Effects of thermal-Fe (II) activated oxone treatment on sludge dewaterability

•Fe (II), thermal, and their combination were used to activate oxone reaction.•Fe (II) was better than thermal in activating oxone to enhance filterability.•Sludge filterability was enhanced synergistically by Fe (II)-oxone at 25-35 °C.•Fulvic acid and tyrosine protein like substances in LB EPS affect sludge dewatering.

The enhanced dewaterability of waste activated sludge (WAS) by thermal, Fe (II), or thermal-Fe (II) activated oxone treatments was systematically investigated and compared. It was noted oxone oxidation induced by Fe (II) at the lowest tested temperature (25 °C) was more effective than any tested temperature alone induced oxone oxidation (25-80 °C). Temperature at mesophilic range can enhance the efficiency of Fe (II)-oxone treatment by 20%. Further increase of temperature to higher than 35 °C, e.g. 50 °C, did not remarkably improve the filterability of sludge in Fe (II)-oxone experiment. On the other hand, the worst performance was from thermophilic condition (80 °C) in Fe (II)-oxone experiment. The results demonstrated a significant combined effect of Fe (II)-oxone on improving sludge dewaterability within mild temperature ranging from 25 to 35 °C. Higher sludge filterability and flowability, as well as lower sludge viscosity were observed after treatment. The improvement of sludge dewaterability was achieved by removal of organic compounds in loosely-bound (LB) and tightly-bound (TB) extracellular polymeric substances (EPS). Furthermore, the improved sludge filterability was strongly correlated with the removal of dissolved organic matter (DOC), tyrosine-like proteins and fulvic acid-like materials in LB EPS. Economic analysis suggested the mesophilic Fe (II)-oxone treatment was promising for improving WAS dewaterability compared with the conventional thermal treatment.