## 3 Results and Discussion
### UV/H\({}_{2}\)O\({}_{2}\)-SSHFCW System  
The synthetic CropWW initial concentration (C\({}_{0}\)), for configurations of the hybrid system, was 41.8 mg/L of malathion and 22 mg/L of TOC. In this section, the only difference between the three UV/H\({}_{2}\)O\({}_{2}\)-CW systems evaluated was the HRT in the CW, as it was described in Section 2.3. Figure 8 shows the removal rates in the UV/H\({}_{2}\)O\({}_{2}\)-CW systems. \begin{table}
\begin{tabular}{c c c c c} \hline
**Pretreatment Option** & **Irradiation Time, Min** & **Hydrogen Peroxide, mM** & **TOC Removal, \%** & **Malathion Removal, \%** \\ \hline
1 & 75 & 49 & 30–40 & 70–80 \\
2 & 90 & 57 & 40–50 & 70–80 \\
3 & 90 & 65 & 50–60 & 90–100 \\
4 & 120 & 65 & 50–60 & 90–100 \\ \hline \end{tabular}
\end{table} 
Table 2: Potential combinations of irradiation time and H\({}_{2}\)O\({}_{2}\) dose during the pretreatment operation, considering both malathion and TOC removal. Note: This table is modified from the result of the response surface design analysis, where the confidence intervals are bilateral to estimate the effect of higher and lower levels. Figure 8: TOC behavior dosage during malathion removal in hybrid UV/H\({}_{2}\)O\({}_{2}\)-CW system at three hydraulic retention times used for the CW stage. The values represent the mean values of three replicates. Ce = TOC concentration at time t (operation days), C\({}_{0}\) = initial TOC concentration (the value corresponds to the AOP effluent). Figure 7: Effect of the combination of H\({}_{2}\)O\({}_{2}\) doses and different UV irradiation times over the concentration of **(a)** TOC and **(b)** malathion. The dotted line box indicates the region with high removal but takes into consideration the shortest possible irradiation times and peroxides dosage. Malathion removal in the hybrid system was \(94.7\pm 4\), \(97.9\pm 2\) and \(98.3\pm 3\%\) for the wetland HRTs of 1, 2 and 3 days, respectively. Although higher pesticide removal was observed at longer HRT in CW, there was not significant difference (\(p=1.2\)), since removal mainly occurred in the AOP pretreatment which was the same for all three systems. In fact, this pretreatment achieved between 95% and 100% of malathion removal with the operational parameters selected. Regarding TOC, the three CW configurations coupled to UV/H\({}_{2}\)O\({}_{2}\) pretreatment achieved \(65\pm 8.3\%\) TOC removal at 17 operation days, which is 15% more than the AOP as the unique treatment. The results obtained suggest that a portion of malathion by-products, generated during the AOP, were removed in CW by some mechanism other than biodegradation, since HRT would influence the removal efficiency in biological systems (time contact microorganisms-contaminant). Some authors have reported that particles or surfaces of organic-inorganic nature can adsorb organic persistent molecules such as pesticides, drugs and their cyclic byproducts by Van Der Waals forces and/or physisorption, as occurs in soils and sediments [42; 43]. In CWs, sorption processes can occur in support media, due to occluded and interstitial porosity. In addition, sorption also occurs on hydroxyalkanoates and hydroxybutyrateates, main compounds of microbial biofilm [44; 45] and onto the root exudates of vegetation rhizomes [44; 46]. Regarding TOC removal, the performance of the UV/H\({}_{2}\)O\({}_{2}\)-CW operated with 1 d HRT was significantly lower than the other two systems (\(p=0.0015\)), which is mainly because the recommended HRT for CW range from 1.5 to 4 days. In fact, in a non-aerated attached-biomass reactor, catabolic processes are not observed before one day HRT [18; 47]. Furthermore, this hybrid system did not show any trend throughout the experiment (Figure 8), so it is likely that the removal achieved in the CW was due to sorption and biosorption. The UV/H\({}_{2}\)O\({}_{2}\)-CW operated with 2 and 3 d HRT have no significant differences between removals (\(p=0.2\)).