Relations between substrate feeding pattern and development of filamentous bacteria in activated sludge processes:

Summary Laboratory scale activated sludge systems were operated under regimes of continuous or intermittent feeding of substrate. In a previous paper it was shown that continuously operated systems resulted in the development of filamentous bacteria and bulking sludges. Intermittently fed sludges resulted in good settling. These results are now confirmed when substrates other than glucose are present in the influent, such as nutrient broth, acetate and starch. With casein deflocculation occurred. For intermittent systems the substrate removal rates were higher than for continuous systems. Based on the results a theory is presented to account for the growth of filamentous bacteria (and bulking) in continuous systems (completely mixed systems). This theory assumes that in intermittently fed systems (plug flow systems) floc forming bacteria become dominant as a result of higher substrate uptake rates and the possibility to survive a starvation phase by thriving on accumulated intracellular metabolites.