The stimulation of filamentous microorganisms in activated sludge by high oxygen concentrations

A laboratory study was conducted to compare the response of an activated sludge culture proliferating in an environment where the DO concentration was maintained between 8-9 mg l^?1 to that of a culture in an environment where the DO concentration was 2 mg l^?1 when both systems were subjected to identical loading fluctuations. It was observed that in the high DO system, filamentous microorganisms became the predominate form when the suspended solids concentration dropped below a value near 4000 mg l^?1. However, no filamentous growth appeared in the alternate system until the suspended solids level dropped below 500 mg l^?1. A model is developed which proposes to explain this observation.