Improvement in settleability and dewaterability of waste activated sludge by solar photocatalytic treatment in Ag/TiO2-coated glass tubular reactor

• Photocatalysis as a new way could enhance sludge dewaterability and settleability.
• Ag/TiO2 photocatalysis significantly improved sludge dewaterability/settleability.
• Synthesized Ag/TiO2 had much higher photocatalytic activity than TiO2 under sunlight.
• Ag/TiO2 photocatalysis degraded sludge in a stepwise and mild manner.

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.