Skip to main content


Hitachi Infrastructure Systems (Asia) Pte. Ltd.

This is an advanced sewage treatment process that promotes nitrification and uses inclusive immobilization supports.


The biological reaction tank is partitioned into an anaerobic tank and an aerobic tank, and by adding nitrifying pellets, which contain highly concentrated, immobilized microorganisms. This nitrogen treatment process promotes nitrifying reactions. This process can also be combined with physiochemical phosphorus removal methods such as biological phosphorus removal methods and adding coagulants to remove phosphorus.


  1. Simultaneous BOD/nitrogen treatment is possible with a residence period of 6-8 hours
  2. Nitrogen removal efficiency is stable, even at low temperatures
  3. Nitrogen removal efficiency is stable, even when combined with simultaneous coagulation methods

(in-house comparison)

System & device summary

Anaerobic-Anoxic-Aerobic type PEGASUS (BOD, nitrogen, phosphorus treatment)

Photograph: PEGASUS 4

Standard PEGASUS structure

Circulation-type PEGASUS (BOD, nitrogen treatment)

Image: Standard structural diagram

Image: Standard PEGASUS structural diagram

Inclusive immobilization principle

Nitrifying pellets are inclusively immobilized supports whose objective is to hold nitrifying bacteria. Each side of the cube is about 3 mm. If these supports are acclimated in an environment where nitrifying bacteria easily multiply, the nitrifying bacteria multiply on the inside surface of the supports. When they acclimate, nitrifying bacteria multiply on the inside surface of the supports.
Keeping supports where nitrifying bacteria have multiplied in an aerobic tank efficiently performs nitrification treatment.

Image: Diagram explaining the principle

Comparison with existing methods

The residence period is 6-8 hours, and the system is easy to apply to existing standard activated sludge-method treatment facilities.

Image: Diagram comparing PEGASUS to existing methods

Aerobic tank

Independent support-type PEGASUS (ammoniacal nitrogen treatment)

Photograph: PEGASUS 1

Fields of application

  • Biological reaction tank
PEGASUS is a Japan-registered trade mark of Hitachi Plant Technologies, Ltd. and the Japan Sewage Works Agency.(We are in the process of change of the name from Hitachi Plant Technologies, Ltd.)