# Electrodegradation of Selected Water Contaminants: Efficacy and Transformation Products
## 3 Results and Discussion
### Removal Efficiency, Kinetic Analysis, and Energy Consumption of Electrooxidative Treatment
#### 3.2.2 Kinetic Analysis of EO Treatment  
In this study, the kinetics of the EO of t-OPPE, t-OP, and DBP were studied using reaction models by analysing the kinetic data obtained from the EO experiments. The following parameters were derived from the applied kinetic models: the rate constant (\(k\)), coefficient of determination (\(R^{2}\)), and half-life (\(t_{1/2}\)). These parameters were calculated based on the experimental data, allowing for an accurate assessment of the reaction kinetics under different treatment conditions. The best-fitting model was determined based on the coefficient of determination (Table 2). The kinetics of the EO of t-OPPE follow first-order reaction kinetics, as confirmed by the simulation plot (Figure 4a), which shows a strong alignment of the first-order model with the experimental data. In contrast, the EO of DBP in H\({}_{2}\)SO\({}_{4}\), using both first-order and second-order reaction models, confirmed that the reaction follows second-order kinetics (Figure 4b). The same approach was applied to other treatments (Supplementary Materials S2 Kinetics, Figures S2a-c). The high degradation rate observed in sulphuric acid medium suggests the in situ electrochemical generation of S\({}_{2}\)Os\({}^{2-}\), followed by its activation to sulphate radicals (SO\({}_{4}\)\({}^{2-\bullet}\)), which drive the oxidation of DBP through a radical-mediated pathway. This interpretation is supported by literature describing the electrochemical production of persulphate under acidic conditions and its role as a precursor of sulphate radicals with high oxidative capacity (\(E^{\circ}\) = 2.6-3.1 V) [46]. The radical scavenger test confirmed the role of the radical-mediated pathway (Supplementary Materials S3 Radical scavenger test). Comparable degradation efficiencies in Na\({}_{2}\)SO\({}_{4}\) and H\({}_{2}\)SO\({}_{4}\) suggest only a slight enhancement under acidic conditions, supporting literature-based assumptions on pH influence and aligning with our previous findings [40]. The present study's kinetic findings align well with the insights reported by [PERSON] et al. [47], who emphasized that sulphate radicals (SO\({}_{4}\)\({}^{2-\bullet}\)) exhibit substrate-specific reactivity and follow mechanisms such as electron abstraction, addition-elimination, and decarboxylation, particularly effective under acidic conditions. This supports the rapid DBP degradation observed in our study with the H\({}_{2}\)SO\({}_{4}\) electrolyte (\(t_{1/2}\) = 8.46 min, \(R^{2}\) = 0.999). Similarly, [PERSON] et al. [48] demonstrated that SO\({}_{4}\)\({}^{2-\bullet}\) and OH\({}^{\bullet}\) were the dominant oxidants at pH 3.0 and 7.0 in a persulphate/zero-valent iron system, with a significant inhibition of DBP degradation kinetics upon the addition of radical scavengers, confirming the radical-driven pathway [48]. While [PERSON] and [PERSON] [49] did not provide specific kinetic constants, their review highlighted sulphate radical-based advanced oxidation processes as among \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Substance**} & **Supporting** & **Reaction** & **Rate Constant** & \multirow{2}{*}{**Unit of _k_**} & \multirow{2}{*}{**\(\mathbf{R^{2}}\)**} & **Half-Life** \\  & **Electrolyte** & **Order** & & **(k)** & & **(t\({}_{1/2}\), min)** \\ \hline t-OPPE & Na\({}_{2}\)SO\({}_{4}\) & First & 0.07530 & min\({}^{-1}\) & 0.9892 & 9.21 \\ t-OP & Na\({}_{2}\)SO\({}_{4}\) & First & 0.06570 & min\({}^{-1}\) & 0.9788 & 10.55 \\ DBP & NaCl & Second & 0.00527 & mg\({}^{-1}\).min\({}^{-1}\) & 0.997 & 38.69 \\ DBP & Na\({}_{2}\)SO\({}_{4}\) & Second & 0.01650 & mg\({}^{-1}\).min\({}^{-1}\) & 0.955 & 12.82 \\ DBP & H\({}_{2}\)SO\({}_{4}\) & Second & 0.02170 & mg\({}^{-1}\).min\({}^{-1}\) & 0.999 & 8.46 \\ \hline \end{tabular}
\end{table} 
Table 2: Kinetic parameters of EO of t-OPPE, t-OP, and DBP in different supporting electrolytes. Figure 4: (**a**) Comparison of experimental data with first- and second-order kinetic models for t-OPPE degradation.