Fenton and Fenton-like sludge conditioning processes have been studied intensively due to their superior efficiency in improving sludge dewaterability. But these processes inevitably produce a large quantity of Fe-rich sludge cake that induces challenges for disposal. Herein a sustainable sludge recycling strategy has been developed by using sludge-derived Fe-rich biochar as an iron source and catalyst to enhance sludge dewatering via advanced oxidation processes. Both homogeneous Fenton reactions initiated by the leached Fe2+ from the biochar, and heterogeneous Fenton reactions initiated by the bonded iron, in forms of Fe3O4, on the surface of the biochar, are revealed to contribute to the increase the amount of center dot OH generation during sludge conditioning, which further improved the release of bound water and sludge dewaterability. The stability of the dewatering performance using the new strategy is demonstrated via three consecutive reuse cycles, in which a stable water contents of dewatered sludge cakes of approximately 46.38 wt% +/- 2.88 is obtained. The iron content of the biochar becomes stable after the 2nd round recycle. A reduction of 28.39% on the total operating cost of sludge treatment could be realized when compared with the Fenton conditioning system without sludge recycling. The proposed sustainable sludge recycling strategy could realize zero disposal Fe-containing sludge, and meanwhile produce biochar that can be beneficially reused as valuable functional materials for other applications.