To ensure that a johkasou functions as designed, johkasou should be constructed and installed properly. As medium to large-scale johkasou are built of reinforced concrete at sites of installation, the same precautions taken in constructing an ordinary wastewater treatment facility must be observed.
Most small-scale johkasou are made of plastics such as FRP (fiberglass reinforced plastic) or DCPD (Dicyclopentadiene) at factories. When installing this prefabricated johkasou, the procedure shown below should be observed. The dimensions of average-sized johkasou for individual households are shown in the tables below.
When installing a johkasou, it is important to keep it horizontal. If not, shunted or shortened flowing will occur in the johkasou and normal treatment performance will not be achieved. When the drainage pipes are not connected properly and form an inverse draft or slope due to the site location, river water from the discharge destination may flow back into the johkasou. A johkasou should be installed in a way that keeps it free from transformation and damage from the weight of earth and other weight loads, while keeping it in good condition for easily conducting operation and maintenance.
| Dimensions of typical small-scale johkasou (Anaerobic Filter - Contact Aeration Process) |
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| NUD | Width(mm) | Length(mm) | Height(mm) |
| 5 | 1,200 | 2,400 | 1,800 |
| 7 | 1,500 | 2,700 | 1,800 |
| 10 | 1,700 | 3,200 | 2,000 |
| Dimensions of small-scale compact type johkasou | |||
| NUD | Width(mm) | Length(mm) | Height(mm) |
| 5 | 980 | 2,155 | 1,750 |
| 7 | 980 | 2,775 | 1,750 |
| 10 | 1,230 | 3,115 | 1,750 |
Image source: Maezawa Industry, Co. Ltd.
Earth excavation
Excavate a hole of the necessary size to install the johkasou. Shoring may be required depending on the characteristics of soil or subsoil at the installation site. Excavation on sites with high ground water levels requires dewatering.
Foundation work
Lay down a layer of rubble that is sufficiently compacted to keep
the johkasou main unit horizontal and prevent the ground from sinking or rising.
After pouring leveling concrete, pour the base-plate reinforced concrete to facilitate the horizontal installation of the johkasou and to transmit the weight of it and the superstructure to the ground.
Installation
Install the johkasou in assigned location, making sure that it is level.
Filling water
Fill the tank with tap water to protect it against damage and deformation during backfilling, and then check for leveling and for water leaks.
Backfilling
First, tamp down the lower half and compact the earth by pouring water. Then, tamp down the upper half in the same way and fill in the space with earth to the bottom level of the inflow and outflow pipes.
Connecting pipes
After sufficiently compacting the piping pathway section, fill in with earth and connect the inflow and outflow pipes. Pay attention to the gradient of inflow and outflow pipes when installing them. Install the pipes and pits and backfill the earth.
Floor slab concrete work
Pour concrete on top of the backfilled earth to facilitate maintenance/inspection work, prevent the penetration of rainwater, and keep the johkasou from rising. This work can also be done after backfilling or connecting pipes.
Installing auxiliary equipment
Install auxiliary equipment, such as blowers and pumps, in their designated positions. The blower and other equipment that may generate vibration or noise must be installed after preparing the appropriate foundations.
Electrical work
Install a waterproof power supply especially designed for the johkasou unit, and be sure to ground it to the earth.
Test operation
After construction work is completed, check whether each unit involved in the johkasou and its auxiliary equipment operates properly. At the same time, also check to ensure the device is level, that there is no water leak and that the flow of water is correct.
