## 3 Results
### The Photodegradation and Mineralization Profiles  
Of the samples withdrawn from the pesticide solution under treatment, we determined a decrease in both the active ingredient concentration and the degree of mineralization, expressed by the reduction in the ABS and in the TOC value, respectively.  
The amount of hydrogen peroxide added to the solutions (50 mL of H\({}_{2}\)O\({}_{2}\) at 30% solution) was selected according to our previous experience at the lab scale [33] and the literature data [21]. The pH values of the three solutions after hydrogen peroxide addition were in the range 7.4-7.6, and they were not modified, because this photodegradation procedure was intended for use at farms where a pH adjustment would be an unusual and unlikely operation. Furthermore, those values were suitable for performing the biotoxicity assays both before and after treatment.  
It was out of the scope of this work to follow the photodegradation mechanism by determining the kind and amount of the photoproducts, first of all because our main aim was to develop a more effective device by adapting the UV-H\({}_{2}\)O\({}_{2}\) AOP to the out-of-lab conditions encountered at farm locations. On the other hand, several studies on the photochemistry of the selected compounds were already available in the literature, as mentioned in the Introduction.  
Figure 3: The vacuum pump system employed to quickly and safely transfer the pesticide solution from the spray-tank, or any other container, to the photodegradation unit.  
Figure 2: The portable photolytic cell. From left to right: external aspect and dimensions of the system case, scheme of the UV lamps support, the support inside the case system. Below, a photo of the completed lamps’ support.  
In Figure 4, for each pesticide, the data obtained for the absorbance and the TOC parameters were reported in a double-axis graph in order to compare the trends of the two processes. Two hours was the first sampling interval chosen to evaluate the degradation. At that time, only the reduction in concentration of TBA and IMI and a modest IMI mineralization were measurable. Indeed, the AOPs proceed through complex pathways, starting with the fragmentation of the parental organic molecules, followed by various transformations leading, in optimal conditions, to the production of CO\({}_{2}\) and carbonates. The disappearance of the parent compound and the reduction of the organic molecule content can follow completely different kinetics.  
Concerning the selected pesticides, these differences were particularly evident for the compound TBA. This molecule, or better its degradation derivatives, resulted in being the most recalcitrant. TBA was degraded at 80% after about 6 h, but the TOC value of the solution was quite unaffected after 8 h of treatment (Figure 4a).  
Figure 4: The changes in both the active ingredient concentration and in the TOC content over time with respect to the untreated solutions (irradiation time 0). (**a**) TBA, (**b**) IMI, (**c**) AZO.  
A similar, and definitely less pronounced, discrepancy between the two processes was observed for the insecticide IMI; the parental molecule completely disappeared after 5 h of treatment, while to halve the TOC value, 7 h of irradiation was required (Figure 4b).  
On the opposite, the two phenomena showed the same trend in the case of AZO. The disappearance of the active ingredient was strictly followed by the reduction of the TOC value, both halved after 3 h of treatment. After this time, the two curves slightly diverged, probably because of the formation of resistant photoproducts (Figure 4c).  
The prototype was able to remove about 80% (mean value) of the active ingredients in an acceptable time (8 h), which can correspond, for example, to an overnight treatment. The mineralization rate was significantly lower, the mean value being about 44%, but it was known that to obtain the disappearance of any organic compound is a rather more difficult task.