Role of hydrocyclone separator on the formation and separation of aerobic granular sludge: Evaluating granulation efficiency and simulating hydrodynamic behavior

• Hydrocyclone separator increased SVI but also decreased MLSS. • The effect of operation time of separator on granulation was weak. • The medium water velocity of 0.3 m/s was optimal for the separation. • The addition of carrier truly enhanced the granulating process. • The carrier with large particle size was proposed to be used for AGS cultivation. Recently, hydrocyclone separator is introduced into the field of aerobic granular sludge (AGS), and applied in wastewater treatment plant to recover the dense sludge. However, the function of hydrocyclone separator for AGS cultivation is still unclear. Thus, the granulating and granular separation efficiencies of hydrocyclone separator were investigated from perspectives of experiment and hydrodynamic modelling. By comparing traditional sequencing batch reactor, the introduction of hydrocyclone separator greatly decreased the mixed liquid suspended sludge by maximum 61%, although it could improve the sludge settling performance and reduce SVI, no matter operational time of separator high or low. The reason might be attributed to strong shear force and centrifugal force provided by hydrocyclone separator. Therefore, the inlet water velocity, a factor of shear stress, was studied. The medium water velocity of 0.3 m/s contributed to appropriate tangential velocity and static pressure, reaching the optimal granular separation efficiency that was larger than 97% for the particle diameter over 400 μm. Besides, carrier particles in previous studies were summarized and found to enhance AGS formation in short time (15 to 54 days). When they were combined with hydrocyclone separator for continuous AGS cultivation, the carrier particles with large particle size (GAC, ceramsite, etc) were proposed to be used, instead of biochar or graphite oxide nanoparticle. This study explored the feasibility of hydrocyclone separator to culture AGS, which is helpful to realize the continuous AGS cultivation.