Influence of operating conditions on extracellular polymeric substances and surface properties of sludge flocs

► Effect of operating conditions on exopolymers and sludge properties was performed. ► Two modes of reactor operation, S-mode and B-mode, were investigated. ► Polysaccharides (PS) and proteins (PN) were the main components of exopolymers. ► LB-EPS content was related to operation modes and sludge-retention time (SRT). ► PS and PN in LB-EPS and TB-EPS were both dependent of operation modes and SRT. Extracellular polymeric substances (EPSs) originating from the metabolism or lysis of microorganisms play important roles in biological wastewater treatment. It is necessary to understand the correlation between EPSs and the reactor operation and sludge-retention time (SRT) of the activated-sludge process to gain efficient operational strategies. Laboratory-scale completely mixed activated-sludge processes were used to grow the activated sludge with starch or glucose. Two modes of reactor operation, the S-mode and B-mode, were investigated. The results showed that polysaccharides and proteins were the main constituents in the EPSs. The percentage of polysaccharides (PSs) and proteins (PNs) in the loosely bound EPSs (LB-EPSs) and tightly bound EPSs (TB-EPSs) were 18–90% and 18–85%, respectively. The LB-EPS content was related to the operation modes and SRT. The LB-EPS contents in B-mode were triple that of S-mode, and the LB-EPS yield of sludge decreased at an increased SRT. The polysaccharides and proteins in the LB- and TB-EPSs were both dependent on the operation modes and SRT.