Abstract: In order to maintain the anammox biomass,waterborne polyurethane( WPU) was employed as carriers to immobilize anammox sludge,as compared to polyvinyl alcohol( PVA),sodium alginate( SA)and mixture of PVA-SA. The physical stability and anaerobic ammonium oxidation activity of the granules were evaluated. The results indicate that the four immobilized granules all have higher anaerobic ammonium oxidation activity. WPU is the most suitable immobilizing material among others,because WPU granules have shown the best biological activity and physical stability. In continuous flow experiments,the physical stability and anaerobic ammonium oxidation activity of the granules were further investigated through increasing volume loading by lowering hydraulic retention time( HRT). It was found that for WPU immobilized granules,there were no increasing effluent SS and granule fracture in the 100-day operation,and the total nitrogen( TN) removal rate still reached 80% when volume loading was1. 697 kg/( m³·d). Meanwhile WPU immobilized granules showed strong capability of retaining sludgeand good stability in long-term-run. Through 16 S r DNA cloning,it was discovered that the primary ANAMMOX bacteria inside the WPU-immobilized granules were affiliated to Candidatus Brocadia fulgida( JX243641.1). As carriers,WPU protected ANAMMOX bacteria and increased biomass. However,they had no effect on bacteria and bacterial community structure.