## 2 Results and Discussion
### Removal of the Mixture of Different Classes of Pollutants in Actual Water  
In order to get experimental conditions closer to real ones, tests were carried out using a mixture of all the contaminants previously assessed individually, maintaining similar concentrations. The comparison of the performances of the photocatalysts is reported in Figure 4. Additionally, in this instance mercury removal could only be achieved through the use of ZnO-based materials but, in contrast to the results obtained in the single tests, ZnO showed a lower effectiveness than the two modified materials. As regards CECs, the comparison between the photocatalysts yielded similar results to those obtained with the single pollutants, except for diclofenac for which P25 proved to be much more effective. Overall, the better performance for the contaminants' removal was obtained with ZCC, especially towards the odorous molecules, attaining the abatement of all pollutants within 1 h. The analysis of the kinetic constants calculated for ZCC revealed that the removal rate of Hg(II) and CECs in the mixture was even higher than that obtained for solutions with the single contaminants (see Table 1). Figure 3: Degradation profiles of geosmin and MIB obtained using synthesized materials and the benchmark P25. It is noteworthy that the experiments for mercury removal performed on the single metal required the stripping with nitrogen of the solution with the aim of removing oxygen that might compete with the Hg(II) species for the photogenerated electrons. As a matter of fact, when the same test was repeated without stripping, the photocatalytic performance was clearly worse (Figure 5). However, when irradiation was carried out on the mixture of pollutants without nitrogen purging, it was observed at a faster removal of mercury than in the reductive atmosphere. This is likely caused by the lower charge recombination that takes place in the presence of the CECs and odorous molecules, since photogenerated holes should be involved in the oxidation process of the organic molecules while the electrons in the reduction of mercury. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Matrix** & **Composition** & & & & **k [min –1]** & & & \\ \hline  & & **BTA** & **SMZ** & **BPA** & **DIC** & **Hg(II)** & **MIB** & **Geosmin** \\ \hline Milli-Q water & Single class & 0.22 & 0.09 & 0.05 & 0.13 & 0.07 & 1.68 & 0.80 \\ \hline Milli-Q water & Mixture & 0.32 & 0.13 & 0.07 & 0.13 & 0.10 & 0.06 & 0.11 \\ \hline Aquaculture & Single class & 0.17 & 0.05 & 0.04 & 0.05 & 0.11 & 0.06 & 0.09 \\ \hline Aquaculture & Mixture & 0.20 & 0.06 & 0.04 & 0.07 & 0.10 & 0.05 & 0.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between the kinetic constants obtained with the ZCC photocatalyst for the removal of the evaluated pollutants, individually and in a mixture of them in two different matrices: Milli-Q and real aquaculture water. Figure 4: Comparison of photocatalytic mercury removal profiles (**a**) and pseudo-first order calculated kinetic constants of CECs degradation (**b**) and MIB and geosmin degradation (**c**) with the different photocatalysts in the mixture of pollutants. The removal of the Total Organic Carbon (TOC) was monitored along the reaction performed with the mixture of the three classes of pollutants in Milli-Q water following a longer irradiation time for attaining the organics degradation. The results are reported in Figure 6.  
The complete removal of the initial contaminants was accomplished in 60 min while, as expected, more time was needed to attain the complete mineralization in the mixture of compounds. Nevertheless, after only 1 h a 60% decrease in initial TOC was obtained using the two doped photocatalysts (ZC and ZCC) whereas a 40% reduction was achieved with the pristine ZnO and the benchmark P25, hence indicating the presence of a higher amount of remaining degradation by-products.