectives of Sewerage Systems and New Tasks for Future
There are mainly three principle objectives of sewerage systems.

1) Improvement of Surrounding Environment
Immediate Removal of Wastewater is the most fundamental role of
Sewerage Systems. If the wastewater generated by human activities
is not removed and remains near residential area, Public Hygiene will
not be well maintained and the living condition will become worse.
By promotion of sewerage systems, wastewater is removed immediately,
and surrounding environment is greatly improved.

2) Prevention of Flooding
Drainage of rainwater in urban area and prevention of flooding is one
of important roles of sewerage systems. In recent year, especially
with the advancement of urbanization, rainwater permeable area has
decreasedby increasing of roads area, construction of buildings and
houses, etc. As a result, stormwater runoff amount has increased,
resulting in increased occurrence of flooding. Coping with this kind
of floodingin urban area has become one of urgent issues to be solved
in Japan.

3) Preservation of Water Quality in Public Water Bodies
In 1950's and 60's, deterioration of water environment has been markedly
progressed by discharge of untreated industrial and domestic wastewater
to public water bodies.  In 1970, the Sewerage Law was amended and the
preservation of water quality in public water bodies was clearly defended
as the role of sewerage systems in the law.After that, the water quality
has been greatly improved by intensive and systematical promotion of

sewage works based on the law.

Polluted Doka Bay (1960's)

 Recovered Dokai Bay (Present)


In addition to principle objectives of sewerage systems, there are
following new tasks for future, coming along with the promotion of sewage

works.

1) Prompt Spreading of Sewerage Systems especially in rural areas
2) Promotion of Advanced Wastewater Treatment
3) Reduction and Reuse of Sewerage Sludge
4) Reuse of Treated Wastewater
5) Stormwater Control Measures especially in urban areas
6) CSO (Combined Sewer Overflow) Control
7) Effective Use and Efficient Management of Existing Sewerage
Systems such as effective use of upper space of covered WTP,
optical fiber communication cablechannels installed in the upper
part of sewer pipes, etc.
8) Rehabilitation and Reconstruction of Sewerage Facilities
9) Controlling and Reducing the Risk in Water Bodies by monitoring of chemical
substances, risk evaluation, elimination of high risk substances, etc.