Relation between the stability of activated sludge flocs and membrane fouling in MBR: under different SRTs

A recent modified adhesion-erosion model (AE-model) was developed to evaluate stability of activated sludge flocs in membrane bioreactor (MBR). The fouling phenomena and sludge characteristics were also studied. The sludge flocs at higher sludge retain time (SRT) were found to be more stable during the shear test, with a lower shear sensitivity of 0.0199, than the sludge flocs at lower SRT, which had a higher shear sensitivity of 0.0348. There was a close correlation between membrane fouling and the shear sensitivity of sludge flocs under test conditions. The higher shear sensitivity means more primary particles, a less porous fouling layer and a relative higher filtration resistance, leading to a more severe membrane fouling. Sludge characteristics were the main factor influencing floc stability. The sludge with higher extracellular polymer substances (EPS), relative hydrophobicity (RH) and more filamentous bacteria at lower SRT might lead to more loose structure and poorer floc stability.