The aerobic granulation process is involved in the attachment of microorganisms, and the quorum sensing (QS) is supposed to play an important role in microbial attachment. In this study, the attachment potential of aerobic granular activated sludge (AGAS) and flocculent activated sludge (FAS) was investigated. Results clearly showed that AGAS had stronger attachment potential than FAS. A bioassay with NTL4 proved that N-acylhomoserine lactones (AHLs) were produced in both sludge, but the AHLs content of AGAS was significantly higher than FAS. Additionally, the extracellular polymeric substances (EPS) measurements indicated that there were more proteins and polysaccharides in the hydrophobic EPS fraction of AGAS. Besides, the bacterial community structure of AGAS differed from FAS by PCR-DGGE. Some hydrophobic bacteria, such as Flavobacterium, exclusively existed in AGAS. It was speculated that the difference of attachment potential between AGAS and FAS was derived from the divergence of AHLs, EPS and microbial community. (C) 2013 Elsevier Ltd. All rights reserved.