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Hitachi Infrastructure Systems (Asia) Pte. Ltd.

This sewage treatment system meets the needs unique to small-scale sewage treatment plants (for example, the need to be able to respond to fluctuations in inflow water amounts) and makes maintenance management easier.


Oxidation ditch (OD) systems are systems that simultaneously perform BOD/nitrogen treatment for small to medium-scale sewage treatment plants. They use simple treatment methods, which reduces construction costs and makes maintenance management easy. There are various types of aerator rotors: the screw type, vertical shaft type, underwater propeller diffuser type, and horizontal shaft type.


  1. Compact system structure
  2. Stable treatment, even for fluctuating water amounts and water quality
  3. Maintenance is easy
  4. Can be applied in cold regions
  5. Low sludge generation

(in-house comparison)

System & device summary

With the OD system, the sewage has a residence period of 24-36 hours in water circulation path reactor tanks (oval, round, and horseshoe-shaped), and is treated by the movement of activated sludge. Compared to the existing standard activated sludge method that is commonly used in major cities, our system has lower construction costs, easier maintenance management, and achieves stable treated water quality, so it is utilized nationwide in Japan as a treatment method that is appropriate for small-scale sewage. There are various aerator types: the screw type, vertical shaft type, and horizontal shaft type, etc.

Photograph: Oxidation ditch system
Oxidation ditch system

Photograph: Screw type
Screw type

Photograph: Vertical shaft type
Vertical shaft type

Photograph: Horizontal shaft type
Horizontal shaft type

Image: System structure
System structure

Fields of application

  • Small-scale treatment facilities