Understanding the dewaterability of aerobic granular sludge formed in continuous flow bioreactors treating real domestic wastewater: Is it really better than that of activated sludge?

Abstract The continuous flow aerobic granulation technique has been successfully developed for domestic wastewater treatment. Yet, the impact of the technique on downstream sludge dewatering performance is still unknown. This study is intended to help fill this knowledge gap by providing a comprehensive examination of the dewaterability difference between aerobic granular sludge and activated sludge in response to thickening, polymer dose, and shear force effects. Four parameters, namely capillary suction time, specific resistance to filtration, compressibility, and dewatered cake dryness, were collectively employed to evaluate sludge dewaterability. Without polymer, insignificant dewaterability differences were found between aerobic granular sludge and activated sludge thickened to 3 % total solids. With polymer, the thickened aerobic granular sludge demonstrated prominently better dewaterability at an optimal polymer dose only 25 % of that for thickened activated sludge. However, it was discovered in this study that aerobic granular sludge quickly lost its dewaterability advantage upon being disintegrated under a shear force equivalent to the level used in typical industrial dewatering centrifuges. Therefore, utilities pursuing continuous flow aerobic granulation should be aware of this discovery when considering transitions from activate sludge to aerobic granular sludge and how that transition could impact dewatering process performance and equipment selection.