Type 0961
Type 0961 is a filamentous bacterium possessing the following characteristics:
- not branched;
- immobile;
- straight/slightly bent filaments which are often strikingly transparent;
- filament length > 200 µm;
- cell diameters 1.0 - 2.0 µm;
- no attached growth;
- sheath ??;
- septa clearly visible;
- square/rectangular cells
- no sulphur storage;
- Gram negative;
- Neisser negative.
Type 0961 can be mistaken for robust Thiothrix filaments (S storage and not so transparent) and Type 1852 (cell diameter ca. 0.7 µm).

Occurrence in activated sludge
Type 0961 is not very often observed in activated sludge. The following process conditions are favourable to this species:
- sludge loading levels > approx 0.2 kg BOD/kg MLSS.day;
- waste water containing many easily biodegradable components (agroindustry);
- ????.
Information concerning this filamentous species is very limited. Type 0961 can develop en masse in industrial treatment plants. Type 0961 virtually never occurs in domestic plants with nutrient removal.

Control strategies
1. Remove deficiencies: O2 > 2 mg/l and BOD : N : P = 100 : 5 : 1.
2. Aerobic selector.
3. Anoxic zone, if sufficient nitrite/nitrate is available for the removal of the dissolved fraction from the influent through denitrification.
4. Anaerobic zone, if a combination with Bio-P processes is an option.
5. Two step configurations (aerobic/aerobic or anaerobic/aerobic).
6. Controlling symptoms.