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Wastewater Treatment with Johkasou System

Development of Johkasou

During the period of the high economic growth from the middle of 1950s to the first half of the 1970s, people were seeking more affluent lifestyles, and the demand for flush toilets jumped dramatically. In 1960, a Japanese Industrial Standard for determining the capacity of johkasou was stipulated. In 1969, when the Structural Standards for Johkasou was enacted, the population relying on johkasou was almost equal to that served by sewerage systems. This situation continued until 1983, during which time the johkasou system became an effective measure to promote flush toilets as a sewerage system. In 1970s, small-scale gappei-shori johkasou was developed, and later made a commercial reality by johkasou manufactures. In 1980, the Structural Standards for Johkasou were revised and structural standards for johkasou over 51 NUD* were added. Subsequently, structural standards for johkasou of less than 11 NUD were added in March 1988. Since that time, it has become possible to treat domestic wastewater from both individual households and multiple dwelling houses using johkasou.

Note *NUD:number of users for designing

Image source: Housetec, Co. Ltd.

Expansion of Johkasou under the Johkasou Law

In 1983, the government authorities established a legal framework to regulate the whole process, i.e. manufacturing, installation and management of johkasou systems under one law. This law is called the Johkasou Law. It also aims to redefine the responsibilities and duties of personnel involved in the johkasou business and to establish a certification system for johkasou technicians. With this, national qualifications relating to johkasou were established. With the implementation of the Johkasou Law in 1985, the government launched an office called the Office of Johkasou Management to promote johkasou installation in 1987. Under the leadership of the government, a national subsidy program for individuals was initiated in 1987 and another national subsidy program for municipalities started in 1994 to promote installation of gappei-shori johkasou.

In 2000, the Johkasou Law was revised and tandoku-shori johkasou was deleted from the definition in the law. The revised law requires that newly installed johkasou be of the gappei-shori johkasou variety. Johkasou systems have been required to play a considerable role not only in domestic wastewater treatment, but also in improving the nation’s aquatic environments and realizing improved water recirculation.

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Various Wastewater Treatment Systems in Japan

There are several treatment systems that have been applied to the treatment of flush toilet wastewater and gray water in Japan. According to the type of wastewater treated, the facility size and administrative support, major domestic wastewater treatment systems in Japan can be classified into "Sewerage system," "Rural sewerage system" and "Johkasou system." Apart from these systems, there are two systems for night soil treatment: “Tandoku-shori johkasou” and “Night soil storage tank.” These two systems are no longer installed and are gradually being phased out.

Sewerage systems are usually constructed in urban areas, where houses, factories and office buildings are concentrated, collecting wastewater through a piping network system and treating the wastewater in a centralized manner at treatment plants. Johkasou systems are designed for treating the domestic wastewater of individual houses or one to several buildings at a decentralized manner, and are generally divided into “small-scale johkasou” and “medium/large- scale johkasou.” In terms of small-scale johkasou, these are mass-produced, easily installed with little topographic limitation and the treated water can be discharged locally.

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It was reported in fiscal 2010 that about 117.1 million people, or 92.0 percent of the total population, were using flush toilets, while the remaining 8 percent or 10.2 million people were still using vault toilets in Japan. Treatment of human excreta discharged from flush toilets is performed through sewerage treatment systems or johkasou systems with the former accounting for 69.8 percent, and the latter for 22.2 percent.

Advantages of Johkasou systems

As small-scale johkasou can be installed on a household level and treat and discharge wastewater locally, these have remarkable advantages compared to sewerage systems from the perspective of protecting the local aquatic environment and cost-benefit performance.

  • Low initial investment cost As small-scale johkasou are mass-produced, the price of johkasou can be maintained at a level for individual or household users. A johkasou can be installed in a small, unused space and requires no complicated procedures or cost, such as for the acquisition of land for installation.
  • Little topographic limitation, short installation time and early realization of the effects As a small-scale johkasou can be installed in a small, spare space the equivalent of a parking spot and the device’s inflow pipes are short, there are few topographic limitations when it comes to the installation of small-scale johkasou. It takes only a week for a typical installation. Moreover, when the johkasou begins functioning, its effect on wastewater treatment will be evident immediately.
  • Invaluable contribution to maintaining sufficient water in small rivers and aquatic environments near inhabited areas As the effluent of johkasou is discharged onsite to surrounding small rivers through drainpipes, it contributes to maintaining sufficient amounts of water in small rivers, enhancing water circulation in local areas and does not damage the natural scenery.
  • Johkasou-treated water and sludge are easy to reuse As johkasou are basically designed to treat domestic wastewater from individual houses, there are few toxic substances in johkasou-treated water and sludge. This makes it possible to reuse these for various purposes.
  • Less vulnerable to earthquakes and other disasters When earthquakes or other disasters strike, a johkasou can be functioning again very soon because it has neither a complicated piping system nor enormous mechanical apparatus. Water in johkasou may be utilized for various purposes depending on the degree of electric power and water supply recovered.

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