## 4 Discussion  
In this study, we investigated the performance of a self-assembled device to treat different kinds of wastewater by ozone injected into the water stream. O\({}_{3}\) dissolved in water has been used for sterilization and detoxification of fluids in all kinds of contexts [14; 45; 46; 47], rarely alone but usually as a pre or post treatment, according to the chemical/biological content and to the final use of the reclaimed water. Our aim was to test the possibility of employing our system both to treat small-moderate volumes of wastewater produced locally during various activities, such as agriculture, small industries, isolated communities, and to sanitize surface water or groundwater in areas where no potable water utilities are present, or they are temporarily not available because of some kind of emergency. Concerning the removal of chemical pollutants from WW, the experiments on a mixed solution of six representatives of the so-called micropollutants or emerging pollutants at high concentration like in industrial WW gave positive results. The system was able to completely degrade most of the parent molecules after 1 h of treatment and this duration would likely be shorter after future optimization. Only one compound retained more than 50% of its initial concentration. The effectiveness of experimental system in the degradation of organic pollutants was further confirmed by the comparison with similar, already published data [2; 31; 35; 48]. The COD and TOC values indicated that the overall organic content was not greatly changed after treatment, but the known role of ozone and its radicals is just to start the molecular degradation by oxidative attacks, enabling an easier biodegradation process, not to obtain extensive mineralization of the molecules [3; 49; 50]. To identify the degradation products was beyond our interest as several studies have been already published on the derivatives obtained by oxidation of various compounds included in our solution [2; 34; 51; 52]. Moreover, we aimed to replicate real cases of WW treatment, in which a detailed identification on all the compounds and their derivatives is usually not feasible, and the treatment's effects are evaluated by simple tests, the biotoxicological or microbiological ones. The evaluation of the treatment's effect on the micropollutants biotoxicity by the luminescent test was focused on the long-term results, since short-term assays can result in unrealistic data. As confirmed by data reported in Figure 4, the real toxicity of the untreated solution can be observed only in long-term measurements. The green algae response was also evaluated in long-term assays, to ensure the full expression of the pollutants' effects. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Samples**} & **CFU/100 mL** & **Regrowth** \\  & \(\pm\)**Uncertainty** & **CFU/100 mL** \\ \hline Untreated & 14,600 \(\pm\) 4000 & — \\ \hline O\({}_{3}\) treatment: 15 min & 1300 \(\pm\) 600 & 0 \\ \hline
30 min & 800 \(\pm\) 300 & 0 \\ \hline
60 min & 300 \(\pm\) 100 & 0 \\
120 min & 100 \(\pm\) 40 & 0 \\
240 min & 100 \(\pm\) 50 & 0 \\
360 min & 80 \(\pm\) 30 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The heterotrophic plate counts of freshly treated wastewater samples and of the same samples plated 7 days later. Regrowth phenomena did not occur, no colony was growing on plates of treated samples. The results can be considered consistent with those obtained from bacteria, even though the sensitivity of these organisms was different. The marine algae, which was more sensitive, did not grow at all, while the freshwater algae was able to grow, but only about the 20% the control did, without significant differences among the samples. These differences among the various test organisms are the rule and each research work will define a different order of sensitivity for the same organisms tested on different analytes [53].