| Disinfectant | Description |
| Chlorine | For Cl2-founded ED, fresh tendencies were noted to substitute pressurized Cl2 with chlorine containing solutions formed via electrochemical technology [75] [76] [77] , frequently running at Cl− < 1 g/L. Chlorine species mixture could include dissolved chlorine (Cl2,dis), hypochlorous acid (HOCl), and hypochlorite ions (OCl−) jointly known as free active chlorine. Inorganic chloramines may be included in the bonded active chlorine and are viewed as undesirable by-products, as well as organic chloramines [78] [79] [80] . The simple and cost-effective anodic production, storability, and long-term residual effect interpret the excellent significance of Cl2-founded disinfection until now [81] . The technology is common and mostly employed in potable water disinfection, swimming pool water and seawater treatment [82] [83] . Supplementary disinfecting power may be attributed to another component, dichlorine monoxide (Cl2O) [84] , even if additional investigation remains required. |
| Chlorine dioxide (ClO2) | The progressive replacement of Cl2 as a disinfectant is more and more pronounced [85] [86] [87] . Chlorine dioxide (ClO2) forming fewer by-products and odor has been adopted in such approach [77] . Electrochemically, ClO2 could be formed onsite using undivided electrochemical or divided 2- or 3-compartment cells by anodic chlorite oxidation or cathodic chlorate reduction, ore from both processes [33] [88] [89] . At the commercial level, small cells having ion-exchange membranes have been proposed. The starting chlorite solution is in the domain of g/L concentration. ClO2 is formed in the g/h domain with performances bigger than 80% at pH 4 - 6. Bergmann [33] suggested two procedures of generating ClO2 for surface disinfection via adding scavengers to the chlorite solution at mg/L level domain. Under regulated parameters, total efficiencies could be attained in undivided cells [33] . For instance, when a chlorite solution is mixed with ozone solutions (formed electrochemically or by silent discharge) [90] , a defined molar ratio exists, conducting to nearly complete chlorite-to-chlorine dioxide conversion (Figure 3). In such situation, a scavenger avoids secondary reactions of the intermediate . |
| Ozone (O3) | It was ultramodern to generate ozone (O3) on PbO2, Platinum, SnO2, and other anodes [91] [92] . Recent Boron Doped Diamond (BDD) anodes in divided cells are more performant, furnishing O3 at bigger levels and formation rates of 10−4 - 10−3 g/h∙cm2 [93] . The credible onsite analysis of single oxidants inside a combination of O3 and different oxidants stays an unsolved difficulty. |
| Hydrogen peroxide (H2O2) | Methods employing oxygen-reducing cathodes could lead to ~2% (weight) H2O2: O2 + 2H+ + 2e− → H2O2 (5) This is much more juxtaposed to the anodic formation of two hydroxyl radicals on noncatalytic BDD pursued by their reaction to H2O2. Reaction between OCl− and H2O2 could lead to singlet and triplet oxygen production [94] . |
| Others | Additional disinfectants and technologies may be noted such as peroxodisulfate [95] [96] , chloramination [97] , bromine, and ferrates [35] [39] [71] even if without large industrial use. |