Effect of anaerobic conditions on activated sludge filamentous bulking in laboratory systems

The effect of anaerobic conditions on the occurrence of filamentous microorganisms in the biocenosis of activated sludge has been studied in laboratory systems. These systems consisted of an anaerobic completely mixed tank followed by an oxic one. A single oxic completely mixed tank served as a control unit. Synthetic wastewater was used incorporating glucose and ethanol as a carbon source in order to support the growth of filamentous microorganisms in completely mixed tanks. It has been demonstrated that the growth of some filamentous organisms, for instance Type 021N and Sphaerotilus natans, was suppressed under anaerobic conditions as a result of lower rates of polyphosphate depolymerization under anaerobic conditions. However, the positive effect of the anaerobiosis may be eliminated if simultaneous dissimilatory sulphate reduction occurs. In this case filamentous bulking caused by presence of such microorganisms like Thiothrix is possible.