Abstract: The starting,sustaining,and regulation of limited filamentous bulking with low dissolved oxygen and removal efficiencies of pollutants in the process are investigated based on a lab-scale A/O reactor with real domestic wastewater as the influent.Experimental results show that significant reduction of dissolved oxygen will not induce filamentous bulking with a lower organic load(F/M=0.14 kg/(kgMLSS·d));however,SVI values can be maintained at 150-300 mg/L with the normal organic load(F/M=0.24 kg/(kgMLSS·d)) when the dissolved oxygen is 0.3-0.4 mg/L.The state can also be sustained stable for long and have good controllability.Compared with the system under high dissolved oxygen,the removal efficiencies of COD and TN are improved during the period of limited filamentous bulking,and the values are 85% and 69%,respectively.Simultaneously,ammonia is completely removed.Besides,SS in the effluent decreases with increasing SVI.Aeration consumptions decrease by 17% during the period of limited filamentous bulking.Energy consumption can be effectively reduced.