Type 0803
Type 0803 is a filamentous bacterium possessing the following characteristics:
- not branched;
- immobile;
- straight/slightly bent filaments. These are often attached to small pieces of inorganic material (sand grains and such like);
- filament length < 200 µm;
- cell diameters 0.7 - 0.8 µm;
- no attached growth;
- no sheath;
- septa clearly visible;
- square cells
- no sulphur storage;
- usually Gram negative;
- Neisser negative.

If the septa are not properly observed during analysis, the follow up using the identification key can lead to Type 1851 (light blue after Gram staining and much attached growth often present), H. hydrossis (thin, usually dead straight filaments) or Type 0092 (Neisser positive). N.B. See also Type 0914. Both species are probably closely related.

Occurrence in activated sludge
Type 0803 is regularly observed in activated sludge. The following process conditions are favourable to this species:
- sludge loading levels < ca. 0.2 kg BOD/kg MLSS.day;
- industrial waste water (textiles, pharmaceuticals);
- also possibly anaerobic pre-treated waste water;
- ???.
Type 0803 is frequently present, but practically never en masse, in domestic treatment plants. Pre-denitrification results in Type 0803 disappearing (and of Type 0914 also). The population shifts towards Type 0914 in Bio-P plants.

Control strategies
There is little if any experience with strategies aimed at controlling Type 0803. As Type 0803 disappears if pre-denitrification is introduced, an anoxic zone/selector seems to offer perspectives.