The present study aimed to investigate the efficiency of granular activated carbon modified with ZnO nanoparticles (GAC@ZnO composite) as a catalyst for metronidazole degradation using catalytic ozonation process. The catalytical properties of GAC@ZnO composite were measured by using FESEM, FT-IR, XRD, EDX, and BET advanced techniques. Also, the effects of pH factor (3, 5, 7, 9, and 11), initial concentration of contaminant (10–30 mg/L), reaction time (5–90 min), catalyst dosage (0.2–2.5 g/L), on the catalytic ozonation process, were studied. In addition, the effects of the interfering factors on the work of ozone degradation agent and hydroxyl radicals are tested. The results of characterisation study showed a successful formation of GAC@ZnO composite with favorable catalytic properties. In addition, the GAC surface properties were enhanced by the modification with ZnO nanoparticles, where more efficient reaction sites for metronidazole degradation were created onto GAC. The degradation performance of the GAC@ZnO composite was high in which 83% of metronidazole removal was achieved in optimum conditions (pH = 11, catalyst dosage = 2 g/L, and reaction time = 30 min). In addition, the degradation rate was noticeably found to be higher in case of using catalytic ozonation process than using ozonation process alone. The kinetic degradation reactions of metronidazole followed the pseudo-first-order equation. According to the results of this model's parameters, the degradation process is occurred on or near GAC@ZnO composite surface depending on the concentration of the pollutant. From the results obtained, it can be concluded that the GAC@ZnO composite in the catalytic ozonation treatment process was efficacious catalyst as it has excellent performance toward eradication of metronidazole wastewater.
