In the digestion tower of the sewage treatment plant of the Abwasserzweckverband (AZV) Heidelberg, it began to foam during the cold season a few years ago - as is the case with numerous other sewage treatment plants. This led to considerable operational disturbances. The digestion towers were only foam-free for a few months.
Fraunhofer IGB discovered that filamentous microorganisms were causing the foam. The oxygen input into the supposedly anoxic denitrification zone was identified as the cause for the seasonal occurrence of the filamentous microorganisms. By taking suitable measures, the development of the filamentous organisms could be significantly reduced and thus the formation of foam could be decreased.