With the general demand for nitrification at most WWTPs, microthrix parvicella has become a major and very common problem in activated sludge plants. Microthrix parvicella occurs at low wastewater temperatures, especially in the cold season. The then typical foam is a reliable indicator. Low specific sludge loading, low effluent temperatures, and intermittent aerated and non-aerated phases promote the growth of microthrix.
Not only with regard to this filamentous organism but also to promote a activated good sludge structure, one should set the sludge retention time as low as possible. The aim is to keep it as low as possible but high enough to safely maintain the required effluent values.
Since these filaments grow slowly, an unnecessarily high sludge retention time creates a much better environment for them.


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