## 3 Results
### Energetic Considerations  
An indicator of energy efficiency of a process is represented by the \"electrical energy per order\" (EEO), which has been defined as the amount of kWh's required to reduce a pollutants' concentration by one order of magnitude (i.e., on _log_ or 90%) in 1 m\({}^{3}\) of solution [36]. EEO values are thus expressed as kWh m\({}^{-3}\)order\({}^{-1}\) (also indicated as kWh m\({}^{-3}\)log\({}^{-1}\)), and are used to compare technologies for a given degradation reaction, even if based on published reports and articles from different periods, independently of actual energy prices. Depending on process type, pollutant and its initial concentration, reported EEO values range between 0.6 to above 300. The more efficient the process in the removal of a pollutant, the lower will be the calculated EEO value, however this value can be affected also by the specific composition of the water matrix, hence it may be different for the same contaminant in different conditions. As shown in Figure 5[36] EEO values for the same compound may vary substantially between pure (monocomponent) and complex (multicomponent) solutions. In case of ozonation, for example, variability could be explained by water matrix interference on radical formation: radical scavenging and water matrix composition could directly affect generation and interaction of radicals, hence application of the EEO index to compare of experimental results obtained from different solution matrices is not recommended. An important caveat of EEO is that it evaluates an entire system, hence all aspects of reactor and reaction are expressed in a single metric. Another important one is that EEO does not take into account the cost or efficiency of obtaining reagents. However, properly determined EEO values, in addition to allow quick and simple technology comparison, may provide information for processes scale-up, as well as for sustainability analysis [37]. Given the above caveats, EEO should only be determined for processes that are already optimized, and demand for auxiliary external oxidants should be included in the EEO estimation by considering any additives as \"stored electric energy\", however, the majority of studies are limited to considering the electricity used directly in the process. For example, a Fenton reaction's unique power requirement is for solution stirring, however, it requires peroxide addition to occur, but EEO is not able to reflect the costs (certainly not the monetary cost, and perhaps--depending on methodology- not even the energetic-equivalent) of peroxide dosing necessary to operate it. In order to make some comparisons among processes, some examples are reported below. Degradation of a mix of micropollutants (atrazine, NDMA, MTBE, dioxane, bisphenol A, microcystine, diclofenac, ibuprofen) by UV/H\({}_{2}\)O\({}_{2}\) from supply water in a Dutch water treatment plant showed, under optimized conditions, EEOs in the range 1.08--2.84 [38]. In that case, only 8-14% of the energy input could be attributed to electrochemical production of H\({}_{2}\)O\({}_{2}\), while the rest is required to operate the low pressure UV lamps. Compounds with lower reaction rates with -OH, or not responding to photolysis, would register higher EEOs at similar treatment levels. Other researchers reported, for a similar process, EEO values of 0.17 for diclofenac removal, and of 0.62 for Carbamazepine removal [39].