In this study, photocatalysis was used to improve the dewaterability and settleability of waste activated sludge (WAS) by a solar photocatalytic reactor with transparent Ag/TiO2 film as photocatalyst. Specific resistance of filtration (SRF) and sludge volume index (SVI) were used to evaluate WAS dewaterability and settleability, respectively, and the mechanism of photocatalysis was interpreted from the changes of pellets, loosely/tightly bound extracellular polymeric substances (LB-EPS/TB-EPS), proteins (PN) and polysaccharides (PS) in WAS. Results showed that the SRF and SVI values decreased by 86.0% and 80.0%, respectively after photocatalysis treatment for 18 h. The changes of LB-EPS/TB-EPS and morphology of WAS indicated that WAS was degraded in a stepwise and mild manner, in which the sludge pellets were possibly converted into TB-EPS and then LB-EPS. Simultaneously, LB-EPS were degraded into carbon dioxide and water by Ag/TiO2 photocatalysis. (C) 2013 Elsevier Ltd. All rights reserved.