## 4 Discussion  
The comparison between the two homogeneous photocatalytic techniques revealed that both hydrogen peroxide and persulfate achieved high removal efficiencies, demonstrating their potential as effective oxidants in advanced oxidation processes. While hydrogen peroxide exhibited slightly higher degradation rates and enabled complete decolorization within 60 min of treatment, persulfate also showed a strong performance, contributing significantly to pollutant removal. The observed differences may be attributed to variations in radical generation mechanisms and reactivity, with hydrogen peroxide producing hydroxyl radicals and persulfate generating sulfate radicals. Both radicals are highly reactive, yet their efficiency may vary depending on the specific conditions and target compounds involved. Overall, the results indicate that both oxidants are capable, with hydrogen peroxide offering a marginal advantage in terms of treatment speed and completeness. The comparison between homogenous and heterogenous techniques demonstrated that homogeneous Fenton processes exhibited a higher degradation efficiency, likely due to the rapid generation of hydroxyl radicals in the homogeneous phase, leading to more  
Figure 14: (**A**) COD reduction and (**B**) mineralization (%) of Nile Blue, in the presence of the UV/Fe\({}^{2+}\)/H\({}_{2}\)O\({}_{2}\) and the UV/Fe\({}^{2+}\)/S\({}_{2}\)O\({}_{8}\)\({}^{2-}\) systems. immediate and effective dye breakdown. However, despite their lower efficiency, heterogeneous Fenton processes offer notable advantages, particularly in terms of operational simplicity and environmental compatibility. One significant benefit of the heterogeneous system is the elimination of the stringent pH regulation typically required for the homogeneous reaction to proceed efficiently. This not only simplifies the treatment process, but also reduces the need for additional chemical inputs and subsequent neutralization steps, making heterogeneous Fenton techniques a sustainable and cost-effective alternative for practical wastewater treatment applications. Nonetheless, various challenges remain in Fenton-based systems, such as Fe\({}^{2+}\)/persulfate activation, particularly in terms of cost-effectiveness and environmental sustainability, which are key considerations for future large-scale applications. Regarding economic feasibility and environmental impact, the activation of persulfate with transition metal ions, particularly iron, offers several advantages from both economic and environmental standpoints, including enhanced degradation and mineralization rates of contaminants and operation under mild conditions. However, several limitations must be acknowledged. One of the primary challenges lies in the declining efficiency and increased cost associated with the repeated use of metal catalysts, especially in systems where catalyst recovery is difficult. Additionally, the release of metal ions into treated water can lead to secondary pollution, necessitating further treatment steps and thus raising the overall operational cost [49]. From a broader perspective, while notable progress has been made in the development and optimization of PS activation techniques, most studies to date have focused on the degradation of single-component pollutants under controlled laboratory conditions, although that wastewater is typically characterized by a complex and variable composition. As a result, there is a lack of research on PS-based treatment systems operating at full scale, with only few pilot-scale studies available in the literature [50; 51]. In terms of sustainability, the formation of toxic intermediates is possible, and, therefore, it is essential to monitor and mitigate the generation of harmful residues with appropriate pre- and post-treatment processes. In fact, bioassay findings from various studies suggest that S\({}_{2}\)0s\({}^{2-}\) exhibits a significantly greater toxicity than its decomposition product, SO\({}_{4}\)\({}^{2-}\), primarily due to the strong oxidative nature of persulfate [52].