# Optimization of Organic Content Removal from Aqueous Solutions by Fenton-Ozonation
## 3 Results
### Fenton-Pervzone Process  
In order to achieve complete mineralization of 2,4-D, the Fenton process is coupled with ozonation. For this purpose, the experimental setup shown in Figure 1 was used. Briefly, the ozone concentration was fixed at 25 g\(\cdot\)Nm\({}^{-3}\)[26]. The treated solution had a volume of 500 mL, with an L27-Fe dose of 730 mg\(\cdot\)L\({}^{-1}\) and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) at 224 mg\(\cdot\)L\({}^{-1}\), corresponding to the operating conditions of run 13 (Table 2). This experiment was the only one to achieve complete degradation of 2,4-D (Y\({}^{60 min}_{HPLC}=100\%\)), although the mineralization remained limited to 59%. The degradation of 2,4-D by the Fenton-peroxone coupling was monitored over time by HPLC (Figure 7a), while mineralization was assessed by TOC analysis (Figure 7c). Lastly, the apparent degradation kinetics were modeled using a pseudo-first-order kinetic model (Figure 7b). To assess the impact of this coupling (O\({}_{3}+\)H\({}_{2}\)O\({}_{2}\)) as well as the presence of iron on the carbon surface, the degradation of 2,4-D was systematically compared to that obtained by ozonation alone (O\({}_{3}\)), peroxonation (O\({}_{3}+\)H\({}_{2}\)O\({}_{2}\)), and their combinations with either L27 or L27-Fe. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & **Parameters** & & **Response** & \\ \cline{3-8}  & **Objective** & **Criteria** & **Fe-L27 Dose,** & **H\({}_{2}\)O\({}_{2}\) Dose,** & **Solution pH,** & **Y\({}^{60 min}_{ TOC}\)** & **Desirability** \\  & & & **mg/L** & **mg/L** & \(-\) & **\%** & \\ \hline
1 & & x\({}_{1}\), x\({}_{2}\) and x\({}_{3}\) in range & 730 & 224 & 2.98 & 78.5 & 1.0 \\
2 & max (Y \({}^{60 min}_{ TOC}\)) & x\({}_{1}\), x\({}_{2}\) in range, x\({}_{3}\) = 0 & 746 & 26.8 & 5.5 & 45.4 & 0.8 \\
3 & & x\({}_{1}\), x\({}_{2}\) in range, x\({}_{3}\) = 1.732 & 746 & 26.8 & 8.1 & 49.3 & 0.842 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Summary of the main model indicators. Figure 6: Dependence of apparent constant rate of the Fenton process on the H\({}_{2}\)O\({}_{2}\) dose according to HPLC and TOC analyses. Figure 7a shows that, for all tested processes, 2,4-D degradation occurs relatively quickly, with degradation rates ranging from 69% to 100% within the first 10 min of treatment. The system combining Fe-L27, O\({}_{3}\), and H\({}_{2}\)O\({}_{2}\) demonstrates the highest efficiency, achieving complete degradation within 10 min (Table 8). In contrast, ozonation alone (O\({}_{3}\)) is the least effective because it relies on the direct action of ozone, with less generation of hydroxyl radicals or catalytic activation. In contrast, the combined processes enhance oxidation through multiple pathways, making them much more efficient. Several studies have reported similar findings when comparing the degradation of 2,4-D by ozonation and by other ozone-based combined processes. (O\({}_{3}\)/plasma, O\({}_{3}\)/Fe\({}^{2+}\), O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\)) [32; 33; 34; 35]. The addition of hydrogen peroxide and activated carbon significantly enhances 2,4-D degradation, suggesting a synergistic effect leading to a greater production of free radicals that drive the degradation of the molecule. The kinetic modeling curves (Figure 7b) fit the experimental data well (R\({}^{2}\) values ranging from 0.96 to 0.99), confirming that the degradation follows a pseudo-first-order kinetic model as shown by various authors who have worked on pollutant degradation using advanced oxidation processes (AOPs) [32; 36; 37; 38]. Figure 7: **(a)** Degradation rate kinetics of 2,4-D monitored by HPLC. **(b)** Kinetic modeling of 2,4-D degradation according to the pseudo-first-order model. **(c)** Mineralization rate kinetics of 2,4-D. **(d)** Mineralization rate of 2,4-D as a function of the applied processes.