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

1- low initial investment cost.
2-little topographic limitation .
3-johkasou treated water and sludge are easy to   reuse .
4-invaluable contribution to maintaining sufficient water in small rivers and aquatic environments near inhabited area .

Medium / large scale johkasou :
Medium / large scale johkasou among standard structure types can be divided into two group : those belonging to the biological film method group and those belonging to the activated sludge methods , conventional activated sludge process and extended aeration process

Moving bed bio film –filtration Johkasou:

This process is a combination of a moving bio film and a bio film filtration process .
The treatment method is divided into two portions

1-The upper portion is filled with granular media and   aerated as that in a moving bed biofilm .
2-The lower portion“ the biofilm  filtration “ is filled with media for the filtration of  suspended solids .   

Nitrogen removal type :

A flowchart depicting the nitrogen removal type johkasou employing the biological film. The treatment process adopted is the nitrified water recirculation type contact aeration process, which is used in the standard structure type as shown below.

a)All of the johkasous have a flow equalization

   function .
 

b)Newly developed secondary treatment equipment

   is incorporated .
 

c)Pumps and  blowers operated and controlled

   automatically.
 

d) Some of the johkasous are capable of removing

   BOD and nitrogen to concentrations of 10mg/L or

   less .
 

 
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Membrane reactor :
A membrane reactor with a micro filtration membrane module is applied to activated sludge process for separation suspended solids , instead of  the conventional sedimentation tank . The membrane reactor has some following feature .

I) High water -solid separation performance:
The water - solid  separation performance of membrane modules is unaffected by settling characteristics of activated sludge or inflow fluctuation .

II) Reduced biological reactor size :
A membrane reactor can be operated at a high MLSS concentration, this makes it possible to reduce the size of the biological reactor and generate less excess sludge .

III) Stabilization of microorganisms :
As the sludge retention time of activated sludge in a membrane reactor is very long, specific bacteria having lower growth rates, such as nitrifying bacteria and other special bacteria that can decompose specific organic matter , can multiply at a higher rate and achieve a higher concentration .

iV) Advanced treatment of wastewater :
The water that permeates from the membrane module is very clean , having no suspended solid or coli forms. In the case of small-scale johkasou, a membrane module is submerged in the aeration tank, and permeated water is sucked out by a siphon system to produce the treated water with BOD .
 

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Biofilm filtration tank johkasou :
This tank is designed for advanced treatment of domestic wastewater and for making johkasou more compact . In this tank , biological treatment by a medium with biofilm and physical filtration occur simultaneously .It is filled with granular or cylindrical media with dimensions of several millimeters to several centimeters . This tank functions as a bioreactor , aerating in the upper part of the tank and filtrating and catching suspended solids in the under  part , performing as the contact aeration tank and the sedimentation tank in the anaerobic filter- contact aeration process. Materials for the medium used in the biofilm filtration tank may be porous ceramic, polystyrene, polyurethane or polyethylene. A diffuser is installed under the supporter of the media.