## 2 Advanced Oxidation Processes
### Electrochemical Technologies  
Electrochemical methods are also part of advanced oxidation processes and are widely used for degradation of pollutants. The use of these technologies on an industrial scale can be difficult, due to high costs, since one of the most used anodes is the boron-doped diamond (BDD), which is a very expensive material. [PERSON] et al. [36] used photo-electrocatalysis for PP removal using TiO\({}_{2}\) nanotubes as a catalyst. At pH = 3, total removal was achieved in only 30 min. The authors also showed that the presence of WO\({}_{3}\) in TiO\({}_{2}\) nanotubes enhances the photo-activity by 20%. [PERSON] et al. [85] used electrochemical oxidation with BDD anode and achieved total EP removal in about 15 min for 200 \(\upmu\)g/L of EP and 30 min when 600 \(\upmu\)g/L was used as the initial concentration. [PERSON] et al. [111], [PERSON] et al. [112], and [PERSON] et al. [113] removed 100 mg/L of methylparaben using electrochemical oxidation with BDD [111; 112] and DSA-Cl\({}_{2}\)[113]. [PERSON] et al. [111] had 100% removal in 20 min for electrochemical oxidation and photo-electrocatalysis with UVC radiation, while photochemical degradation led to 20% removal in almost 500 min reaction. When 3 g/L of Na\({}_{2}\)SO\({}_{4}\) was used as an electrolyte solution, the efficiency decreased, since total removal was achieved for photo-electrocatalysis in about 240 min, for electrocatalysis in 300 min, and the photochemical oxidation led to less than 10% in almost 500 min. This clearly shows the influence of electrolyte solution on the technology's performance. Moreover, it seems that NaCl presents a good behavior for these experiments. [PERSON] et al. [113] used 0.15 mol/L of NaCl as electrolyte solution, which also had 100% MP removal, but it was obtained in 40 min for electrocatalysis and photo-electrocatalysis, which did not show improvement when UVC radiation was added to the degradation process. UVC photolysis was also tested, but only 17% of MP was removed in 120 min. In the studies by [PERSON] et al. [111; 113], the presence of radiation was not able to increase the electrochemical experiments' efficiency, but when compared to single radiation, the high performance of the electrochemical route was noticed [113]. [PERSON] et al. [112] used BDD as an anode and 0.05 mol/L of K\({}_{2}\)SO\({}_{4}\) as an electrolyte solution but only achieved 34.65% of MP removal in 20 min for the best conditions. In fact, compared to the study of [PERSON] et al. [111], the choice of electrolyte solution may explain the difference in the obtained results. With this, it is possible to notice that NaCl and Na\({}_{2}\)SO\({}_{4}\) are good choices at a first sight, and the use of K\({}_{2}\)SO\({}_{4}\) should not be considered due to low performance. The removal of BuP by electrochemical technologies was also investigated. [PERSON] et al. [114] used electrochemical oxidation, using different materials as anode and stainless-steel as cathode, to remove 0.5 mg/L of BuP in an electrolyte solution of 0.1 M of Na\({}_{2}\)SO\({}_{4}\). BDD anode allowed a BuP removal of 100% in 15 min, while stainless steel and platinum only achieved 40% and 18% degradation, respectively. [PERSON] et al. [115] also removed BuP in river water with this technology, but using platinum or glassy carbon anodes, for different electrolyte solution (KCl, H\({}_{2}\)SO\({}_{4}\) and K\({}_{4}\)P\({}_{2}\)O\({}_{7}\)). In this condition, 95% of BuP was degraded in 180 min in the presence of 0.1 M of K\({}_{4}\)P\({}_{2}\)O\({}_{7}\) as electrolyte and 40 \(\upmu\)M of CTAC on glassy carbon. The study by [PERSON] et al. [114] proved the good performance of BDD over platinum and stainless-steel anodes. This should be expected, since one of the good characteristics of BDD is its good working performance, but the disadvantages such as its high cost can make it difficult to implement electrochemical experiments with this anode. Furthermore, the study of [PERSON] et al.