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Use a Johkasou to Clean Even Daily Wastewater

  A johkasou is a device for cleaning and discharging sewage from homes without using sewers.
The difference from the sewage system is that "factory wastewater" is not treated.
  johkasou to treat all sewageMerger processing johkasou(In the Johkasou Act, " Johkasou"It's called. ) and treat only sewage from flush toiletsSingle treatment johkasou(In the Johkasou Act, "Considered johkasou"It's called. ) are available.
The amended Johkasou Act, which came into force in April, Heisei 13, prohibited the establishment of new deemed johkasou, and now only johkasou can be newly established.

  johkasou is installed in buildings of all kinds, such as detached houses, condominiums, housing complexes, schools, hospitals, offices, supermarkets, hotels, and pachinko parlors. The size of the johkasou is expressed in terms of human tanks (or the number of people to be treated). Tanks with 50 or less people are called small tanks, tanks with 51 to 500 people are medium-sized, and tanks with 501 or more people are called large tanks. By the way, the currently installed johkasou has a minimum capacity of 5 people (large enough to treat sewage for 5 people), and a maximum capacity of 38,500 people at Kansai International Airport (eventually planned to be 77,000 people).

  Johkasou's treatment performance compares favorably with sewage terminal treatment facilities, with a BOD removal rate (ratio of amount removed to inflow) of 90% or more and BOD of treated water of 20 mg/L or less. The processing technology of johkasou is progressing day by day, and as it is becoming more compact, it is attracting attention from overseas as a method that removes nitrogen and phosphorus as a countermeasure against eutrophication, a method that is compatible with the use of a disposer, and a method that uses membrane technology.

 In addition, since Heisei 20, the government has been actively promoting the development of johkasou, such as increasing the subsidy rate from 1/3 to 1/2 for eco-friendly advanced processing type and energy-saving compact johkasou.
Source: Ministry of the Environment booklet "Johkasou's Efforts to Improve Local Water Environments"
 Contaminants in domestic wastewater are 40g of BOD per person per day. Since johkasou's BOD removal rate is over 90%, the amount of BOD in the treated water is less than 4g, and the dirt in domestic wastewater is reduced in 10 parts to less than 1 part.

 On the other hand, in the case of deemed johkasou, the BOD removal rate is 65% or more, so the amount of BOD from flush toilets is 13g, but after treatment, it is less than 5g. Combined with 27g of untreated BOD from kitchens and bathrooms, a total of about 32g of BOD is discharged.

 Due to the large amount of BOD emissions from deemed johkasou, the national government, prefectural and municipal governments provide financial support to promote conversion to johkasou for users of deemed johkasou.

Travel Tips

  • BOD is a measure of how dirty water is. The higher the number, the worse the dirt, and the more likely the water is to rot (easily turn into a ditch).

  • Technological development of johkasou for single-family homes began around Showa 50, mainly at the current Japan Environmental Education Center, and installation began in Showa 59 based on the results. After that, in order to promote the spread of johkasou, a national subsidy system for installation costs was established in Showa 62, and in Showa 63, the Ministry of Construction (now the Ministry of Land, Infrastructure, Transport and Tourism) standardized the structure.
Public interest incorporated foundation
Japan Education Center of Environmental Sanitation
2-23-3 Kikugawa, Sumida-ku, Tokyo
TEL: 03-3635-4880 (Switchboard),

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