Abstract: To investigate the effect of nitrite dosage on enhancing excess sludge fermentation, the performance of the nitrite addition on excess sludge fermentation and degradation was compared under different dosing strategies, including once, batch and continuous dosing.In this study, nitrite solutions of the same amount were added to three sequencing batch reactors (SBR) in three different modes to enhance sludge fermentation for 7 d. The experimental results show that under one-time addition mode, highest peak value of nitrite accumulation is observed. The reduction of total chemical oxygen demand (TCOD) and the accumulation of soluble chemical oxygen demand (SCOD) are most significant among these reactors, indicating that high concentration nitrite effectively promotes the conversion of sludge particulate organic matter into dissolved organic matter. For the strategy of continuously dosing, no nitrite accumulation is observed but the volatile suspended solids (VSS) of the sludge present a greater reduction rate.Moreover, dewatering ability is improved when the sludge was treated under continuous nitrite feeding, which is beneficial for a further sludge reduction. This study indicates that the mode of continuous addition of nitrite is favorable for enhancing activated sludge reduction.