Biological wastewater treatment process generates large amounts of sludge, the treatment and disposal of which incur substantial costs. Enhancement of sludge dewaterability is of great importance for decreasing the sludge disposal cost in a wastewater treatment plant (WWTP). This study proposes an innovative conditioning approach to improve the dewaterability of the anaerobically digested sludge (ADS) collected from a full-scale WWTP for the first time. The ADS dewaterability was significantly improved in the presence of persulfate (0–1.0 g/g TS; TS: total solids) and zero valent iron (ZVI) (0–4.0 g/g TS) at neutral pH. The largest improvement of ADS dewaterability was obtained at 2.0 g ZVI/g TS and 0.5 g persulfate/g TS, under which the capillary suction time (an indicator of sludge dewaterability) was decreased by approximately 90%. Compared with the traditional Fenton process (Fe2+ + H2O2 at pH 2.0), economic analysis indicated that the ZVI–persulfate conditioning process is more economically attractive for enhancing ADS dewaterability.