Updated: July 2002

1. Purpose

Nitrogen is effectively removed through a revolutionary biological treatment process named PEGASUS, which uses immobilized microorganisms encapsulated in bead-like pellets. PEGASUS is a nitrification/ denitrification process wherein nitrification reaction is greatly accelerated by adding the Bio-N-Cubes (nitrification pellets), which contain immobilized microorganisms in high density, into the nitrification tank of activated sludge recycling method.

2. Performance and Characteristics

BOD removal rate: 90% (200mg/l -> 20mg/l)
T-N removal rate: 67% (30mg/l -> 10mg/l)
Cost of bioreactor: 80-90% of the conventional reactor construction cost

3. Features

1) Bioreactor capacity being half of the tank of the conventional method:
The capacity of bioreactor of PEGASUS is reduced to half of that of activated sludge recycling method, whose retention time is from 12 to 16 hours.
2) Nitrogen removal rate being stable at low water temperature:
Since there is no carry-over of the nitrifying bacteria, stable nitrification is achieved even at low water temperature and stable nitrogen removal rate can be obtained throughout the year.
3) Simultaneous BOD/nitrogen treatment is possible within retention time of 6 to 8 hours:
Existing standard activated sludge treatment facilities (BOD treatment) can be easily modified to the simultaneous BOD/nitrogen treatment without increasing the capacity of aeration tank.
4)The cost of the bioreactor being reduced to 80 to 90% of that of the conventional method:
The construction cost of the bioreactor is reduced to anywhere from 80 to 90% of the reactor of the conventional method because the capacity of nitrification/denitrification tank is reduced to a half of the conventional tank.

4. Principles

1) Immobilized microorganisms:
To immobilize microorganisms in polymeric material such as polyethylene glycol and to encapsulate them into bead-like pellets is called immobilization. The immobilization process is to supply a proper habitat for useful microorganisms which are weak in the natural environment, thereby holding them at high density in the reaction tank and having them demonstrate their capacity fully.

2) Bio-N-Cube (nitrification pellet):
The nitrifying bacteria are slow in propagating and relatively difficult to be maintained at high density in suspended sludge. They are made into the bio-N-cube with the size of about 3 mm square through immobilization. By adding the Bio-N-cubes into the bioreactor, it is possible to keep the nitrifying bacteria at high density and to treat ammonia nitrogen in a short time.

5. Flowsheet (Comparison with the conventional method)

PEGASUS:

Activated sludge recycling conventional method:

6. Applications

Food manufacturing industry
Beverage/animal feed/tobacco manufacturing industry
Universal machine and device manufacturing industry
Transportation machine and device manufacturing industry, Sewage works, Waste disposal works, Medical service, Scientific research laboratories