Managing Urban Sewage - An Introductory Guide for Decision-makers


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United Nations Environment Programme
Division of Technology, Industry and Economics

Newsletter and Technical Publications
Freshwater Management Series No. 10

Managing Urban Sewage
An Introductory Guide for Decision-makers

Bureau of Sewerage, Tokyo Metropolitan Government

The construction of modern sewerage in Tokyo dates back to 1884, when a horseshoe-shaped bricklaying sewer was installed in the downtown area named Kanda, a part of the pipe is stillin use and is monumentally called the "Kanda Sewer".

Some 110 years after the Kanda Sewer was laid, the sewerage system in the ward area, which is the metropolis area, provided service to almost 100% of the population by the end of March 1995. And the regional sewerage system in suburban Tokyo area, "Tama area" covered 93% of the population by the end of March 2002.

There are thirteen treatment plants in the ward area, which receive approx. 4.6 million tons of wastewater every day, and seven plants in "Tama area" receive approx. 0.86 million tons.

The role of sewerage in Tokyo has changed and expanded in scope from age to age with changes in socioeconomic conditions, metropolis structures, and the environment.

Its fundamental roles at present are:

(1) Improving the living environment by drainage and disposal of wastewater;
(2) Preventing inundations through removal of rainwater;
(3) Preserving the quality of public water bodies.

And also, sewerage performs many other roles. It enhances water environment through recycling and advanced treatment of wastewater, conversion of sludge into resources, thermal energy is extracted from sewerage by such methods as tapping the heat in wastewater, and optical fiber communication cable channels are furnished.

In addition to these, Bureau of Sewerage, T.M.G. is carrying out the following projects as priorities to implement a desirable sewerage system in the 21st century.

(1)	Reconstruction; Part of Tokyo’s sewers has deteriorated due to aging and external physical disturbance such as unexpectedly heavy traffic above, ground subsidence, and so on. At present, the length of the sewers, which have exceeded legal service life, is about 2,000km and this number will continue to grow in future. Also, some plants have difficulties to cope with the increase of the flow of wastewater and rainwater due to improvements in living standards and land use. Therefore, reconstruction has been promoted by rehabilitating the deteriorated facilities, increasing the insufficient capacities, and upgrading of functionability.
(2)	Inundation Control; In recent years, inundation has occurred even in sewered urban areas. The cause is the fact that the land surface is covered with buildings, pavement and other structures. As a result, rainwater does not infiltrate to the ground and large amounts of rainwater that exceed sewer' capacity runs off and overflows. In order to prevent the inundation, the capacity of sewers and pumping stations needs to be augmented and the construction of rainwater storage tanks is necessary.
(3)	Improvement of combined sewer system; In the combined sewer system, which serves 82% of the total area, both rainwater and wastewater runs in the same pipe during wet weather, and in case of heavy rain, part of this overflows into the receiving waters without treatment. This is called "CSO" and poses a serious problem in preserving the water quality of public water bodies. Expansion of CSO intercepting sewers to wastewater treatment plants and installation of CSO storage tanks are being implemented for the countermeasures.

Bureau of Sewerage, T.M.G. obtained ISO14001 "the Environmental Management System" certification in its all departments and offices by December 2002. Bureau of Sewerage, T.M.G. is dedicated to create desirable water environment in Tokyo and transfer it to future generations through the daily activities stated above.

For more information contact:
Sewerage Bureau, Tokyo Metropolitan Government
Address: 2-8-1 Nishi-shinjuku, Tokyo, 163-8001,Japan
Tel: +81-3-5320-6515 Fax: +81-3-5388-1700

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