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.