Effect of Sludge Loading and Dissolved Oxygen Concentration on Proliferation of Thiothrix and Eikelboom Types 1851 and 0041 in Activated Sludge Wastewater Treatment Plants
Melvin-Guy Adonadaga, Boateng Ampadu, Marion Martienssen

Abstract
Filamentous bacteria have been implicated in poor solids separation in activated sludge plants, a problem referred to as sludge bulking. Chemical treatment of this condition remains costly and only offers short-term remedy. In this study, two full-scale wastewater treatment plants were monitored in order to establish relationships between filamentous overgrowth and plant operational conditions with the aim to develop specific strategies for bulking control. Morphological and molecular techniques were applied for identification of dominant filamentous bacteria while plant process parameters were determined using standard methods. Low dissolved oxygen concentration (< 2.0 mg/l) and high sludge age (> 14 days) were confirmed as major factors favoring the proliferation of Thiothrixspp and Eikelboom Types 1851 and 0041 in industrial and municipal plants respectively. Additionally, the results point to a specific limiting substrate effect in the occurrence of filamentous bacteria since similar conditions resulted in the proliferation of different filaments in the various plants. An aerobic selector designed with a short hydraulic residence time and sufficient oxygen supply is a possible strategy to control bulking caused by these filaments.

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