Fig. 2-2 Waste management flow

appropriately dispose of waste (Fig. 2-2). It not only means that waste should be sanitarily disposed of, but also that waste should be disposed of so as not to become a significant environmental burden. At each stage of waste management, various technologies are employed to play an active role in improving hygiene and protecting the environment.

## (1) Technologies for night soil disposal

The disposal of night soil, or excretory substances, is the origin of waste management. From ancient times in Japan, agriculture developed around rice farming and a sanitary recycling system used to exist whereby night soil generated in urban areas was used as fertilizer in suburban villages. However, due to urbanization, which began in the mid-1950s, the population balance between urban areas and suburban villages was lost. In addition, due to the spread of chemical fertilizers and increased demand for flush toilets, the development of night soil disposal facilities and the reinforcement of sewage systems in urban areas progressed rapidly.

Due to limited finances and time, however, the reinforcement of the sewage system could not keep pace with ever-expanding demand. So, a single type private sewage treatment system (which treats only night soil) became widespread after the mid-1960s.

In 1983 the Purification Tank Law, which regulates each stage of purification tank processing, from manufacture through installation to management and maintenance, was enacted to control purification tanks. After that, a pressing need arose for reinforcing measures to be taken against one of the major causes of water pollution: domestic wastewater, and single type private sewage treatment systems, which were predominantly purification tanks. Therefore, the Purification Tank Law was revised in 2000, limiting purification tanks to combined-type private sewage treatment systems (which treat both night soil and miscellaneous drainage) and basically prohibits the installation of new single type private sewage treatment systems (Fig. 2-3).

As at the end of 2005, there were 10.93 million purification tanks (combined-type private sewage treatment systems): an increase of 310,000 (2.9% up compared to the situation at the end of 2004). The percentage of the population (diffusion rate) with purification tanks is 8.6%: an increase of 0.2% compared to the end of 2004 (8.4%).

While the sewerage wastewater treatment system was imported from Europe, purification tanks are a domestic wastewater treatment system peculiar to Japan, which was developed in consequence of the country’s long history of night soil disposal. Purification tanks treat wastewater on site, using technology that converts organic pollutants contained in wastewater into purification tank sludge, which is composed mainly of microorganisms, while mineralizing the pollutant and separating sludge from the treated water. Purification tanks (combined-type private sewage treatment systems) have the advantages that they can treat wastewater in almost the same manner as other wastewater treatment facilities, that a system for an ordinary family can be installed in a space equivalent to that of one passenger car and that these can be employed efficiently in less heavily populated areas. So, these systems play an important role in Japan, especially as a pillar of domestic wastewater and public sewerage treatment. Besides, because purification tanks treat domestic wastewater on site, there is no great change in the flow of the water channel, etc. after a tank has been installed. Thus, these tanks contribute to constructing a water cycle that is environmentally sound.

Night soil collected from houses without flush toilets and sludge collected periodically from purification tanks are sanitarily treated in night soil treatment facilities, etc. The night soil treatment facility effectively removes not only organic substances but also nitrogen and phosphorus, which cause eutrophication, pathogenic microorganisms, etc. in an enclosed sea. Some recently developed night soil treatment facilities are equipped with facilities for recycling sludge, etc.