Type 0914
Type 0914 is a filamentous bacterium possessing the following characteristics:
- not branched;
- immobile;
- straight/bowed filaments, usually along the edges of the flocs
- filament length < 200 µm;
- cell diameters 0.6 - 0.8 µm;
- no attached growth;
- no sheath;
- septa poorly visible or invisible;
- sulphur granules present in vivo;
- Gram positive;
- Neisser negative.
The short, sulphur globules filled, filaments of Type 0914 are very characteristic. The chance of confusion with species that also store sulphur is not very big. Thiothrix usually forms longer filaments and is Gram negative while Beggiatoa has a characteristic movement. If the sulphur granules are removed from Type 0914, the filaments resemble those of Type 0803. The populations of both strains are often complementary to one another. If one of them disappears the other appears and vice versa. Therefore, it is quite probable that the growth forms of Types 0914 and 0803 are of the same bacterium.

Occurrence in activated sludge
Type 0914 occurs in treatment plants where the influent contains reduced sulphur compounds and in which a sludge load less than ca. 0.2 kg BOD/kg MLSS.day is employed. The sulphur compounds can be transported with the influent, but can also arise in the plant. Pre-settling of the influent and Bio-P processes (anaerobic period) stimulate the development of Type 0914. The population is always small in plants fed with a mainly domestic influent. Many Type 0914 filaments are occasionally present in industrial plants.

Control strategy
There is little or no experience with strategies aimed at controlling Type 0914. It has, however, been established that Types 0914 and 0803 rarely occur in treatment plants where pre-denitrification has been implemented. Therefore, an anoxic zone/selector is an option. In addition, removal of sulphides from the influent will substantially weaken the competitive position of Type 0914.