The potential effects of potassium ferrate (K2FeO4) on sludge dewatering under different pH values (between 3 and 8) and the mechanism of its reaction were investigated in this study. Specific resistance of filtration (SRF) was used to evaluate sludge dewaterability. Sludge water distribution was measured by the drying test. Sludge floc structure was observed by microscopic examination. Soluble chemical oxygen demand (SCOD), extracellular polymeric substances (EPSs) content, sludge disintegration degree and sludge particle size were measured to explain the observed changes in sludge dewaterability. The results indicated that the potassium ferrate pretreatment at pH 3 enhanced sludge dewaterability, while potassium ferrate pretreatment caused deterioration of sludge dewaterability at pH values of 4-8. At pH 3, sludge dewaterability increased with the increase of potassium ferrate, then decreased slightly when the dosage of potassium ferrate was greater than 1200 mg/L The results showed that a potassium ferrate dosage of 1200 mg/L at pH 3 was an ideal condition, yielding maximum sludge dewaterability characteristics by generating sludge with optimal disintegration, and EPSs concentration. However, particle size changed slightly after potassium ferrate pretreatment at pH 3. (C) 2012 Elsevier B.V. All rights reserved.