## 3 Results and Discussion
### Influence of Ph  
It is noteworthy to mention that pH effectively controls the behavior of AOPs [42; 53; 54]. The UV/persulfate and photo-Fenton processes are heavily dependent on the pH of a solution [55; 56; 44; 57]. In this study, the effect of initial pH on the photo-degradation of TA through both UV/persulfate (UV/PS) and photo-Fenton (UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}^{2+}\)) processes was examined at pH 3, 5, 7, 9, and 10. Figure 4 represents the changes of aromatics and TOC removals during the treatment of aqueous solutions containing 0.1 mM TA by UV/PS and photo-Fenton processes at different initial pH values. Figure 3: Effect of EtOH and t-BuOH as radical scavengers on TA degradation efficiency during (**a**) UV/persulfate and (**b**) photo-Fenton oxidation. Experimetal conditions: (**(a)** UV/PS: [TA] = 0.1 mM, [EtOH] = 50 mM, [t-BuOH] = 50 mM, [K\({}_{2}\)S\({}_{2}\)O\({}_{8}\)] = 53.1 mM, pH = 9 and T = 25 \({}^{\circ}\)C; (**b**) UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}^{2+}\): [TA] = 0.1 mM, [t-BuOH] = 10 mM, [H\({}_{2}\)O\({}_{2}\)] = 29.4 mM, [Fe\({}^{2+}\)] = 0.18 mM, pH = 3, and T = 25 \({}^{\circ}\)C). In the UV/PS process, aromatics and TOC removals were influenced by the initial pH as demonstrated in (Figure 4a,b). The highest efficiency is obtained at an initial pH of 9 and 10. The results suggested that the alkaline conditions were more favorable than neutral and acidic conditions during the degradation of TA. A similar finding was reported in other studies relevant to these observations [57; 58; 59]. An increase of pH from three to nine, the photo-degradation efficiency of TA at 120 min irradiation increased from 80.78 to 96.38% and from 22.55 to 54.41%, respectively, for aromatics removal and TOC removal. In contrast, the rise of pH higher than pH 9 does not have any significant influence on the kinetics and TOC removals. This indicates that the highest degradation and mineralization efficiencies of TA by the UV/PS process can be reached at pH nine. These results confirm that very strict conditions (strongly acidic or basic) are less favorable to complete mineralization of TA [57; 58; 59]. Thus, the photo-degradation of TA requires a big amount of persulfate radicals and it cannot be carried out at any pH value (see Figure 4b). This may be relative to the abundance of radicals and their nature in the aqueous medium. The literature indicates that increasing the pH increases the  
Figure 4: Influence of initial pH on the changes of: (**a**) aromatics removal, and (**b**) TOC removal, during the treatment of 0.1 mM TA by UV/PS and UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}^{2+}\) processes. Experimental conditions: (UV/PS: [K\({}_{2}\)S\({}_{2}\)O\({}_{8}\)] = 53.1 mM, pH = 3–10 and T = 25 \({}^{\circ}\)C; UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}^{2+}\): [H\({}_{2}\)O\({}_{2}\)] = 29.4 mM, [Fe\({}^{2+}\)] = 0.18 mM, pH = 3–10, and T = 25 \({}^{\circ}\)C). concentration of hydroxyl anions in basic medium [56; 60]. The pH effect on the TA photo-degradation by UV/persulfate can be explained by, firstly, base-activated persulfate favored the production of SO4\({}^{\bullet-}\) under alkaline condition. SO4\({}^{\bullet-}\) doubled, as demonstrated in Equation (1). Second, a high pH, sulfate radicals SO4\({}^{\bullet-}\) react with OH\({}^{-}\) or H\({}_{2}\)O to generate hydroxyl radicals HO\({}^{\bullet}\) (E\({}^{\circ}\) = 2.7 V) based on Equations (2) and (3) [29; 61; 62; 63]. Thus, HO\({}^{\bullet}\) is a more powerful oxidant than SO4\({}^{\bullet-}\). It should be observed that HO\({}^{\bullet}\) and sulfates radicals SO4\({}^{\bullet-}\) oxidize organic compounds mainly in three ways: (i) Hydrogen abstraction, (ii) addition and substitution of alkanes and aromatics, and (iii) electron transfer from carboxylate groups [64]. On the other hand, in acidic pH, SO4\({}^{\bullet-}\) is the predominant radical species in the UV/PS process [60; 65]. In our work, the lowest TOC removal efficiency (22%) was observed at pH = 3 after 120 min of treatment (Figure 4b).