## 3 Results and Discussion
### Influence of Hydrogen Peroxide and Ferrous Iron Concentrations  
The amount of hydrogen peroxide and ferrous ions are the main factors affecting the cost of the operation and the process efficiency for many wastewater treatment facilities by Fenton and phot-Fenton processes [73; 74]. Photo-Fenton process efficiency can be assessed readily in terms of both the absolute concentration of reagents (hydrogen peroxide and ferrous ions) and the weight ratio ([H\({}_{2}\)O\({}_{2}\)]/[Fe\({}^{2+}\)]). Several researches affirm that the performance of photo-Fenton process to degrade organic matter present in water is mainly related to the production of hydroxyl radicals by chemical and photochemical decomposition of hydrogen peroxide [41; 43]. For this subject, some experiments were conducted at different initial oxidant concentrations using 0.1 mM TA at optimum pH 3 and at a room temperature of 25 \({}^{\circ}\)C. Ferrous iron concentration and hydrogen peroxide concentration were examined in the range of 0-0.27 mM and 14.7-58.8 mM, respectively, for TA degradation. Figures 6 and 7 show the effect of ferrous iron and hydrogen peroxide concentrations on aromatics and TOC removals during the treatment of TA by photo-Fenton process. As it can be observed in Figures 6a and 7a, aromatics removal during the treatment of TA does not depend on the initial contents of ferrous ions and hydrogen peroxide. There is no effect on both the kinetic and the efficiency of absorbance percentage removal. Indeed, over 94% of absorbance reduction was reached in any concentration of ferrous ions and hydrogen peroxide. Thus, it can be concluded that a total disappearance of TA was obtained with the addition of ferrous ions and hydrogen peroxide within the first 60 min of treatment by photo-Fenton process. However, without the addition of a catalyst, 69.42% of absorbance removal could be achieved in UV/H\({}_{2}\)O\({}_{2}\) process after 6 h of treatment (Figure 6a). It should be noted that a partial mineralization was obtained under these experimental conditions. These results indicate that ferrous ions are excellent catalysts and a small catalytic amount may be sufficient to decompose H\({}_{2}\)O\({}_{2}\) efficiently into hydroxyl radicals HO\({}^{\bullet}\). That is why the H\({}_{2}\)O\({}_{2}\) concentration is higher than Fe\({}^{2+}\) in all the experiments. In contrast, Figures 6b and 7b show that the ferrous iron and hydrogen peroxide concentrations have an important effect on the rate of TOC removal during the photo-Fenton treatment. In fact, the incorporation of Fe\({}^{2+}\) enhanced the efficiency of UV/H\({}_{2}\)O\({}_{2}\) for TA degradation (see Figure 6b). It is noticed that, in the presence of Fe\({}^{2+}\) catalyst, the degradation efficiency is more than 80% after 120 min treatment, while in the absence of Fe\({}^{2+}\) catalyst, the efficiency of the organic compounds degradation is less than 58% for 420 min of reaction time. Thus, the absence of ferrous iron during the mineralization of TA resulted in the latter's slow degradation. This could be due to the retarding production of excessive generated reactive radicals. Figure 5: Effect of persulfate dose on the changes with time of: (**a**) Aromatics removal, and (**b**) TOC removal by UV/PS process. Experimental conditions: [TA] = 0.1 mM; [PS] = 17.70–70.80 mM; T = 25 \({}^{\circ}\)C; and pH = 9. However, by adding ferrous iron, the TOC removal increases from 80.15 to 94.27% after increasing the Fe\({}^{2+}\) dose from 0.09 mM to 0.18 mM, and then it remains constant above this latter concentration. Moreover, the kinetic of TOC removal decreases to a dose of 0.27 mM. Hence, an almost complete conversion of TA was achieved after 120 min of the treatment of TA by photo-Fenton process for 0.18 mM of ferrous iron. These results can be interpreted by the fact that the addition of low amounts of ferrous iron (0.09 mM) does not enhance the performance of photo-Fenton process in wastewater treatment.