<p>Combined coagulant sludge that is so-called aluminium or alum-based sludge (AlS) as a side inevitable product from drinking water industry plants and hybrid Cu-based nanoparticles has been verified to display superior performance than pristine catalyst namely Cu-catalyst and single-phase AlS catalyst. Modified calcined AlS-400 and Cu-based nanoparticles outstanding to the development of a heterojunction Fenton catalyst by coupling hybrid Cu oxides with AlS-400 in a weight proportion of 1:1. The structural and morphological properties of the synthesized materials are analyzed using X-ray diffraction spectroscopy and scanning electron microscopy (SEM). Also, the photocatalytic activity of the samples is tested through treating vehicle-washing effluent under ultraviolet (UV) illumination. Then, the photo-Fenton system parameters are evaluated, and the combined catalyst showed a treatment efficiency reached to 82% removals using nature wastewater pH 7.3. Further, factorial Box–Behnken model design is used for improving the performance of the twined mixture and maximizing the removal efficiency to reach to 86%. Thermodynamic parameters and kinetic data exposed that the reaction is exhibited non-spontaneous and exothermic nature and also following second-order oxidation reaction kinetic model. Recyclability study showed the reaction exhibited high oxidation efficacy that is reached to 78% removal till the 4th replicating cycles of oxidation test compared to 86% of the fresh AlS catalyst use. Thus, this study introduces a near-neutral-pH photo-Fenton treatment using a coagulant-sludge/CuO heterojunction photocatalyst for vehicle-wash effluent, with operating conditions established by Box–Behnken optimization and multi-cycle performance confirmed. The work links catalyst performance with waste valorization in a single platform.</p>