Effect of Feast/Famine Conditions on Continuous Flow Aerobic Granulation

In this study, continuous flow aerobic granulation was successfully achieved in plug flow reactors (PFRs) when the number of completely stirred tank reactors (CSTRs) in series decreased from 10 to 8. It was found that the feast/famine conditions of COD and NH3 always presented in the PFR despite the great influent composition fluctuation, and the morphology of the sludge will transform from fluffy flocs to granules along with the transition from feast to famine which also leads to the sludge settleability improvement. The transformation from granules to loose and fluffy flocs during feast period may attribute to the fact that those fluffy flocs possess better organic absorption capacity thus can absorb more organic during feast period to support the bacterial growth during the famine period. Besides, it was proved in this study that flocs and granules are two phenotypes of the activated sludge, and it was the feast to famine operation that caused the transformation between these two phenotypes. Nevertheless, although phenotype of the sludge could transform from flocs to granules during the transition from feast to famine conditions, it was found that an excessive famine period may lead to granules disintegration