Updated: July 2002

1.Purpose

As water quality is getting worse in many water resources in Japan, musty odor, algae and ammonia nitrogen problems are common and widespread among the water supplies in Japan. The biological filtration system removes these materials and substances and improves water quality.

2. Performance

When the plant is operated at the filtration rate of 170 m/day, the water quality of the effluent from the biological filtration is as follows.
Algae: Removal approx. 60-90%
2MIB: Removal 80%
Ammonia nitrogen: Removal 80-90%

3. Characteristics

The biological filtration system is a combination of the advantage of two conventional filtration systems, which is slow sand filter and rapid sand filter.
Influent to this system is treated biologically just like a slow sand filter, and the flow rate is still as high as rapid sand filter.
The advantage of the biological filtration is:
1) Effective removal of algae and odor causing material
2) High removal of ammonia nitrogen
3) Low running cost
4) Easy maintenance and operation
5) Relatively compact compared with the other biological treatment system

4. Principle

A porous ceramics granular media is packed in a filtration chamber. Raw water passing through the chamber contacts biological film which sticks to the media. The granular media is made of high durable ceramics and has a lot of projections and holes which make the biological film easy to stick to it. The film will not be removed easily even by backwashing.

5. Subject

Water purification plant

6. Example

Ohtsu water purification plant

7. Figure (Structure)