## 4 Discussion  
This review paper provides a comparative summary of innovative, emerging AORPs (EB and NTP) versus currently adopted AOPs. To facilitate process efficiency comparison, data concerning reported EEO values for each technology were gathered from the analysis of literature articles. The EEO concept provides an initial parameter that may help to directly evaluate and compare AOPs based on energy efficiency, notwithstanding strong limitations to its use linked to the variability of all influencing factors in its determination. Despite a high dispersion of reported data, a significant trend of difference among AOPs' efficiency, as measured by EEO, could be observed. Regarding economic considerations alone, referred to EEO values, radiolysis appears to be the most suitable technique [41]. Considering traditional AOPs, EEO values for UV/H\({}_{2}\)O\({}_{2}\) are much lower than those for UV and photocatalysis; at the same time, UV techniques have generally higher energy consumption, and are less efficient in elimination of degradation by-products. Although EB and NTP applications achieved comparable or better efficiencies to those of UV/H\({}_{2}\)O\({}_{2}\), the best practical alternative for a particular situation will depend mainly on reliability, robustness and cost. Radiation-based treatment technology by EB generally represents a potential, environmentally friendly alternative to traditional AOPs, without use of chemicals, minimal by-products generation and absence of DBPs in water disinfection (in conventional chlorination, toxic organo-chlorine products, mutagenic and carcinogenic, may occur). Because of simultaneous generation of oxidizing and reducing radicals, ionizing radiation methods are recognized as some of the most versatile AORPs, able to degrade a wide variety of pollutant in solution, with the technical possibility of achieving complete mineralization. EB technology has also shown higher radical-generating efficiency than ozone-based processes. Their efficiency could be further substantially increased, reducing input energy requirements, by combining them with different catalysts or biological processes in hybrid AORPs processes. Although there are many successful pilot-scale literature reports of radiolytic technologies, these have been tested on full-scale, long running applications only in a few reported instances. NTP technology has only very recently been tested for treatment of contaminants in solution, and even with several reported success experimental applications, and demonstrated low energy requirements, it is still regarded as a niche field. Recent studies showed efficacy of NTP in PPCPs and EDCs (trichloroethylene-TCE, N-nitrosodimethylamine-NDMA, 1,4-dioxane, and methyl _tert_-butyl ether-MTBE) degradation in pilot batch experiments [25]. Currently, NTP technology has still limited commercial availability and has not been tested in full-scale settings, so its long-term performance is still undetermined. In addition, its application is currently limited to low-flow setups, due to its thin-film configuration constraints. In reported literature, studies concerning all types of AOPs are most often conducted with high-purity laboratory-spiked solutions, representing very different situations from the real world, in which wastewater, grey water, and even tap water will contain a variety of ions, minerals, and organic \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**m3/day Treated** & **Electron Beam** & **Ozone** & **UV** & **Chlorine** \\ \hline
10,000 & 0.29 & 0.25 & 0.17 & 0.013 \\
50,000 & 0.073 & 0.086 & 0.171 & 0.013 \\
100,000 & 0.050 & 0.064 & 0.054 & 0.013 \\
200,000 & 0.041 & 0.053 & 0.047 & 0.013 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Estimated costs comparison for disinfection of sewage water (2010 US $/m3). compounds.