This study aimed to determine whether catalytic pretreatment can be used as a method to reduce the amount of wastewater sludge. In this study, H2O2 oxidation in the presence of a heterogeneous Fe/MgO catalyst was added to the pretreatment step. Initially a laboratory-scale test showed a TCOD (total chemical oxygen demand) was reduced 27.4% during catalytic oxidation compared to 2.1% in a catalyst-free option. Catalytic pretreatment was then evaluated in a bench-scale flow-loop test. Two bench systems were composed of identical serial processes that included anaerobic digestion, aerobic digestion, and coagulating sedimentation. The only difference between the two processes was whether catalytic pretreatment of sediment sludge was used or not. Results showed that catalyst-free oxidation TCOD gradually increased from 4200 to 7800 mg/L while catalytic oxidation maintained TCOD values at 4200 ± 200 mg/L. In addition, catalytic pretreatment reduced total nitrogen from 46.9 to 41.0 mg/L and phosphate from 3.1 to 2.3 mg/L.