The population in the Tokyo Metropolitan District is approximately 33 million and their water is supplied from the dam lakes built in three watersheds, the Tone River, the Ara River, and the Tama River. All domestic wastewater from this region is treated and discharged to Tokyo Bay and the Pacific Ocean through rivers. The area’s climate is moderate and the population is enjoying four seasons. The rainy season and typhoon attack give the heavy rain, but in the other seasons droughts are experienced for which the water resource facilities had not been well prepared. In spite of 1500 mm of annual rain fall, the available water resource per capita accounts only 900 m3/yr. This value is one third of the average value in Japan, because of the high population density in Tokyo. This situation leads to developing more water resource and promoting rain water harvesting and wastewater reuse (Sone, 2004).
Tokyo metropolitan government issued the plan,“Water recycle master plan”in 1999 to achieve effective use of limited water resource and to create adequate water cycle in this region. This master plan consist of four basic concepts including
“developing effective water cycle in the urban area”and the seven goals. To realize these seven goals, seventeen measures are set. Among seventeen measures, the Bureau of Sewerage Works has responsibility to promote effective use of reclaimed wastewater and to develop the large area water reuse systems. The Bureau of Sewerage Works of Tokyo is operating twenty wastewater treatment plants and they treat 580 million m3of wastewater daily in 2009 from 1.3 million residents in approximately 1100 km2of planned area. Since treated wastewater is stable in terms of quality and quantity, the Bureau is promoting wastewater reclamation and reuse as a reliable source of water in Tokyo.
Brief history of water reuse development
The wastewater reuse in Tokyo has a long history and has started in 1955. A rapid sand filtration unit was constructed after activated sludge plant in Mikawashima wastewater treatment plant and reclaimed wastewater was supplied to industries to prevent over-drafting of groundwater in Tokyo Bay area. The capacity of this first reclamation plant was 15,000 m3/d.
In the 1970s, Japan experienced severe droughts in wide areas of the country. For example, in 1978, the prolonged drought conditions in the City of Fukuoka forced citizens to accept serious water supply limitations for 283 days. These drought experiences led people to recognize reclaimed water as valuable alternative resource in urban areas. In the 1980s, the local governments undertook many planned water reuse projects and national government supported these projects by providing subsidies (Ogoshiet al., 2001; Funamizuet al., 2008).
The Ochiai wastewater treatment plant has started to supply 1400 m3/d of reclaimed wastewater polished by rapid sand filtration to high-rise buildings in Shinjuku area for toilet flushing in 1984 (Figure 12.1). This project was the first milestone in Japan of water reuse in large urban areas. In 1990s, this type of area-wide water reuse systems were constructed in the New Water Front area (Figure 12.2), the East block of Shinagawa area, Ohsaki district and Shiodome area (Figure 12.3). In 2007 the system has been expanded to the Nagata-Cho area. Nowadays in Tokyo there are seven areas where the reclaimed water from wastewater reclamation plants are used for toilet flushing and their total area covers 1137 ha. In total, 9087 m3of reclaimed water are supplied as shown in Table 12.1.
Ochiai treatment plant
Shinjuku Area
Figure 12.1 Views of the Ochiai Wastewater Reclamation Plant and the buildings supplied with recycled water in Shinjuku area (Photography credit: Tokyo Metropolitan Government).
Ariake treatment plant New water front area
Figure 12.2 Views of the Ariake Wastewater Reclamation Plant and the New Water Front area supplied with recycled water (Photography credit: Tokyo Metropolitan Government).
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The reuse has been increasing, and the percentage reached about 9% of total volume of treated wastewater in 2009. The Tokyo Bureau of Sewerage Works is now promoting water recycling for toilet flushing by means of large area water reuse systems as shown in Figures 12.1 to 12.3.
The water quality criteria for water reclamation and reuse in Tokyo are summarized in Table 12.2. Since a dual pipe distribution system is an essential part for reuse of reclaimed wastewater for toilet flushing in a building, as a measure to promote this area-wide water reuse, the Tokyo Bureau of Sewerage Works asks the owners of building to install dual pipe systems at the initial design stage when they plan to construct large buildings having certain scale and floor space.
Table 12.1 Wastewater reclamation systems in Tokyo.
Shinjuku Ochiai Rapid sand filter 3016 80 14.8
New water front Ariake Bio-filter+Ozone 2193 681 26.0
East Shinagawa Shibaura Rapid sand filter+Ozone+MF 2135 83
Ohsaki 67 41.7
Figure 12.3 Views of the Shibaura Wastewater Reclamation Plant and four urban areas supplied with recycled water (Photography credit: Tokyo Metropolitan Government).
Table 12.2 Reclaimed water quality criteria in Tokyo.
Parameter
Residual chlorine, mg/L Trace amount Trace amount .0.4 – –
Colour Not unpleasant Not unpleasant Not unpleasant ,40 ,10
Turbidity Not unpleasant Not unpleasant Not unpleasant ,10 ,5
BOD, mg/L – – ,20 ,10 ,3
Odour Not unpleasant Not unpleasant Not unpleasant Not unpleasant Not unpleasant
pH 5.8–8.6 5.8–8.6 5.8–8.6 5.8–8.6 5.8–8.6
Semi-decentralizedwaterrecyclinginmegacities
12.2 THE WATER REUSE PROJECT IN SHINJUKU AREA
General description and applications
The water reuse project in Shinjuku area started in 1984 and it supplied about 1400 m3/d of reclaimed water to nine high-rise buildings in the beginning for toilet flushing. This project was the first milestone of the area-wide water reuse in Japan. Now its customers have increased to 30 high-rise buildings and the total amount of reclaimed water is 3000 m3/d (Figure 12.4). In this project wastewater is treated and reclaimed at the Ochiai wastewater reclamation plant (see Figure 12.1).
The treatment train for the Shinjuku water reuse project is illustrated in Figure 12.5. The reclaimed water is transported to the water recycling centre located in the centre of the Shinjuku high-rise building district. The treated effluent of the plant is also used for restoration of river flow. This application of stream flow augmentation in Tokyo is described in Chapter 19.
Figure 12.4 Views of the high-rise buildings in the Shinjuku area in Tokyo supplied with recycled water for toilet flushing.
Secondary + advanced treatment
Reservoir Chlorine Pump
Water recycling centre
Tank Tank Tank
Tank Tank
Building
Flush toilet Wash basin
Ochiai treatment plant Reclaimed
water Black water
Gray water
Tap water
Figure 12.5 Schematics of the water recycling project of Shinjuku Area for toilet flushing in high-rise buildings.
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The distance from Ochiai treatment plant to the water recycling centre is 9.1 km and these two facilities are connected by three pipe lines (Figure 12.6). The recycling centre is located at the basement of the Shinjuku International Building. At the water recycling centre, reclaimed water is disinfected by chlorine and stored in the distribution reservoirs with total capacity of 2909 m3.
The chlorinated water is distributed to 30 high-rise buildings by pumps from the recycling centre. The covered area is 80 ha.
The buildings have a dual water distribution system consisting of receiving tank and distribution pipes. One distribution system is for tap water from Tokyo metropolitan water supply system and it covers wash basins, tea service area and restaurants in the building. The other system distributes reclaimed water for toilet flushing. The grey water from wash basin and restaurants and the black water from toilet are discharged to sewer pipe and transported to Ochiai Treatment plant.