LOW F/M BULKING AND SCUMMING - TOWARDS A BETTER UNDERSTANDING BY MODELING

Low F/M bulking and scumming in activated sludge plants is a phenomenon which is not completely understood. Casey ct 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 Fm? 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 Fm? 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.