Cyanophyceae
"Cyanophyceae" comprise a group of filamentous species possessing the following characteristics:
- not branched;
- immobile;
- straight/slightly bowed filaments;
- filament length > 200 µm;
- cell diameter > 2.5 µm;
- no attached growth; - sheath ???;
- septa clearly visible, unless the filaments contain much storage material (granules);
- variable cell form;
- no sulphur storage;
- usually Gram negative;
- usually Neisser negative.
Filamentous species are mainly classified on the basis of their strikingly robust filaments in this group. The cell form and the staining results can vary strongly, meaning that this group comprises different species. The inverted commas around the name mean that these filaments morphologically resemble "Cyanophyceae" but, due to their metabolic processes, differ from them considerably. Instead of photosynthesis, they use organic compounds to grow. It is known nowadays that most filamentous types, classified as "Cyanophyceae", belong to the Alphaproteobacteria. This group is presented in detail on the "Industrial Filaments" CD-ROM; see our products.

Occurrence in activated sludge
"Cyanophyceae" are not commonly observed in activated sludge. The following process conditions are favourable to these filamentous species:
- sludge loading levels > ca. 0.2 kg BOD/kg MLSS.day;
- waste water with a high content of organic acids, such as acetic acid or propionic acid;
- probably a shortage of nutrients;
- ????
This means that these filaments are hardly ever present in nutrient removal treatment plants. In industrial plants, "Cyanophyceae" can develop massively, leading to high SVI values.

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 present for the removal of the dissolved fraction from the influent through denitrification.
4. Anaerobic zone, if a combination with the Bio-P process is an option.
5. Two step configuration (aerobic/aerobic or anaerobic/ aerobic).
6. Controlling symptoms.