To produce hydrogen (H
2) and oxygen (O
2), electrolytic water splitting (EWS) emerges as one of the most encouraging techniques in which to harness intermittent renewable power sources and store the energy these provide as a clean-burning and sustainable fuel. Nevertheless, efficacious formation of H
2 and O
2 is of little usage if such products cannot be kept separate and there are major dares linked with preserving suitable separation between H2 and O2 during electrolysis driven by intermittent renewable sources. In this work, a short view of fresh advance in the field of decoupled electrolysis for water splitting is presented and the potential that this technique has for enabling a range of other sustainable chemical processes is explored. Between such chemical processes, electrochemical disinfection (ED) remains a great promise in disinfecting water. This work suggests the application of ED in the EWS compartment producing O2 besides the other compartment producing H
2. Similarities between the two processes include that both of them use electric current for their realization. For the first one, H
2 and O
2 are produced separately in two cells. The suggested idea here is to use EWS device for producing H2 in one cell and producing O
2 in the second cell in which water may be disinfected by the electric field application and the electric current passage. Disinfection efficiency would be enhanced by the presence of O2. Practical examinations have to be conducted to determine the best scheme in terms of dimensions and disinfection efficiencies.
Now, fossil fuels (as coal, oil, and natural gas) stay the world’s main sources of energy [1]. Nevertheless, greenhouse gases (like CO2) that are produced through burning such fuels are related to general temperature augmentation [2] [3], shrinking ice sheets [4], ocean acidification [5], and extreme weather events [6]. Because the pollution rate and global energy demand persist to augment [7] [8] [9], suggesting energy solutions that do not depend on fossil fuels remains of vital significance. Renewable energy sources (like wind, solar, and tidal energy) form the most encouraging of such clean energy solutions, even if they are irregular [10]. As a result, supplying directly power from such sources could not be related to meet immediate energy demands [11]. Consequently, a technique of storing the energy produced by such renewable sources is fundamental for dealing with renewably generated power [1].
In such circumstances, hydrogen (H2) is frequently presented as an encouraging “carbon neutral” energy carrier (i.e., fuel) [1]. In this system, renewably formed electricity is employed to electrolyze water (H2O) to produce H2 and oxygen (O2). The O2 could be let out to the atmosphere whereas the H2 is stored as a fuel. This H2 is later oxidized (either by burning or in a fuel cell) to regenerate H2O and to liberate energy. In fact, H2 is not a perfect fuel; however, it possesses several interesting features like its minimum poisoning, capacity to be transported safely over long distances via pipeline [12], and its elevated energy density per unit mass (three times bigger than that of gasoline) [13]. Further, sustainably sourced H2 may be utilized to decrease CO2 or nitrogen (N2) from the atmosphere to form carbon-neutral fuels and commodity chemicals (like hydrocarbons and ammonia). In several viewpoints, H2 could be adopted as the solution to a sustainable energy cycle [1].
This work suggests a short view of fresh advance in the field of decoupled electrolysis for water splitting is presented and the potential that this technique has for enabling a range of other sustainable chemical processes is explored. Between such chemical processes, electrochemical disinfection (ED) remains a great promise in disinfecting the air, water, and special surfaces of different nature such as drinking water, wastewater, pool water, and other water qualities or surfaces. An obvious direction on engineering details is intended especially those related to research on complex liquid systems, consideration of hazards observed from disinfection by-product generation, and interest to ameliorate cell design and disinfection technology. More interest is accorded to hybrid techniques to inspire originality, to utilize synergistic effects and to satisfy the needs of real system treatment under practical circumstances. This work suggests the application of ED in the EWS compartment producing O2 besides the other compartment producing H2.
2. Electrochemical Water Splitting (EWS)2.1. Electrochemical Storage of Renewable Energy
Electrolyzing water could be viewed in matter of its two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) [1]. Such half-equations vary slightly following the pH at which the electrolysis is performed. At low pH, the HER and OER proceed as follows (all potentials are vs. the standard hydrogen electrode, SHE):
2 H + + 2 e − → H 2 HER ( pH = 0 , E 0 = 0.00 V ) (1)
2 H 2 O → O 2 + 4 H + + 4 e − OER ( pH = 0 , E 0 = 1.23 V ) (2)
While, below alkaline circumstances, the half-reactions take place
4 OH − → O 2 + 2 H 2 O + 4 e − OER ( pH = 14 , E 0 = 0.40 V ) (3)
4 OH − → O 2 + 2 H 2 O + 4 e − OER ( pH = 14 , E 0 = 0.40 V ) (4)
As a result, there is an important electrical energy demand to operate H2O electrolysis [1]. In the ordinary circumstances, a potential difference of 1.23 V is the thermodynamic minimum requested to electrolyze H2O. Nevertheless, to conquer different kinetic and resistance barriers (and thus to operate considerable currents to flow for the OER and HER), more voltage is needed. Such supplementary voltage is known as overpotential that is a sum of the various additional potentials relating to concentration, ohmic resistances in the electrolyzer, and to the kinetic overpotentials for the individual HER and OER half-reactions [14]. One from the previous overpotentials, the overpotential demand for the OER has a tendency to control because the formation of O2 is a kinetically demanding four-electron, four-proton process [15] [16]. As a result, the OER is frequently viewed as the major kinetic bottleneck for the electrolytic production of H2 from H2O [1].
2.2. From Traditional to Decoupled Electrolysis
Water electrolysis happens below the effect of a direct current between two electrodes in a single cell [1]. Such crude form furnishes numerous disadvantages, the most undesirable of which remains the absence of isolation of the formed H2 and O2. As seen in Reactions (1)-(4), two moles of H2 are produced for every mole of O2 formed. Such gas-evolving reactions take place together, possibly generating a highly explosive mixture [17]. Industrially, this is avoided by employing membranes (or diaphragms) that isolate the compartment into anodic and cathodic cells. Big scale water electrolysis at high pH is performed utilizing a liquid alkaline electrolyte (concentrated aqueous KOH solution), at moderate temperatures (20˚C - 80˚C) with an asbestos diaphragm [18]. In such context, the anodic and cathodic pressures should be carefully regulated to prohibit gas permeation across the separator [19] [20] [21]. Great advance has been lately noted in fabricating solid polymer membrane electrolyzers in which an anion or proton exchange membrane (like Nafion) is utilized within a compressed cell stack [22] [23]. Even if comparatively costly, such cell designs could work at considerable pressure differentials, at outstanding running current densities, and without the necessity of caustic electrolytes. In such devices, the product streams are preserved separate, as gas crossover rates across the membranes are low [18] [21] [24].
The problem of separating the H2 and O2 of electrolysis begins to be more complicated when utilizing renewable energy sources, where the power inputs are usually variable and/or low [1]. In these situations, the low current densities that are reached correspond to low rates of gas formation. Further, such rates of gas generation could in turn start to attain the rates of gas crossover for some membranes, potentially leading to safety problems. A current density of 100 A/m2 is adopted as a useful benchmark for solar-driven electrolyzers, since this is the approximate current density expected of a water splitting device operating at 10% solar-to-fuels efficiency under “1 Sun” illumination (AM 1.5, 100 mW/cm2) [25]. In such context, crossover of H2 into the anodic cell would be a real probability and may be mostly dangerous, because the lower explosion limit of H2 in O2 is only 4 mol% H2 in O2 [26] [27] [28]. Moreover, although effective and safe gas separation may be obtained, any solar-to-hydrogen apparatus, in which the half-reactions of water splitting stay coupled (like in a traditional electrolyzer, as shown Figure 1), will be subjected to the fact that the rate of the comparatively easy HER would remain be restricted by the more sluggish OER. In such scenario, harnessing low pressures of H2 gas safely and efficiently from large solar-to-hydrogen arrays is nontrivial and stays an unsolved dare.
To this objective, fresh progresses have been observed to “decouple” such processes utilizing redox mediators [1]. Indeed, a mediator with a suitable redox potential could be used such that the OER is coupled with the reduction of the mediator, rather than the direct formation of H2. Likewise, the HER can be realized independently of the OER, via coupling H2 production to the re-oxidation of the mediator, rather than to water oxidation (Figure 1). With each half-reaction taking place separately, the HER could be performed at much enhanced rates
compared to that feasible in traditional water electrolysis. Further, the possibility to carry out the HER and OER both in different spaces (“spatial separation”) and at different times (“temporal separation”) considerably enhances flexibility for harvesting H2 efficiently and safely and greatly decreases the demand for any gas purification stages. The features requested of a suitable mediator are stability in both the oxidized and reduced forms and a reversible redox couple with a potential that resides between the onset potentials of the OER and HER. Consequently, decoupled electrolysis could be described as any process where the ultimate anodic and cathodic products of electrolysis are formed under at least one of the next situations: 1) at rates that are not intrinsically related to each other, 2) at different times to each other, or 3) in entirely different electrochemical cells to each other (Figure 2).
Since its beginning during 2013 [29], the field of decoupled electrolysis has progressed rapidly. However, few short reviews have been devoted to the subject to date. The first one being a short discussion by Wallace and Symes [30], the second being a short section in larger overview on water electrolysis by You and Sun [31] and the third a short review by Liu et al. [32]. McHugh et al. [1] presented a thorough discussion of this thrilling field, highlighting the opportunities for decoupled electrolysis in energy storage, energy conversion, and chemical synthesis.
2.3. Decoupled Electrochemical Water Splitting (EWS): Dares & Perspectives
In their discussion, McHugh et al. [1] presented the present state-of-the-art in decoupled electrolysis for water splitting, following the development of the field from its conceptualization in 2013 through to the several refinements of decoupled electrolysis that have since been improved [1]. During this march, crucial stages have been realized. Such steps comprised 1) the proof of solar-driven H2 generation employing decoupling techniques, 2) the invention of decoupling agents that could be involved to carry out one of the half-reactions of water splitting spontaneously (such as through manipulation of the temperature or via convenient selection of electrodes and/or catalysts), 3) the expansion of robust solid-state decoupling agents, 4) the conjunction of decoupling techniques with bipolar electrolysis, and 5) the implementation of decoupling techniques to reactions beyond water splitting (like coupling H2 generation with organic upgrading oxidation reactions or carrying out organic hydrogenation reactions utilizing protons and electrons obtained from water). In addition, decoupling could be utilized both for electrolytic processes (i.e., those needing a net energy input like water splitting) and galvanic processes (where spontaneous chemical reactions are harnessed to generate electrical power like in fuel cells).
However, numerous decisive dares stay in the expansion of decoupled electrolysis in terms of device complexity and overall system stability. In terms of the second, materials compatibility among the decoupling agents and different cell components (such as membrane separators) and the stability of the agents themselves to repeated redox cycling frequently stay unproven. This is attributed mostly to a shortage of information on the long-term efficiency of decoupled systems. Viable information on long-term system stability has to be acquired before commercial usages become certain. For the present, decoupled electrolysis systems frequently give rise to augmented demands for extra balance of plant (and thus require bigger complexity) contrasted to easier, coupled approaches [1].
3. Electrochemical Disinfection (ED)3.1. Presentation and Descriptions
Electrochemical disinfection (ED) may be viewed as a physicochemical technology of disinfecting water via applying electrochemistry [33] [34] [35]. ED is generally a small-scale technique applied decentralized [36] [37] [38]. Disinfectant formation and distribution inside water could be realized discontinuously or continuously in flow-through mode or as chemicals’ injection to the devices from storage tanks [39] [40] [41]. Such technology is viewed as being sophisticated, not difficult to command, and avoiding storage and handling of toxic chemicals [42] [43] [44].
ED is generally founded on the oxidation power of disinfectants in the electrode layer or the bulk of electrolytes [45] [46]. Usually, harm to the intracellular enzyme system is referred to as the major cause for demobilizing microorganisms (MOs) [47] [48] [49]. According to Bergmann [33], electrical field contributions and pH-based impact could be disregarded in most ED situations. Several authors [50] [51] [52] [53] found that ED process, especially in the case of electrocoagulation (EC) [54] [55] [56], is greatly dependent on electric field and pH.
Pulsed electrical field technique, moderate electrical field handling, ohmic heating, plasma-related water treatment [57] [58], and ship body cleaning using conductive paintings are classified as special electrical field management and not discussed here [33].
MOs could as well be neutralized at relatively low electrode potentials in electron exchange reactions when they are closely adsorbed to electrodes [59] [60] [61]. Such technique remains time-consuming and not effective [33]. The more recent method is that of adsorbing MOs integrated with electrochemical oxidation [49] [62] [63]. At bigger potentials, oxidation and neutralizing of fixed MOs are likely if radicals are formed by electrodes possessing bigger oxygen overvoltage [64] [65] [66].
The function of direct oxidation by hydroxyl radicals (●OH) is frequently lower than anticipated. This is may be related to short radical lifetime, reaction competition, and when a relatively small number of MOs is adsorbed at the electrode [33] [67].
In the situation of gas (i.e., H2 from cathode and O2 from anode) production, MOs could be physically eliminated from the water (i.e., electroflotation [68] [69] ) and electrode surfaces [33] [70].
The plurality of disinfectant-producing methods may be performed in water, the synthesis of ferrates as powerful oxidants could be carried out in a molten electrolyte or in water [71] [72] [73] [74].
3.2. Usual Killing Agents Encountered in Electrochemical Disinfection (ED) Device
Killing agents may be produced via anodic reactions and rarer in cathodic reactions [33]. Table 1 lists the most important of them.
3.3. By-Product Troubles
As in chemical disinfection, taking into account by-products formation in ED is more and more imposed [98] [99] [100]. Table 2 summarizes by-product categorization [33].
3.4. Cell Designs
Cell geometries could be categorized in separator-divided or undivided cells with immersed electrodes, parallel plate electrodes, 3D-flow-by and flow-through electrodes, rods, and tubular electrodes in monopolar, bipolar, or mixed arrangement [75]. Lately, a multicylindrical cell design was announced, possessing six
Disinfectants formed in an ED apparatus [<xref ref-type="bibr" rid="scirp.109518-ref33">33</xref>]
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 O 3 − .
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.
Electrolysis by-products (EBPs) are the consequence of undesirable electrochemical reactions such as the anodic chlorate and the cathodic nitrite and ammonia formation [101] : 6HClO + 3H2O → 2ClO3− + 4Cl− + 12H+ + 3/2O2 + 6e− (6) NO 3 − + H2O + 2e− → NO 2 − + 2OH− (7) NO 2 − + 5H2O + 6e− → NH3 + 7OH− (8)
Disinfection By-Products (DBPs)
As portion of electrolytes, organic matter is mainly classified as Natural Organic Matter (NOM) [102] [103] [104] , Total Organic Carbon (TOC) [105] [106] [107] , and Dissolved Organic Carbon (DOC) [108] [109] [110] . They are typical precursors for the famous “Disinfection By-Products (DBPs)” [110] [111] [112] . Familiar from chemical disinfection [113] [114] [115] , DBPs are generated from reacting disinfectants with pollutants present in water [116] . In ED for drinking water, identical DBPs were detected when juxtaposed to chemical chlorination [53] [116] [117] . Reacting pathogen cell mater could be a supplementary source of DBPs (Figure 4) [118] [119] [120] .
Reaction By-Products (RBPs)
Reaction By-Products (RBPs) constitute all residual reactions in the electrode layers and bulk of solution. As an illustration is the chemical chlorate generation from free active chlorine species or from chlorite ions [118] .
cylindrical graphite electrodes [121]. Diverse innovation divulges from literature on suggesting 3D-BDD foam electrodes [33] [122] [123].
Mesh-like electrode structures are also developed [124] [125]. Recently, 3D activated carbon electrodes are exemplary for the mostly 2-step technique of electro-adsorption [33].
3.5. Mathematical Modeling
In applied electrochemistry, mathematical modeling emerged since several decades [33]. Now, strong simulation programs are accessible. Relating to ED implementations, the next usual modeling targets could be practically categorized: 1) quantification of disinfection findings concerning disinfectant formation and decomposition [126] [127], 2) current density distribution for reducing cell voltage [128], 3) averting electrode deterioration and by-product formation [33], 4) quantification of non-ideal flow behavior and, 5) assessment of probable reaction paths [129], etc.
3.6. Perspectives
In latest ED investigation, three main trends could be recognized: 1) augmented attempts in study for by-products and their likely poisoning, 2) application of fresh materials, frequently at the nanoscale [130], 3) process integrations/design of hybrid ED techniques [33] [131].
In electrochemical engineering, amelioration of electrode materials in terms of structure, yield, lifetime, and different indicators remains a main objective. Indeed, material issues concerning assistive, pre-treatment and post-treatment methods are more and more discussed as illustrated in nanotechnology-based electrode structuring [96] [124] [132], filter selectivity improvement [33] [133], and for numerous additional technology components.
Inventions are foremost related to hybrid processes [33]. For wastewaters [134] [135], adopting the direct ED is not suitable due to an uncontrolled reaction scheme with unknown intermediates and final products [136] [137] [138]. This is why coupling single treatment methods to integrated ones, as typical for Advanced Oxidation Processes (AOPs) [63] [64] [139], has been adopted [49] [61] [62].
Individual processes could be integrated in a minimum of two fashions: stepwise one after the other (in one or two devices), and combined into one (Table 3). As an illustration, in terms of by-product generation, it is logical to irradiate water in an initial stage and then, in a second stage, to treat using a chlorination method; in contrast, the irradiation of formerly chlorinated water could form
Most important hybrid processes dealing with electrochemical disinfection (ED) [<xref ref-type="bibr" rid="scirp.109518-ref33">33</xref>]
Hybrid processes
Description
Electrocoagulation (EC)/Electro-Fenton (EF)
Electrocoagulation (EC) process has the potential to kill pathogens efficiently and economically as the cost for electrode materials (Fe, Al) are relatively minor [143] [144] [145] . Several researchers merged EC with other techniques [146] [147] [148] . Other scientists juxtaposed EC to different techniques like Electro-Fenton (EF) [33] . EF with an in situ formation of ●OH is affiliated to AOPs and frequently proposed for treating wastewater [139] . Comparatively to EC, researches depicted better disinfection impacts of the EF method [149] [150] .
ED/filtration
Filtration could be used with filters possessing defined pore size distribution as with nanopore-filters [151] [152] [153] . This permits filtration of organic matter and MOs [154] [155] . If pursued by ED, disinfection performance could be attained and by-product generation will be reduced. Supplementary adsorption after filtration may ameliorate the yields [33] . Different original design is using reactive membranes [156] [157] [158] . Membrane-integrated electrodes could participate to membrane disinfection from time to time or add disinfecting species to the water flowing through [159] [160] .
ED/adsorption
High surfaces of adsorbing materials help them to adsorb MOs on uncharged or charged surfaces [161] [162] . In reverse or changed electrode potential, MOs could be repulsed and electrochemically demobilized [163] . Last essential functionality is once more the adsorption of products and by-products after a first-step ED procedure [164] .
ED/photocatalysis
The semiconductor composition of Mixed Metal Oxide (MMO) electrode material makes it interesting for being merged with irradiation (electro-photocatalytic disinfection [165] [166] [167] . Researchers examined usual issues, concepts and tendencies [165] [166] . Scientists focused on efficiency estimation [167] , usage of nanomaterials and novel electrode design [33] , disinfection by-products, and Cl2 generation [33] .
more by-products. One more benefit is the reservoir effect that could not be attained by sole UV disinfection [140] [141] [142].
4. A Bridge between Electrochemical Water Splitting (EWS) and Electrochemical Disinfection (ED)
We have briefly discussed EWS and ED techniques. Similarities between the two processes include that both of them use electric current for their realization. For the first one, H2 and O2 are produced separately in two cells. Such gases may be produced in ED especially for electroflotation and EC processes. The suggested idea here is to use EWS device for producing H2 in one cell and producing O2 in the second cell in which water may be disinfected by the electric field application and the electric current passage. Disinfection efficiency would be enhanced by the presence of O2.
As shown previously, Figure 2 illustrates three alternative decoupling strategies. Configurations (a) and (b) (Figure 2) seem to be more suitable for producing H2 and O2 as well treating water. In Figure 2(b), decoupled water electrolysis using nickel (oxy)hydroxides as a solid-state redox mediator is presented; and in Figure 2(c), Walsh’s bipolar electrode strategy for decoupled electrolysis is depicted.
5. Conclusions
To produce H2 and O2, electrolytic water splitting (EWS) emerges as one of the most encouraging techniques in which to harness intermittent renewable power sources and store the energy these provide as a clean-burning and sustainable fuel. Lately, this has conducted to an eruption in publications on EWS, most of them worked on increasing the productivity of the electrochemical reactions themselves. Decoupled electrolysis presents a solution to numerous of such dares through authorizing O2 and H2 to be formed at different times, at different rates, and even in completely different electrochemical cells. In this work, a short view of fresh advance in the field of decoupled electrolysis for water splitting is presented. On the other hand, ED remains a great promise in disinfecting water. This work suggests the application of ED in the decoupled electrolysis compartment producing O2 besides the other compartment producing H2. The main conclusions drawn are listed below:
1) During the last seven years, decoupled electrolysis for water splitting has known an outstanding expansion following the development of the field from its conceptualization [1]. Decoupling could be utilized both for electrolytic processes and for galvanic processes. However, numerous decisive dares stay in the expansion of decoupled electrolysis in terms of device complexity and overall system stability. In terms of the second, materials compatibility among the decoupling agents and different cell components and the stability of the agents themselves to repeated redox cycling frequently stay unproven. This is attributed mostly to a shortage of information on the long-term efficiency of decoupled systems. Viable information on long-term system stability has to be acquired before commercial usages become certain. For the present, decoupled electrolysis systems frequently give rise to augmented demands for extra balance of plant contrasted to easier, coupled approaches [1].
2) ED is very innovative and developing technology domain. Even with all advance noted in fundamental study, pilot investigations, and usage, the maturity for numerous disinfection techniques stays weak and some issues could not be managed such as [33]: a) ED processes remain not often famous; b) application circumstances require preliminary investigations for selecting optimally the disinfection devices and method, and for pre-treatment and post-treatment stages; c) strictest rules and demands occur in the potable water industry with limiting by-product concentration at μg/L level span especially for highly-oxid- ative anodes and; d) fresh ED processes could be costly what renders them uncompetitive and restricts their diffusion.
3) We have briefly discussed EWS and ED techniques. Similarities between the two processes include that both of them use electric current for their realization. For the first one, H2 and O2 are produced separately in two cells. Such gases may be produced in ED especially for electroflotation and EC processes. The suggested idea here is to use EWS device for producing H2 in one cell and producing O2 in the second cell in which water may be disinfected by the electric field application and the electric current passage. Disinfection efficiency would be enhanced by the presence of O2. Practical examinations have to be conducted to determine the best scheme in terms of dimensions and disinfection efficiencies.
Acknowledgements
The Research Deanship of University of Ha’il, Saudi Arabia, has funded this research through the Project RG-20 113.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.
Cite this paper
Ghernaout, D. and Elboughdiri, N. (2021) Towards Combining Electrochemical Water Splitting and Electrochemical Disinfection. Open Access Library Journal, 8: e7445. https://doi.org/10.4236/oalib.1107445
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https://doi.org/10.1016/j.scitotenv.2018.05.012Ait Messaoudene, N., Naceur, M.W., Ghernaout, D., Alghamdi, A. and Aichouni, M. (2018) On the Validation Perspectives of the Proposed Novel Dimensionless Fouling Index. International Journal of Advanced and Applied Sciences, 5, 116-122.
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https://doi.org/10.1016/j.cej.2018.09.136Belhout, D., Ghernaout, D., Djezzar-Douakh, S. and Kellil, A. (2010) Electrocoagulation of a Raw Water of Ghrib Dam (Algeria) in Batch Using Iron Electrodes. Desalination and Water Treatment, 16, 1-9. https://doi.org/10.5004/dwt.2010.1081Irki, S., Ghernaout, D., Naceur, M.W., Alghamdi, A. and Aichouni, M. (2018) Decolorization of Methyl Orange (MO) by Electrocoagulation (EC) Using Iron Electrodes under a Magnetic Field (MF). II. Effect of Connection Mode. World Journal of Applied Chemistry, 3, 56-64. https://doi.org/10.11648/j.wjac.20180302.13Cotillas, S., Llanos, J., Cañizares, P., Mateo, S. and Rodrigo, M. (2013) Optimization of an Integrated Electrodisinfection/Electrocoagulation Process with Al Bipolar Electrodes for Urban Wastewater Reclamation. Water Research, 50, 1741-1750.
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https://doi.org/10.1016/j.desal.2011.01.032Ghernaout, D. and Elboughdiri, N. (2020) Urgent Proposals for Disinfecting Hospital Wastewaters during COVID-19 Pandemic. Open Access Library Journal, 7, e6373. https://doi.org/10.4236/oalib.1106373Ghernaout, D. and Elboughdiri, N. (2020) On the Other Side of Viruses in the Background of Water Disinfection. Open Access Library Journal, 7, e6374.Ghernaout, D. (2020) Enhanced Coagulation: Promising Findings and Challenges. Open Access Library Journal, 7, e6569.Kellali, Y. and Ghernaout, D. (2019) Physicochemical and Algal Study of Three Dams (Algeria) and Removal of Microalgae by Enhanced Coagulation. Applied Engineering, 3, 56-64.Djezzar, S., Ghernaout, D., Cherifi, H., Alghamdi, A., Ghernaout, B. and Aichouni, M. (2018) Conventional, Enhanced, and Alkaline Coagulation for Hard Ghrib Dam (Algeria) Water. World Journal of Applied Chemistry, 3, 41-55.
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https://doi.org/10.5004/dwt.2009.116García-Segura, S., Lanzarini-Lopes, M., Hristovski, K. and Westerhoff, P. (2018) Electrocatalytic Reduction of Nitrate: Fundamentals to Full-Scale Water Treatment Applications. Applied Catalysis B: Environmental, 236, 546-568.
https://doi.org/10.1016/j.apcatb.2018.05.041Ghernaout, D. (2018) Disinfection and DBPs Removal in Drinking Water Treatment: A Perspective for a Green Technology. International Journal of Advanced and Applied Sciences, 5, 108-117. https://doi.org/10.21833/ijaas.2018.02.018Ghernaout, D. and Elboughdiri, N. (2020) Solar Treatment in the Core of the New Disinfection Technologies. Chemical Science and Engineering Research, 2, 6-11.
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https://doi.org/10.1080/01919512.2012.721715Ghernaout, D. and Elboughdiri, N. (2020) Towards Enhancing Ozone Diffusion for Water Disinfection—Short Notes. Open Access Library Journal, 7, e6253.Ghernaout, D. and Elboughdiri, N. (2020) Electrochemical Technology for Wastewater Treatment: Dares and Trends. Open Access Library Journal, 7, e6020.Ghernaout, D. (2020) Demobilizing Antibiotic-Resistant Bacteria and Antibiotic Resistance Genes by Electrochemical Technology: New Insights. Open Access Library Journal, 7, e6685. https://doi.org/10.4236/oalib.1106685Ghernaout, D. and Elboughdiri, N. (2020) Disinfection By-Products Regulation: Zero ng/L Target. Open Access Library Journal, 7, e6382.Ghernaout, D. and Elboughdiri, N. (2020) Foresight Look on the Disinfection By- Products Formation. Open Access Library Journal, 7, e6349.Boucherit, A., Moulay, S., Ghernaout, D., Al-Ghonamy, A.I., Ghernaout, B., Naceur, M.W., Ait Messaoudene, N., Aichouni, M., Mahjoubi, A.A. and Elboughdiri, N.A. (2015) New Trends in Disinfection By-Products Formation upon Water Treatment. Journal of Research & Developments in Chemistry, 2015, Article ID: 628833.
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