This study investigated effects of the continuous addition of a high-concentration of Ni2+ on the characteristics of bulking activated sludge as well as on the variety and recovery of their ability removing organic pollutants and ammonia in a sequencing batch reactor (SBR). To the knowledge of the authors, this is the first study to examine the changes in quantity and composition of the extracellular polymeric substances (EPS) in bulking activated sludge before and after the addition of a high-concentration of Ni2+. The correlation between these changes and the sludge characteristics was also investigated. The results showed that after a 40-day acclimation to the addition of 60 mg/L Ni2+, the ability to remove organic pollutants was recovered; but the ability to remove ammonia was not. The addition of Ni2+ made a great change in the quantity and composition of the EPS in bulking sludge, including both exterior soluble EPS (EPSs) and interior bound EPS (EPSb), showing a slight increase followed by a large decrease before reaching a steady state. The difference between the change in the amounts of EPSs and EPSb was not significant. However, among the component fractions, the change in protein content was obvious than that of polysaccharide and humic acid. (C) 2010 Elsevier B.V. All rights reserved.