#### 3.2.4 Mineralization and Toxicity Evaluation  
In order to investigate the degree of mineralization, TOC measurements were carried out during and at the end of the process. However, after 6 h of illumination less than 30% removal of the TOC was achieved indicating that recalcitrant intermediates are formed requiring more prolonged irradiation time for their elimination. Since the formation of various transformation products throughout treatment may pose environmental risks [59] the evaluation of the changes in toxicity during treatment is indispensable. In the present study a _Daphnia magna_ toxicity bioassay was applied to samples taken during the photocatalytic treatment and the immobilization of the organisms expressed as the % effect after 24 h and 48 h of exposure was determined. In Figure 11, the results from the bioassay are depicted. Obviously, photocatalytic treatment of the target mixture leads to a reduction in toxicity in general. After 2 h of treatment toxicity appears a reduction from 55% effect to 20% (48h) since most of the compounds of the mixture are by this time more than 70% degraded. However, after three hours of illumination a slight increase is depicted despite the fact that most of the parent compounds are more than 90% degraded, thus indicating the formation of by-products that may pose a slight toxic effect on the tested organism. After six hours of treatment, a 20% effect is still observed probably due to the presence of recalcitrant intermediates as it has been also indicated by the slight reduction of TOC (less than 30%). 2.5 Evaluation of the Photocatalytic Efficiency of the PLLA-GO-50 wt% TiO\({}_{2}\) Composite Film on the Photodegradation of the Mixture of Antibiotics in a Wastewater Matrix  
In order to examine the efficiency of the PLLA-GO-50 wt% TiO\({}_{2}\) composite film on the elimination of the target compounds being present in a wastewater matrix, experiments were conducted in a wastewater effluent obtained from an urban wastewater treatment plant. In Table 4, the physicochemical characteristics of the effluent are depicted. In Figure 12, the photocatalytic degradation of the antibiotic compounds is presented. Obviously, the newly synthesized PLLA-GO-50 wt% TiO\({}_{2}\) composite film is effective enough to cause more than 90% degradation for most of the studied compounds. In Table 5, all kinetic parameters are presented. Figure 11: Changes in toxicity of the treated solution during photocatalytic treatment with PLLA–GO–50 wt% TiO\({}_{2}\). C\({}_{0(\text{drug})}\) = 1 mgL\({}^{-1}\), PLLA–GO– TiO\({}_{2}\) = 1 gL\({}^{-1}\), I = 750 Wm\({}^{2}\). \begin{table}
\begin{tabular}{c c} \hline \hline
**Physicochemical Parameters** & **Values** \\ \hline BOD (mgL\({}^{-1}\)) & 11 \\ COD (mgL\({}^{-1}\)) & 59 \\ SS (mgL\({}^{-1}\)) & 8.4 \\ N-NH\({}_{3}\) (mgL\({}^{-1}\)) & 9.3 \\ N-NO\({}_{3}\) (mgL\({}^{-1}\)) & 1.5 \\ P\({}_{\rm tot}\) (mgL\({}^{-1}\)) & 1.2 \\ Bicarbonate (mgL\({}^{-1}\)) & 380 \\ Chloride (mg\({}^{-1}\)) & 124 \\ TOC (mgL\({}^{-1}\)) & 14.3 \\ pH & 7.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physisochemical characteristics of the wastewater effluent. Figure 12: Photocatalytic degradation of the antibiotics mixture in the presence of PLLA–GO–50 wt% TiO\({}_{2}\) composite films in a wastewater effluent (C\({}_{0(\rm drug)}\) = 1 mgL\({}^{-1}\), PLLA–GO–50 wt% TiO\({}_{2}\) = 1 gL\({}^{-1}\), I = 750 Wm\({}^{2}\)).