## 3 Applications and Limits of ATPs in Water and Wastewater Treatment
### ATP Efficiency Enhancement and Process Combination  
While conventional AOPs and ARPs rely heavily on chemicals or catalysts for the generation of reaction-driving radicals, radiolysis-based AORPs do not necessarily require such additions, due to the high intensity of the energy transfer occurring in these processes. However, even their efficiency may be further increased by appropriate process management, with possible synergetic effects of irradiation and the addition of nanoparticles (NPs) of various nature on solutes' decomposition, enhancing radical production and the reaction yield [81]. Most ATPs' performance may be enhanced by the application of advanced materials of different nature and/or NPs, including semiconductors, nanoclays, nanocatalysts, nanoclusters, nanorods, and nanocomposites. Nanotechnology consists of the manipulation of materials, including TiO\({}_{2}\), palladium, Fe\({}_{3}\)O\({}_{4}\), cerium oxide, graphene oxides, magnetic chitosan, and others, at a scale of \(<\)100 nm, taking advantage of unique phenomena that may occur realized at that size scale due to their high surface area to volume ratios, greatly improving adsorption properties. Research recently addressed wastewater treatment also with the use of complex nanocomposites, such as \begin{table}
\begin{tabular}{l l l} \hline \hline \multicolumn{1}{c}{**Contaminant**} & \multicolumn{1}{c}{**Type of Process**} & \multicolumn{1}{c}{**Remarks/Results**} \\ \hline \multicolumn{3}{c}{_Pesticides_} \\ \hline Diazinon & \(\gamma\)-irradiation & Complete degradation at \\  & & irradiation of 6 kGy, reduction at \\  & & drinking water MRL at 1.5 kGy \\ PCB & \(\gamma\)-irradiation & 96\% degradation at \(<\) 0.1 kGy \\ Procloraz, Imidacoprid, & EB & 99\% removal at 5 kGy \\ Carbotofuran, Dimetoato & & \\ \hline \hline \multicolumn{3}{c}{_Other pollutants_} \\ \hline Perchlorate & EB & 30–40\% removal at \(<\)5 kGy \\ Trihalomethanes & \(\gamma\)-irradiationEB & 87–95\% removal at 2–6 kGy \\  & & Up to 99.9\% removal at \(<\) 5 kGy \\ DBPs & & Up to 68\% removal at \(<\) 5 kGy \\ MTBE & EB & Up to 88\% removal at \(<\) 5 kGy \\ NDMA & EB & Up to 88\% removal at \(<\) 5 kGy \\ \hline \hline \end{tabular}
\end{table} 
Table 8: _Cont._Co\({}_{x}\)Fe\({}_{3-x}\)O\({}_{4}\), CoFe\({}_{2}\)O\({}_{4}\) magnetic nanoparticles, and bismuth silver oxide [82]. Polymeric dendrimers are randomly hyper-branched polymers consisting of spherical macromolecules with a dense shell morphology between 2 and 20 nm size. They are very efficient adsorbents for the removal of toxic metal ions, radionuclide, and organic solutes from water [83]. Metal/metal oxide nanoparticles, including silver, gold, and palladium, have also been widely investigated for wastewater treatment: Noble metal-structured photocatalysts can significantly improve the photoactivity of the semiconductor NPs, depending on the substrate to be degraded [84]. Nanosized silver showed strong antimicrobial properties; gold-impregnated palladium NPs have been used to destroy TCE from groundwater, with a 2200 times better performance than palladium catalyst alone; other metal oxide nanoparticles, such as TiO\({}_{2}\), ZnO, and CeO\({}_{2}\), have demonstrated a capacity for the degradation of organic pollutants in solutions [82]. Carbon-based nanomaterials, such as fullerenes, carbon nanotubes (CNTs), nanosize diamonds and nanosize wires, graphene oxide [85], and chitosan [86], have been used as sorbents for organic compounds in aqueous solutions. In particular, graphene, a two-dimensional recently identified form of carbon, is the thinnest and the strongest material ever measured, and has received much attention in various scientific applications due to its chemical stability, higher mobility as a charge carrier, and large surface area.