Co-existence of Flocs and Granules in Aerobic Granular Sludge System: Performance, Microbial Community and Proteomics

•A coexistence system with 9–11% flocs was obtained.•The flocs/granules coexistence system exhibited excellent nutrient removal.•Azoarcus and Thauera were enriched in flocs, while GAO was abundant in granules.•Granules and flocs in coexistence system behaved differently on protein level.•GAO and Thauera were the main contributors to the DEPs between granules and flocs.