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Sewage Works in Osaka, Japan

Progress and Improvement The Development of Osaka's Sewerage System

Topographical features of Osaka

Osaka City consists of Uemachi Plateau extending from south to north and the lowland area around the plateau. Thousands of years ago, Uemachi Plateau was covered with dense primeval forest and the lowland was wave-lapped inlets.
Over the years, the inlets turned into lagoons, lakes and then swamps. The city was built on the area and turned into urban area, however, its topographic feature, which consists of Uemachi Plateau and lowland area around the plateau, is unchanged.

Ancient Shoreline of Osaka

 

Taiko (Sewari) Gesui : The Basis of Osaka's Sewerage System

Sewer constructions in Osaka have started since the late 16th century.
The basis of modern Osaka was built up by the construction of Osaka Castle which commenced from 1583. The castle town, which is surrounded by waterways run through east to west, had well planned grid like streets with the main road that also runs through east to west, heading toward the castle. The houses were built along the streets and wastewater was discharged to the sewer ditches which were dug between the backs of the houses.
The sewer ditches are called "Sewari Gesui" (Back to back sewer ditches).
Many of the sewer ditches are still in use today after being covered and rehabilitated. The city of Osaka designated them as municipal cultural properties in fiscal year 2005.

Taiko (Sewari) Gesui
Osaka City in a map of 1657

History of Modern Sewerage System

Beginning in 1894, Osaka undertook the task of modernizing its entire sewer systems, a major project which included the rehabilitation of conventional sewer ditches (Sewari Gesui) and construction of new brick sewers using the modern tunneling methods. The system has been continually improved and extended ever since.
The City of Osaka has developed its sewerage system putting much emphasis on the stormwater drainage. Accordingly, Osaka City has adopted a combined sewer system which carries stormwater and sanitary wastewater in the same pipe because it can be constructed with low cost, in the period of short time.
As population became further concentrated into Osaka City and its industry has developed, the volume of sanitary wastewater increased, resulting in the pollution of surrounding rivers and sea. This led to the need for sewage treatment.
In 1925, experimental studies on sewage treatment were conducted at a full-scale pilot plant using the activated sludge process. Based on the data obtained from the experimented studies, two sewage treatment plants, Tsumori and Ebie, were constructed and commenced their operation from April 1940.
The modern sewerage systems were constructed continuously, except during World War II, and sewage treatment plants have been constructed rapidly since the mid-1950s in order to facilitate rapid expansion of the sewer network.
Osaka City's sewerage development was promoted step by step as follows.

  • development of sewer networks to prioritize covering the most municipal area
  • construction of primary settling tanks to prioritize reducing untreated sewage discharge
  • construction of reaction tanks and final settling tanks to improve effluent water quality

In result, other 10 sewage treatment plants began their operations in addition to the first two plants. Activated sludge process was employed in all the 12 sewage treatment plants in Osaka by 1982.
At present, although the sewer system has covered almost all the city area, we will continue to pursue construction of stormwater discharge facilities such as trunk sewers in order to address the flooding problems which are growing more serious due to increasing stormwater runoff resulting from rapid urbanization. Besides, we will also pursue the water quality enhancement projects and resource recycling projects so that we can reuse by-products from the sewage treatment process and create comfortable environment in urban area. As well as those projects, we pursue renewal of the aged sewerage facilities and improve quake resistance of the facilities.

The brick sewer constructed around 1894, when the history of modern sewage works started
The Tsumori Sewage Treatment Plant in the 1940's
Naniwa Grand Floodway constructed for drastic flood control measures in south eastern area of Osaka city

 

Spread of Flush Toilet System in accordance to the expansion of Sewer Network

Until about 1950, night soil was collected from individual households and utilized as fertilizers at farmlands around the city.
However, as chemical fertilizers and flushing toilet have become widely used since the 1950s, the conventional night soil disposal method fell out of use. Currently the percentage of population served by sewer service and flush toilet system is 99.9% in Osaka City.

Development of Osaka City’s Sewerage System

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