Bulking sludge control. Kinetics, substrate storage, and process design aspects

Bulking sludge control. Kinetics, substrate storage, and process design aspects

Martins, A.M.P.

Van Loosdrecht, M.C.M. (promotor)
Heijnen, J.J. (promotor)

Applied Sciences

2004-04-13

The activated sludge process is the preferred technology for biological wastewater treatment. Despite decades of progress and operation serious operating problems still occur with this process. One major problem is the regular occurrence of excessive growth of filamentous bacteria, phenomena known as filamentous bulking sludge. Poor solid-liquid separation can occur as result of this problem, leading to effluent quality deterioration and to process failure due to uncontrollable loss of biomass with the effluent. The goal of this thesis was to achieve a better understanding of bulking sludge and the relevant factors involved. To accomplish these objectives, well-controlled laboratory scale sequencing batch reactors with mixed microbial cultures and defined substrates, were operated under different conditions. Traditionally pure culture microbiology or full scale reactor observations have been the basis for the research. The choosen process engineering approach proved to be a success to study bulking sludge. Not only filamentous bacteria grew very well under specific conditions but also the results were reproducible and trends relating sludge settleability and operational conditions were identified. Design guidelines and operation aspects were proposed to control bulking sludge, leading to more robust, reliable, predictive, and sustainable activated sludge systems. Together with a literature review, the experimental results were the basis to develop a unifying hypothesis about bulking sludge - diffusion based selection. This theory can replace the existing theory based on kinetic selection. Both bacterial morphology and substrate micro-gradients inside microbial aggregates are hypothesized as playing a dominant role in selection for bulking sludge. An individual-based model, originally developed to a biofilm system, is adapted for the first time to model the competition between different bacterial morphotypes in activated sludge flocs. The first modelling results support qualitatively the hypothesis. Several chapters in this PhD thesis have been published by commercial publishers. These chapters can only be found in publications of these publishers. Bibliographical information of these publications can be found in the different chapters.

activated sludge
bulking sludge
substrate diffusion
bacterial morphology
feeding pattern
design selector guidelines
bacterial physiology
substrate kinetics
substrate storage
biological nutrients removal
microaerophilic conditions
phosphorus accumulating organisms

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doctoral thesis

(c) 2004 A.M.P. Martins