Low F/M bulking and scumming in activated sludge plants is a phenomenon which is not completely understood. Casey et al. hypothesised that low F/M bulking and scumming is caused by the denitrification intermediate nitric oxide. Based on this hypothesis, a mathematical simulation model is formulated which predicts the most important observations related to low F/M bulking and scumming: surfactants and hydrophobic substrates may lead to the proliferation of low F/M filaments, and low F/M bulking and scumming is normally not suppressed by aerobic or small anoxic selectors. Beside these well established facts, the model predicts that incomplete nitrification can cause serious low F/M bulking and scumming problems, that large anoxic selectors with complete denitrification prevent low F/M bulking and scumming and extended sludge blankets in the secondary clarifiers influence the proliferation of low F/M filaments: in completely aerobic systems in a negative way, in systems with predenitrification zones in a positive way.
Low F/M bulking and scumming: Towards a better understanding by modelling
Jürg Kappeler, René Brodmann; Low F/M bulking and scumming: Towards a better understanding by modelling. Water Sci Technol 1 January 1995; 31 (2): 225–234. doi: https://doi.org/10.2166/wst.1995.0107
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