Utilization of the filamentous fungus Mucor circinelloides ZG-3 in improving sludge dewaterability during sludge bioleaching was evaluated in the present study. The degradation of sludge dissolved organic matter (DOM) by M. circinelloides ZG-3 shortened the period of complete oxidation of Fe2+ by Acidithiobacillus ferrooxidans LX5 from 11 days to only 4 days, and the inoculation of M. circinelloides ZG-3 into sludge improved the sludge dewaterability by 8.1 times. The sequential inoculation of M. circinelloides ZG-3 and A. ferrooxidans LX5 on day 0 and the end of day 1, respectively, was associated with a 25.9% lower sludge specific resistance to filtration (SRF) than that achieved using conventional bioleaching with A. ferrooxidans LX5 alone. In sludge bioleaching with the sequential inoculation of filamentous fungus M. circinelloides ZG-3 and A. ferrooxidans DC5, M. circinelloides ZG-3 acted to improve sludge dewaterability and decrease sludge DOM related toxicity to A. ferrooxidans LX5 by degrading toxic sludge DOM, and then A. ferrooxidans LX5 that was not negatively affected by sludge DOM toxicity could better improve sludge dewaterability. The filamentous fungus M. circinelloides ZG-3 was more efficacious than sludge DOM-degrading yeast strains such as Rhodotorula mucilaginosa R30 in enhancing sludge dewaterability during bioleaching. (C) 2015 Elsevier B.V. All rights reserved.