Treatment for Domestic Wastewater using Johkasou System

During the early 1960s, there was an improvement of living standards and high economic growth in Japan. As a result of this, people were seeking more affluent lifestyles and the demand for flush toilets increased drastically.

With the introduction of flush toilets, a treatment plant was designed to treat individual household wastewater from flush toilets. The improvement of the produced technology enabled the mass production of a wastewater treatment tank known as ‘Johkasou’.

What is Johkasou?

Johkasou in Japanese language means ‘purification tank’. These are commercialized wastewater treatment tanks combining both anaerobic and aerobic microorganisms. It includes a solid-liquid separation tank, an anaerobic filter bed tank, a moving bed tank or membrane bioreactor, a carrier filter tank or sedimentation tank, followed by the disinfection tank.

Johkasou products are approved by the government of Japan and they are extensively deployed across the country as a part of the government policy.

How does it work?

When it comes to decentralized wastewater treatment technology outside Japan, septic tanks are widely used in developing countries. However, those septic tanks can encounter structural, maintenance and control problems that make it difficult to ensure fully hygienic treatment of wastewater. The structure of Johkasou is convenient in terms of management and maintenance and it demonstrates excellent sewage treatment with the combination of anaerobic and aerobic treatments

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Johkasou classified by treatment capacity

According the treatment capacity, we can categorize Johkasou treatment tanks into three:

  • Small Scale Johkasou – 5 to 50 PE, or the average amount of wastewater less than 10 m3 per day.
  • Medium scale Johkasou – 51 to 500 PE, or the average amount of wastewater less than 100m3 per day.
  • Large scale Johkasou – more than 500 PE, or the average amount of wastewater more than 100m3 per day.

Advantages and features of Johkasou systems

A Johkasou can be installed in a small, unused space and does not require any complicated procedures or costs such as acquisition of a land for installation.

A small space equivalent to one parking spot is required for installation of Johkasou at each household, and it is buried out of sight underground. Furthermore, the installation time is only about one week and the investment effect is quickly realized.

Advanced treatment such as the removal of nitrogen and phosphorous is also applied.

The effluent of Johkasou is discharged to the surrounding small rivers through drainpipes and it contributes to maintaining adequate amounts of water in rivers, enhancing water circulation without causing damage to the natural scenery.

Since Johkasou is basically designed to treat the domestic wastewater of houses, there are fewer toxic substances in the treated water and sludge. This makes it possible to reuse this water for various purposes.

Johkasou is more resilient to disasters such as earthquakes because it does not have complicated piping system or huge mechanical apparatus.


Johkasou systems are required to play a considerable role not only in domestic wastewater treatment, but also in improving the aquatic environment of the country and achieving improved water recirculation.

More than 26% of sewage in Japan is treated by using these systems. Moreover, over 8 million Johkasou are successfully running in Japan and several millions are installed in other parts of the world as well, primarily in Asia.

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