Filamentous micro-organisms are bacteria, fungi and algae whose cells do not become detached from one another following cell division. Filaments comprised of a number of cells arise in this manner. Sometimes the cells cannot detach as they are surrounded by a sheath (a sort of cover).

About 80 different filamentous types, mainly bacteria, have been observed in activated sludge. Many filamentous types do not have a name, but a number (e.g. Type 0803 or IF-10), because their characteristics are not yet (completely) known. The abbreviation IF stands for Industrial Filament, viz. morphotypes mainly observed in industrial plants. It is known nowadays that the filamentous populations in industrial WTPs differ significantly from those in domestic plants.

Filamentous micro-organisms are present in just about every activated sludge. A massive increase in their number, however, results in bulking of activated sludge. Some species can also cause scum formation.

Below you will find some examples, click on the image button to view a higher resolution version.

Thiotrix 

(Sulfur

  granules)

Microthrix

parvicella