Influence of substrate loading intensity on floc size in activated sludge process

The activated sludge flocs size variability and their size distribution were analyzed for the flocs sizes larger than 10 μm and for different intensities (rates) of bidirectional organic loading changes. Under these conditions the distributions of floc sizes expressed as average diameter and longest dimension fitted well the log-normal model. The logarithmic average floc size variability proved to be proportional to the loading if a time delay due to the inertia of biochemical and physical processes of activated sludge was taken into account. It has also been found that flocs larger than 50 μm constituted the main source of the surface area and volume of the activated sludge. The tests performed have shown that organic loading strongly influences floc size distribution in the activated sludge process. The long-term loading changes caused larger disturbances to the floc size distribution than more rapid but shorter ones. Generally, after the substrate overload occurred, the flocs were more prone to breakup (pin-point floc effect).