Stable limited filamentous bulking through keeping the competition between floc-formers and filaments in balance

► A new method of limited filamentous bulking (LFB) can save energy and enhance effluent quality. ► We optimized operation factors favorable for maintaining LFB in an A/O reactor. ► The stable LFB state could be achieved by process control and sludge population optimization. ► Dominant filaments were identified as Type 0041 and Candidatus 'Microthrix parvicella'.