Standard structure johkasou types
Johkasou can be divided into two types according to its structures; one is standard structure types that is designed and manufactured based on the Structural Standards for Johkasou, the another one is certified structure types that is designed and manufactured freely by the johkasou manufacture, but the treatment performance should be evaluated and certified.
Small-scale johkasou
There are three treatment processes for small-scale johkasou defined by the Structural Standards for Johkasou.
An example of a johkasou structure employing an Anaerobic Filter - Contact Aeration Process, which is the most popular treatment process adopted in small-scale johkasou. Wastewater first flows into the anaerobic filter tank where plastic filters are submerged and solid matter is separated from wastewater, which then flows into the contact aeration tank.
The anaerobic filter tank is designed not only for storing the separated solid matter and sludge, but also for removing BOD and reducing the amount of sludge as the result of anaerobic digestion of anaerobic microorganisms attached to the filters. In the contact aeration tank, degradation of organic matter and oxidation of ammonia proceed with the help of aerobic microorganisms fed by air from a blower. Aerobically treated water is separated from suspended solids in the sedimentation tank, and the supernatant water is discharged after disinfection by chlorine tablets.
Middle(large)-scale johkasou (NUD exceeding 50)
Middle(large)-scale johkasou among standard structure type johkasou can be divided into two groups: those belonging to the biological film method group and those belonging to the activated sludge method group. The former includes three treatment processes: the contact aeration process, the rotating biological contactor process and the trickling filter process. The latter includes two treatment processes: conventional activated sludge process and extended aeration process. Unit equipment for each treatment process is shown in the table. In the case of the biological film method group, a sedimentation tank (NUD from 51 to 500), and a bar screen unit (including a grinder unit) followed by a flow equalization tank (NUD exceeding 100) are adopted for primary treatment. However, the latter is the only choice in the case of the activated sludge method group. When a flow equalization tank is used, a sludge thickening/storage tank (NUD from 101 to 500), or a sludge thickening tank and a sludge storage tank (NUD exceeding 500) is required.
Unit equipment of johkasou with NUD exceeding 50 (BOD removal type)
note n: NUD
