Continuously Press the Switch Twice It Will Enter the 3 minute Electrolysis Mode

Electrolysis

Electrolysis in the presence of hydrogen peroxide constitutes the second step, to achieve oxidation of the remaining recalcitrant organic compounds.

From: Waste Management Series , 2006

Source reduction, waste minimization, and cleaner technologies

Chaudhery Mustansar Hussain , ... Samiha Nuzhat , in Source Reduction and Waste Minimization, 2022

2.5.1 Electrolysis

Electrolysis is the process that uses electric current to run a non-spontaneous chemical reaction. It is a commonly used reusing technique that recovers useful resources from waste materials. It is mostly used to isolate valuable metals and organic compounds from waste in electrolysis cells ( Zhang and Angelidaki, 2014). Electrolysis cells are designed specifying minimization of certain waste types. In this regard, microbial electrolysis cells can be a suitable example that combines biological and chemical waste minimization techniques to ensure better yield of recovered resources (Zhang and Angelidaki, 2014). Such cells are still an emerging technology that has potential to generate hydrogen gas, biofuels, and other organic compounds recovery (Lu and Ren, 2016). In this process, a voltage supply is required to smoothly run the process ensuring energy supply. Fig. 2.7 illustrates a basic structure of such microbial electrolysis cell that can be modified to minimize waste (Kadier et al., 2016).

Figure 2.7. Schematic representation of microbial electrolysis cell used for waste minimization.

Innovative researches are going on to improve the efficiency of the electrolysis cells in terms of resource recovery by combining other chemicals in the cells. For instance, integration of ferrous activated persulfate oxidation with an electrolysis cell is found to be able in disrupting the protective barrier of complex waste materials present in sludge (Zhen et al., 2013). Electrolysis can also help to treat waste leachate from both solid and liquid waste that will minimize exposure and hazard cause by waste materials (Vlyssides et al., 2001). However, considering expenses and energy efficiency, microbial electrolysis cells are more common in waste minimization plants. However, as this process also requires high energy and harmful chemicals, it is not fully ecofriendly. But the efficiency of the process is quite satisfying.

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Integration of microbial electrolysis cells with anaerobic digestion to treat beer industry wastewater

Thangavel Sangeetha , ... Wei-Mon Yan , in Integrated Microbial Fuel Cells for Wastewater Treatment, 2020

15.2.1.3.3 Maintenance of reactor stability

The ME process has been proved to maintain the stable operation of an AD reactor in several ways. ME process can be used to alter and control the main processes in AD. Combining AD with an ME process resulted in a higher level of biogas production and enhanced methane production. The introduction of ME in the recirculation loop of a thermophilic UASB resulted in a higher tolerance of the digester to a severe drop in pH due to the addition of an acetate pulse to the system. Insertion of the cathode electrode in an AD reactor resulted in high CH₄ production and COD removal. The introduction of anode and cathode in the sludge bed of a UASB and a Continuous Stirred Tank Reactor (CSTR) also resulted in increased methane production (Liu et al., 2019). Thus ME can also be employed for postdigestion polishing of highly loaded wastewaters, leading to side products such as H₂.

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Energy from Wastewater Treatment

S.Z. Ahammad , T.R. Sreekrishnan , in Bioremediation and Bioeconomy, 2016

14.1 Microbial Electrolysis Cell

MEC is a variation of the mediator-less MFC. Energy is generated by means of electricity in MFCs by the metabolic activity of the bacteria during decomposition of organic compounds present in wastewater. In MECs, the metabolic process is partially reversed to generate hydrogen or methane by applying a potential difference across the electrodes. The externally supplied electrical energy to the system is used to supplement the voltage generated by the microbial decomposition of organics by the bacteria. The resultant electrical energy should be sufficient to electrolyze the water to produce hydrogen or to produce methane by reducing carbon dioxide. A complete reversal of the MFC principle is found in microbial electrosynthesis, in which carbon dioxide is reduced by bacteria using an external electric current to form multicarbon organic compounds (Call and Logan, 2008).

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Interconnected Electricity and Natural Gas Supply Chains: The Roles of Power to Gas and Gas to Power

Kaveh Rajab Khalilpour , in Polygeneration with Polystorage for Chemical and Energy Hubs, 2019

3.2 Electrolysis

Electrolysis is not a new technology. It was invented in 1800 by William Nicholson and Anthony Carlisle, using voltaic current. The invention has an interesting story: It was a few weeks after Alessandro Volta revealed his invention of the voltaic pile that William and Anthony decided to replicate Volta's experiment. In brief, during the experiment they accidentally contacted wires with water and observed some gases, which were found to be hydrogen and oxygen. This led to the birth of the new science, "electrochemistry" [27].

The main technical route in the PtG approach is the use of electrical energy for electrolysis of water to hydrogen (H₂O(l)   ➔   ½ O₂(g)   +   H₂(g) ΔH _r  =   +   285.8   kJ/mol-H₂O). The two products of this process are hydrogen and oxygen, with hydrogen being the most favored clean energy source. It can then be used in numerous hydrogen-demanding applications as a sustainable feed. It is noteworthy that majority of the ~   50 million tonnes annual hydrogen demand [28] is currently supplied by fossil fuels through syngas generation, which is a sustainability concern.

An alternative application for the generated hydrogen is to convert it back to electrical power in fuel cells (see Fig. 6) with the combustion exhaust being pure water. Bergen [29], in his PhD thesis, and Gahleitner [28] carried out comprehensive studies of PtG pilot plants for renewable-based hydrogen production. The earliest plant in the lists of the two studies is Solar-Wasserstoff-Bayern, built in Germany in 1986. The system comprised a 370-kW_p PV system, two low-pressure and high-pressure alkaline electrolysis technologies (211   kW_el at 1   bar and 100   kW_el at 31   bar), and three types of fuel cell technology [30].

Over the years, three major electrolysis systems have been developed: alkaline electrolysis (AEL), polymer electrolyte membrane (PEM), and solid oxide electrolysis (SOEC). As discussed by Kreuter and Hofmann [31], the technologies can be assessed based on the four key factors, efficiency, operability, safety, and costs. Given that several review studies of electrolysis exist (e.g., [32,33]), we briefly list the key features of the three electrolysis technologies in Fig. 8. The most mature technology is AEL, which is cheaper than the others in installation costs, though expensive in maintenance due to corrosiveness. AEL, however, suffers from operational inflexibility when integration with renewable-based fluctuating power sources is desired. It can take up to 1   h from a cold start. PEM, due to its membrane solid nature, is very flexible in operation. However, as is general for all membranes, its life span is short and thus it is expensive in comparison with AEL. Both AEL and PEM are mature technologies, whereas SOEC is in the laboratory development stage. SOEC operates at high temperatures to minimize power consumption by reducing cell voltage. Due to its superior efficiency compared with the other two technologies, SOEC is a promising technology, although there are numerous technical issues (especially heat integration) to be resolved [34]. In terms of pressure, all three technologies favor high pressures for higher hydrogen purity and overall efficiency. Note that other renewable-based H₂ generation technologies exist, such as photolysis [35], which are beyond the scope of this study of electrical power utilization.

Fig. 8. Three major electrolysis technology types.

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Organic pollutants from E-waste and their electrokinetic remediation

Don Liyanage , Janitha Walpita , in Handbook of Electronic Waste Management, 2020

8.2.1 Electrolysis

Electrolysis is the decomposition of water at electrodes when an electric field is applied. In this process oxidation takes place near anode generating hydrogen ions (H ⁺) and oxygen (O₂), and reduction takes place near cathode generating and hydroxyl ions (OH⁻) and hydrogen (H₂). These reactions are shown by the following equations (Cameselle et al., 2013; Sharma and Reddy, 2004):

$2{\mathrm{H}}_2\mathrm{O}\to 4{\mathrm{e}}^{-}+{\mathrm{O}}_2+4{\mathrm{H}}^{+}{\mathrm{E}}_0=-1.229\mathrm{V}$

$4{\mathrm{H}}_2\mathrm{O}+4{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2+4{\mathrm{OH}}^{-}{\mathrm{E}}_0=-0.828\mathrm{V}$

The process of electrolysis leads to changes in the soil pH near the electrodes. The region near anode develops a low pH of about 2 whereas near the cathode it increases up to 11 or 12. The hydrogen and hydroxyl ions move both due to electromigration and diffusion. The hydrogen ions being smaller than the hydroxyl ions tend to travel faster leading to rapid acid front migration than the base front migration (Sharma and Reddy, 2004). The acid dissolves the usual cations in the soil or precipitates and helps cation removal. If the contaminants are anionic, the acid front would increase adsorption and reduce the contaminant removal. Both the acid and base front will influence the zeta potential of the soil impacting the flow.

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Nuclear Hydrogen Production

Shripad T. Revankar , in Storage and Hybridization of Nuclear Energy, 2019

4.2.1 Low-Temperature Water Electrolysis

Electrolysis has been in use since the 1890s to split water into hydrogen and oxygen to supply primarily for chemical industries. Though electrolysis is more expensive than steam reforming of natural gas, it has advantages for generating hydrogen at small facilities for localized high-purity hydrogen and oxygen supplies, and it can meet the need of storage requirement for intermittent renewable technologies. Electrolysis technologies can be divided in two basic categories, alkaline liquid electrolyte using potassium hydroxide (KOH) and acid electrolyte with solid polymer as a proton-exchange membrane (PEM). In both technologies, water is fed into the reaction electrolyte and is subjected to an electric current that causes dissociation, after which the resulting hydrogen and oxygen atoms are put through an ionic transfer mechanism that causes the hydrogen and oxygen to accumulate in separate physical streams. Electrolysis of water is a combination of two half reactions as shown below for acid and alkaline electrolytes:

Acid electrolyte:

$\text{Anode}:{\mathrm{H}}_2\mathrm{O}\to {\text{2H}}^{+}+0.{\text{5O}}_2+{\text{2e}}^{-}$

$\text{Cathode}:{\text{2H}}^{+}+{\text{2e}}^{-}\to {\mathrm{H}}_2$

Alkaline electrolyte:

$\text{Anode}:{\text{2OH}}^{-}\to {\mathrm{H}}_2\mathrm{O}+0.{\text{5O}}_2+{\text{2e}}^{-}$

$\text{Cathode}:{\text{2H}}_2\mathrm{O}+{\text{2e}}^{-}\to {\mathrm{H}}_2+{\text{2OH}}^{-}$

Overall reaction:

${\mathrm{H}}_2\mathrm{O}\to {\mathrm{H}}_2+0.{\text{5O}}_2$

Fig. 4.3 shows the operation principle of electrolysis with alkaline and PEM electrolyzers. Oxygen evolution occurs at the anode; hydrogen evolves at the cathode. In an alkaline electrolysis cell containing an aqueous caustic solution with usually 20%–40% KOH or NaOH (typically 30%), electric energy is applied to two electrodes. The cathode electrodes typically are made of low-carbon steel mesh or nickel-coated low-carbon steel mesh. The anode is made of alkali and oxidation-resistant materials like nickel-coated low-carbon steel or nickel series metals. Electrode catalysts such as Pt on which reaction occurs more easily are sometimes used. A porous diaphragm works for preventing mixture of product gases and direct contact of electrodes. Water decomposes at the cathode to H₂ and OH⁻, where the latter migrates through the electrolyte and a separating diaphragm and discharges at the anode, liberating the O₂. The hydrogen is readily extracted from the water when directed into a separating chamber. Operation temperatures are limited to <   150°C to avoid corrosion problems; typically, ~   90°C is used. The ideal reversible cell potential needed to split water is 1.229   V at 25°C and 0.1   MPa, which corresponds to a theoretical dissociation energy of Gibbs free energy of formation Δ  G _o  =   237   kJ/mol or an electricity demand of 3.56   kW   h/Nm³ of H₂. However, the realistic cell voltages are 1.7–2.1   V to account for irreversible processes in the reaction mechanism where overpotential of electrodes and ohmic resistance of cell components contribute to the losses. Additional losses are due to gas expansion at the electrodes and to maintain the operation temperature. The electric energy requirement is in the order of 4–4.5   kWh/Nm³ of H₂, corresponding to an efficiency of 80% and higher. For electrolysis, the theoretical amount of water required is 0.8   L/Nm³ of H₂; in practice, 1.0   L/Nm³ is required.

Fig. 4.3. Operation principles of alkaline and proton-exchange membrane (PEM) water electrolysis.

A PEM electrolyze is a PEM fuel cell operating in reverse mode. In PEM electrolysis, water is fed into channels of the anode side of the cell. The water flows from the plate to the anode through the current collector and reacts to split into protons, oxygen, and electrons. Current collectors are porous conductors that allow electrons to transfer from electrode to outer circuit and allow reactant gas from bipolar plate to electrode. The protons migrate through the PEM to cathode side, where it combines with electron to form hydrogen molecule at the cathode. Oxygen gas remains behind in the water. As this water is recirculated, oxygen accumulates in a separation tank and can then be removed from the system. Hydrogen gas is separately channeled from the cell stack and captured. The PEM also serves as a separator of product gases. Solid perfluorosulfonic acid polymer membranes, such as Nafion of DuPont, the United States, are typically used because of its excellent thermal resistance and oxidation resistance. Electrodes come in contact directly with the PEM to avoid interface electric resistance, since corrosion resistance to strong acidity of the PEM is required for electrodes. Typically, platinum group metal, alloy, and oxide of platinum are used for the porous electrodes. In PEM electrolyzer, cathode overpotential is the main source of the total cell overpotential, and it is influenced by selection of material. Typically, oxides of Ir and Ru or metallic platinum are used for cathode material. These materials are often mixed with inert components for structural stability.

The electrolysis is attractive due to its design, simplicity, and the flexibility of accepting virtually any nuclear reactors that generate electricity. The nuclear reactor couples to the process simply via electric transmission, meaning that there is no fluid-thermodynamic connection, such that distributed production of hydrogen close to end user of hydrogen is possible with electricity grids.

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Ocean In Situ Sensors Crosscutting Innovations

Eric Delory , ... Seyed Morteza Sabet , in Challenges and Innovations in Ocean In Situ Sensors, 2019

4.3.3.4 Seawater Electrolysis

The electrolysis chlorination system ( Fig. 4.3.8A) can be found on monitoring stations (Fig. 4.3.8B) [13,14] and "Ferry Box" instruments that use pumping circuitry, the protection is known as a "global chlorination" scheme [15]. In this way the whole circuitry is protected at the same time as the sensors.

Figure 4.3.8. (A) Seawater electrolysis principle. (B) Global protection. (C) Localized protection.

Source: L.Delauney.

Another electrolysis chlorination scheme can be found on a few autonomous sensors; it consists of protecting only the sensing area of the sensor (Fig. 4.3.8C). The electrolysis is performed on a very restricted area and, consequently, the energy needed is very low and compatible with autonomous deployment. Very few commercial instruments are equipped with such a scheme [16]. This is because the adaptation to the sensor-transducing interface can be difficult for some applications. Additionally, the energy required for this technique (240   mW) is still too high for use in long-term, low-energy deployments such as deep-sea standalone observatories.

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Resource Recovery and Recycling from Metallurgical Wastes

S. Ramachandra Rao , in Waste Management Series, 2006

11.1.3.5 Electrolytic Decomposition of Cyanide and Possible Recovery of Gold

Electrolysis of cyanide solution leads to discharge of cyanide ion at the anode, where it is oxidized (anodic oxidation). Cyanide is completely broken down to carbon dioxide, nitrogen and ammonia, with cyanate as an intermediate product ( Green and Smith, 1972). The probable anodic reactions are as follows:

(11.8) $\begin{array}{c}\begin{array}{cc}{\text{CNO}}^{-}& \begin{array}{cc}\to & \text{CNO}+\text{e}\end{array}\end{array}\\ \begin{array}{cc}5\text{CNO}+6{\text{H}}_2\text{O}& \begin{array}{cc}\to & 5{\text{CO}}_2+4{\text{NH}}_3+\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\text{N}}_2\end{array}+\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\text{O}}_2\end{array}\end{array}$

Urea may also be produced (Hillis, 1975) by the reaction,

(11.9) $\begin{array}{cc}\text{CNO}+2{\text{H}}_2\text{O}& \begin{array}{cc}\to & \text{CO}{\left({\text{NH}}_2\right)}_2+\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\text{O}}_2\end{array}\end{array}$

The destruction of cyanide, however, is not complete; as the process continues, the waste electrolyte becomes less capable of conducting electricity. Typical anodic current density is around 200   A/m² for graphite electrodes. (Patterson, 1985). Low levels of residual cyanide, down to 0.1–0.4 mg/L, can be reached by electrolysis for sufficiently long time, 14–18 days. Final destruction of the residual cyanide may be done by chlorination.

Electrochemical work on cyanide from gold recovery plants has been the subject of a laboratory study by Dutra and coworkers (2002) for recovering the residual gold and simultaneously the cyanide. A gold rotating disk electrode is used as cathode and a titanium gore covered with iridium dioxide as anode. Gold and copper occur as their cyanide complexes, aurocyanide $\text{Au}{\left(\text{CN}\right)}_2^{-}$ and cuprocyanide $\text{C}\text{u}{\left(\text{CN}\right)}_3^{-}$ respectively. The electrochemical reactions are

(11.10) $\text{A}\text{u}{\left(\text{CN}\right)}_2^{-}+\begin{array}{cc}\text{e}& \begin{array}{cc}\to & {\text{Au}}^{\text{o}}+2{\text{CN}}^{-}\end{array}\text{and Cu}{\left(\text{CN}\right)}_3^{-}+\begin{array}{cc}\text{e}& \begin{array}{cc}\to & 3{\text{CN}}^{-}\end{array}\end{array}\end{array}$

Although the study indicates a potentially useful method to recover both metals and cyanide, the experimental details of this laboratory study described by the investigators indicate the need for careful controls such as reagents of analytical grade. Any potential application using industrial effluents has not been demonstrated.

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The properties of water

James G. Speight , in Natural Water Remediation, 2020

6.1 Electrolysis

Electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. The electrolysis of water is the decomposition of water into oxygen and hydrogen by the passage of an electric current. In the process, a DC electrical power source is connected to two electrodes, or two plates (typically made from some inert metal such as platinum, stainless steel, or iridium) which are placed in the water.

Water can be split into its constituent elements, hydrogen and oxygen, by passing an electric current through it. In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e⁻) from the cathode being donated to hydrogen cations to form hydrogen gas. Conversely, at the positively charged anode, an oxidation, reaction which generates oxygen gas and giving electrons to the anode to complete the equation (energy) balance:

${2\text{H}}^{+}\left(\text{aq}\right)+{2\text{e}}^{-}\to {\text{H}}_2\left(\text{g}\right)\left(\text{reduction}\text{at}\text{the}\text{cathode}\right)$

${2\text{H}}_2\text{O}\left(\text{l}\right)\to {\text{O}}_2\left(\text{g}\right)+{4\text{H}}^{+}\left(\text{aq}\right)+{4\text{e}}^{-}\left(\text{oxidation}\text{at}\text{the}\text{anode}\right)$

$\text{Overall}\text{reaction}:2{\text{H}}_2\text{O}\left(l\right)\to 2{\text{H}}_2\left(g\right)+{\text{O}}_2\left(g\right)\left(\text{overall}\text{reaction}\right)$

The acid-balanced reactions (above) predominate in acidic (low pH) solutions, while the base-balanced reactions predominate in basic (high pH) solutions. Thus:

${2\text{H}}_2\text{O}\left(\text{l}\right)+{2\text{e}}^{-}\to {\text{H}}_2\left(\text{g}\right)+{2\text{OH}}^{-}\left(\text{aq}\right)\left(\text{cathode}\text{reduction}\right)$

${2\text{OH}}^{-}\left(\text{aq}\right)\to 1/{2\text{O}}_2\left(\text{g}\right)+{\text{H}}_2\text{O}\left(\text{l}\right)+{2\text{e}}^{-}\left(\text{anode}\text{oxidation}\right)$

The number of hydrogen molecules produced is thus twice the number of oxygen molecules and, assuming equal temperature and pressure for both gases, the volume of the hydrogen gas produced is twice volume of the oxygen gas produced. The gases bubble to the surface, where they can be collected.

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Resources in the Near-Surface Earth

P.W.J. Glover , in Treatise on Geophysics (Second Edition), 2015

11.04.6.2 Electroosmosis

Electroosmosis is the movement of liquid induced by an applied electric potential across a porous material, capillary tube, membrane, microchannel, or any other fluid conduit. Because electroosmotic velocities are independent of conduit size, as long as the double layer is much smaller than the characteristic length scale of the channel, electroosmotic flow is most significant when in small channels. Although the effect is only of the order of a few millimeters per second, it has been used effectively for remediation of pollutants, dewatering, and chemical separation.

The process is formally the opposite of that that gives rise to streaming potentials. The applied electric potential difference acts upon that part of the charged diffuse layer that is mobile, leading to a gross fluid volume flow. Electroosmotic flow was reported first in 1809 by the Russian imperial scientist Ferdinand Friedrich von Reuβ (Reuβ, 1809), who made water to flow through a plug of clay by applying an electric voltage. Although Reuβ studied electrokinetic properties in detail, much was lost to fire in 1812 during Napoleon's occupation of Moscow.

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