Nostocoida limicola III
Nostocoida limicola III is a collective name for a group of filamentous species, including N. limicola II, which possess the following characteristics:
- not branched;
- immobile;
- bowed to very twisted filaments which often form into tangles. The tangles are often present inside the flocs;
- variable filament length, but usually > 200 µm;
- cell diameter 0.8 - 2.0 µm;
- no attached growth;
- no sheath;
- septa visible;
- disc shaped to round cells;
- no sulphur storage;
- usually Gram positive;
- usually Neisser positive.
The "problem" in identifying N. limicola III mainly involves the inconsistent results of the staining methods. All of the combinations (four) can be observed, mainly in sludges from industrial treatment plants. As the diameter is also variable, N. limicola III probably includes a group of mutually related strains. On account of their morphological characteristics, the N.limicola group is easily distinguishable from other filamentous bacteria.

Occurrence in activated sludge
N. limicola III is very frequently observed in activated sludge. The population in low loaded domestic plants (nutrient removal) is always small. Large populations can be present in domestic plants if the sludge load is higher (ca. 0.2 kg BOD/kg MLSS.day) or in industrial plants. As the (tangles of) filaments are often taken up in the flocs, the effect on the SVI is small, but their presence can result in the formation of scum. Although it is not yet fully established, the following process conditions are probably favourable to N. limicola III:
- sludge loading levels of 0.1
- 0.3 kg BOD/kg MLSS.day;
- industrial waste water containing many easily biodegradable compounds;
- presettling of the influent;
- low water temperatures;
- possibly also lack of nutrients;
- complete mixing in the aeration tank;
- ????.

Control strategies
The available knowledge is still fragmentary. Occasionally, an aerobic selector has been successfully used for controlling N. limicola III.