Because of the important role of extracellular polymeric substances (EPS) in microbial aggregates, the relationship of the EPS and physico-chemical properties of aerobic granule was studied in two sequencing airlift bioreactors (SABR) using two kinds of substrates, acetate + glucose and 4-chloroaniline (4-ClA). Higher amounts of the exopolymeric protein (PN) and lower polysaccharides (PS) and DNA level were extracted from aerobic granules in the SABRs, and the variations in the PN and PN/PS of aerobic granules were higher (770% and 360%) in the SABR using 4-ClA as substrate than that in the other reactor. At the same time, suitable operating parameters (surface gas velocity at about 2.4 cm s(-1) and settling time at 5-10 min) favored EPS production and sludge granulation. Furthermore, the minimal settling velocity, hydrophobicity, surface charge increased in accordance with PN content increase, and a negative correlation between the sludge volume index (SVI) and PN content was observed. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.