Nowadays one of the most significant environmental problems is related to wastewater treatment because the release of pollutants into the environment has posed a risk to natural ecosystems and human health. Therefore, it is necessary to treat wastewater in appropriately way. Three main steps are applied in wastewater treatments that are commonly called preliminary, secondary and tertiary treatment. The preliminary and secondary treatment steps are based on physical and chemical processes. However, in most cases these types of processes are not enough alone. Among tertiary process treatment, compared to the common processes used for wastewater disinfection, new methods without the formation of disinfection by-products have been recently investigated by researchers. In this sense, among advanced oxidation process (AOPs), heterogeneous photocatalysis is a powerful alternative technique to treat polluted water because it is able to mineralize many organic compounds through the generation of hydroxyl radicals thanks to the presence of a semiconductor activated by a light source. For engineering applications, the immobilization of catalyst powders onto a suitable solid inert support is required. In this work, ZnO immobilized on macroscopic polystyrene pellets has been prepared, characterized and studied in the photocatalytic treatment of four wastewaters samples coming from secondary and tertiary processes of wastewater treatment plant by leather industries. The efficiency of the system has been determined by measuring chemical oxygen demand (COD) and total organic carbon (TOC). Photocatalytic results showed in all cases a significant COD and TOC reduction, after 7 h of UV light irradiation.