In this study, the effects of dissolved oxygen concentration and sudden decrease and increase in dissolved oxygen concentration on the settleability of activated sludge was examined in lab-scale Sequencing Batch Reactor (SBR). Higher dissolved oxygen concentrations (2-5 mg/L) produced sludge with lower sludge volume index, lower turbidity of effluent and higher sedimentation velocity than lower dissolved oxygen concentrations (0.5-1 mg/L). The sudden increase and decrease in dissolved oxygen concentration caused higher sludge volume index.

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