## 2 Centralized Treatment Plants
### Urban Wastewater Treatments
#### 2.1.1 UWW Disinfection
The solar photo-Fenton (SPF) process mediated by iron chelate Fe\({}^{3+}\) immunoisuccin acid (Fe:IDS) was evaluated on real secondary UWW effluent in a pilot plant raceway pond reactor (RPR) and compared with the Fe:EDDS SPF and sunlight/H\({}_{2}\)O\({}_{2}\) processes in inactivation of seven pathogens and degradation of ARGs. Regrowth tests (with and without catalase addition to discriminate a possible residual H\({}_{2}\)O\({}_{2}\) effect) were carried out. Fe:IDS SPF resulted in more effective pathogen inactivation due to a better combination of intra- and extracellular photo-Fenton mechanisms. The effect on ARGs was found to be ARG-dependent. Moreover, no relevant pathogen regrowth was observed, even in the absence of catalase, the real scenario. Fe:IDS SPF can be considered as an attractive solution for tertiary treatment in small wastewater treatment plants [49]. Similarly, a disinfection strategy based on Fe\({}^{3+}\)-NTA, H\({}_{2}\)O\({}_{2}\) and NaOCl has been set at quite real conditions by treating a WWTP secondary effluent, added with sulfuric acid, in an RPR. This novel approach operated in continuous flow mode and effectively reduced the _E. coli_, _Clostridium perfringens_ and MS2 coliphage, along with total coliforms (TCs) and _Enterococcus faecalis counts_. However, the EU 2020/741 thresholds for coliphage (\(\geq\)6 log-units) and _C. perfringens_ (\(\geq\)5 log-units) were not attained. The authors suppose that completely positive results can be obtained by increasing the NaOCl concentration and that this technology can address the challenge of disinfection at full-scale operation to produce water of B, C and D classes with no additional adjustments [50]. Four sulfate-based AOPs (SR-AOPs), obtained by the combination of peroxymonosulfate (PMS) with O\({}_{3}\) and H\({}_{2}\)O\({}_{2}\), were tested at the pilot scale to obtain simultaneously water disinfection and removal of CECs and ARGs. The PMS/UV-A, PMS/H\({}_{2}\)O\({}_{2}\)/UV-A (in two different molar ratios, 1:1 and 1:3) and PMS/O\({}_{3}\) treatments were carried out to produce remediated water for crop irrigation. The most effective treatment was the PMS/O\({}_{3}\) one, which was able to remove total aerobic microorganisms in 20 min and _E. coli_ in 5 min, to degrade 94% of CECs and remove six out of eight ARGs present in the WW. However, the remediated water was not suitable for reuse in agriculture, since it was phytotoxic, probably depending on the formation of substances such as bromate or nitrosamines. The PMS/H\({}_{2}\)O\({}_{2}\)/UV-A system, especially using a molar ratio of 1:3, resulted better than the PMS/UV-A in disinfection but not in CEC removal. Moreover, neither of these two systems was able to reduce the ARG content. In terms of operating costs, the PMS/O\({}_{3}\) system has the lowest cost (0.70 \(\upcelsm^{3}\)) due to the absence of UV-A radiation usage and to the shorter operating times. The system requires further improvements to reduce both its cost and phytotoxicity [51]. In spite of their simplicity and effectiveness in degrading recalcitrant chemical components, the Fenton and photo-Fenton processes are rarely employed at full scale. The review by [PERSON] et al. presents a critical analysis of the feasibility of these processes for full-scale diffusion, focusing on homogeneous processes and examining, in detail, the fundamentals, characteristics, process parameters, chemical and photochemical reactor designs and scale-up challenges. Examples of applications of these oxidative processes in pilot- and full-scale conditions are also presented [52]. For pottable reuse application of reclaimed water, the greatest risk is posed by viruses. An advanced water treatment train employing the novel SMART_plus_ (Sequential Managed Aquifer Recharge Technology, Berlin, Germany) biofilter was able to remove viruses when proposed and tested during a 3D pilot-scale study.