Though improvement of sewerage system is indispensable to achieve the environmental standards, the sewer served ratio of population in the 13 prefectures concerned to the Seto Inland Sea is 28 % in 1975 and 56 % in 1996. These values are little bit higher than those all over Japan, which are 23 % in 1975 and 55 % in 1996. Improvement of night soil treatment facilities has also been proceeded, since direct disposal to the Seto Inland Sea was inhibited. However, a part of the night soil is directly disposed to the ocean even now.
(1) Construction and Improvement of Sewerage Systems
The sever served population increased from 9,200,000 in 1975 to 19,790,000 in 1966 on the basis of data from the Ministry of Construction.
(2) Construction and Improvement of Night Soil Treatment Facility
The total treatment capacity in the 13 prefectures concerned increased 19,600 m3day at the beginning of 1980 to 23,000 m3day at the end of 1995.
With regard to the advanced treatment facilities, the total treatment capacity in the 13 prefectures concerned increased 6,800 m33day at the beginning of 1980 to 19,700 m3day at the end of 1995. (3) Improvement of Household Wastewater Treatment Tank (Jokaso)
On the basis of the each guideline, the household wastewater treatment tank, the combined treatment facility has been improved. Several prefectures require the advanced treatment facility to be constructed. And the appropriate maintenance including sludge withdrawal has been required.
The trends of the sewer served ratio and of the sewer served population are shown in Figure 7-11. The trends of the treatment capacity, the ratio of advanced treatment facility in night soil treatment, the population using household wastewater treatment tank and the population ratio of the combined tank are shown in Figure 7-12 and 7-13, respectively.
Note: after the data by Ministry of Construction
Figure 7-11 The Trends of Sewer Served Ratio of Population and Sewer Served Population
Note: after the data by each prefecture
Figure 7-12 The Trends of Treatment Capacity and Ratio of
Advanced
Treatment Facility in Night Soil Treatment
Note: after the data by each prefecture
Figure 7-13 The Trends of Population Using Household Wastewater
Treatment
Tank and Population Ratio of the Combined Tank