In this study,the effect of varied COD loading (200,400,500,600 and 800 mg L 1) on stability and recoverability of granule-based enhanced biological phosphorus removal (EBPR) system was investigated during continuously 53-d operation.Results showed that COD loading higher than 500 mg L 1 could obviously deteriorate the granular EBPR system and result in sludge bulking with filamentous bacteria.High COD loading also changed the transformation patterns of poly-b-hydroxyalkanoates (PHAs) and glycogen in metabolism process of polyphosphate-accumulating organisms (PAOs) and inhibited the EPS secretion,which completely destroyed the stability and integrality of granules.Results of FISH indicated that glycogen-accumulating organisms (GAOs) and other microorganisms had a competitive advantage over PAOs with higher COD loading.The community composition and EBPR performance were recovered irreversibly in long time operation when COD loading was higher than 500 mg L-1.