## 3 Results and Discussion
### Reactive Azo Dye Oxidation
#### 3.2.2 Effects of Various Treatment Systems  
The effects of various treatments based on oxidation systems, namely, Dark/Fuller earth, \(\mathrm{Dark/H_{2}O_{2}}\), \(\mathrm{Dark/H_{2}O_{2}}\)-Fuller earth, \(\mathrm{UV/H_{2}O_{2}}\), \(\mathrm{UV/Fuller}\) earth, and \(\mathrm{UV/H_{2}O_{2}}\)-Fuller earth, were explored to test the effect of the Fenton reaction tendency using [PERSON]'s earth as a catalyst. The efficacy of these techniques was assessed in terms of Levafix Dark Blue dye color removal, and the results are exhibited in Figure 5. The data compare the Levafix Dark Blue oxidation using the different systems at room temperature. It is clear from the data in Figure 5 that the solo \(\mathrm{H_{2}O_{2}}\) oxidation system results in the dye having oxidation efficiencies of only 7% and 38% in the dark and under ultraviolet illumination, respectively, within 20 min of the reaction time. Moreover, in the dark test and under UV illumination, the solo [PERSON]'s earth catalyst reached removal efficiencies of 26 and 39%, respectively. However, under the solo UV illumination system, the dye oxidation reached a removal rate of only 11%. In contrast, the augmented [PERSON]'s earth with hydrogen peroxide oxidative treatment could mineralize the dye to attain rates of 72 and 98% in the dark and under UV illumination, respectively. It is worth mentioning that the photo-Fenton system based on [PERSON]'s earth augmented with hydrogen peroxide achieved the highest oxidation among  
Figure 4: Effects of azo dye Levafix Dark Blue loadings on the oxidation reaction (experimental conditions: [PERSON]’s earth 1.0 g/L; \(\mathrm{H_{2}O_{2}}\) 800 mg/L; and pH 3.0).  
the investigated oxidation systems. Notably, the high removal rates of the Fenton system or the photo-Fenton system compared to those of the solo hydrogen peroxide systems or the [PERSON]'s earth systems verify the role of the Fenton reaction in eliminating dye molecules. The presence of dual reagents might explain this in the Fenton system, as they support the generation of more hydroxyl radicals. Moreover, the presence of ultraviolet light results in further hydroxyl radical production, which is the main responsibility of the oxidation system. This reaction trend was previously reported by [PERSON] et al. [13], who treated contaminated dye effluent using a modified Fenton system.  
However, with an increase in time, the Levafix Blue dye removal exhibited a slower rate since 'OH radical production declined. Contrary, a rapid initial stage of oxidation was achieved. This is due to the consumption of the reagent in the initial stage to produce hydroxyl radicals [22]. The oxidation occurred by utilizing the activation of H\({}_{2}\)O\({}_{2}\) with the metal salts present in [PERSON]'s earth in the case of the Fenton system. However, by exceeding the reaction time, a reduction in the dye rate was attained that corresponded to the decline in the presence of H\({}_{2}\)O\({}_{2}\). This is related to the hydroxyl radical formation. Moreover, this phenomenon is also exhibited in hydrogen peroxide-based systems since the amount of hydrogen peroxide reduces due to it being consumed as time proceeds. Various research data [23] have exhibited that the quick initial reaction time is due to the immediate generation of 'OH radical species. Furthermore, the lower oxidation tendency of the dark reaction test is associated with the absence of UV illumination. Thus, it initiated oxidation through the generation of more 'OH radical species. Remarkably, the [PERSON]'s earth catalyst is easily available since it is naturally abundant as a sustainable substance.