BACKGROUND: Aerobic granular sludge is a self-immobilization biotechnology for wastewater treatment. The thermogravimetric characteristics of aerobic granules were investigated in this study. RESULTS: The strongly physically bound water in granules that developed at a salinity of 1% (in reactor R1) and S% (in reactor R2) were S% and 3%, respectively. In addition, the extracellular polymer substances (EPS) affected the bound water more significantly at a low salinity than a higher one. Based on thermogravimetric analysis (TGA), granules that developed at low salinity (such as 1% in R1) exhibited a rich diversity of organic components, and higher total EPS concentrations, inferred from the ratios of volatile solids to total solids. Additionally, the maximum weight loss rates of the granules in all reactors occurred at a temperature of around 250 degrees C and the endothermic peaks shifted to a relatively low temperature with increasing salinity regardless of the existence of EPS. CONCLUSION: Increasing the salinity in the substrates slightly decreased the bound water fraction in granules and reduced the richness of the granule components as well as the biodiversity. This study provides detailed information on the components of aerobic granule. (C) 2007 Society of Chemical Industry.