Electrochemical device for the in-situ generation of trivalent iron and aluminum ions for coagulation in water treatment

Abstract

The present invention provides a compact electrochemical unit consisting of four metallic plates (iron or aluminum) arranged inside a cylindrical housing The plates are connected to a low-voltage power supply (maximum 40 V for safety). Water is pumped into the chamber through an inlet pipe, passes between the electrodes, and exits through an outlet. During operation, the electrodes release Fe³+ or Al³+ ions, depending on the electrode material. These ions induce coagulation of colloidal and suspended matter, thereby clarifying the treated water. The configuration allows for efficient ion release at low energy consumption, avoids chemical storage, and provides an easily scalable solution for both emergency and industrial water treatment.

Description

[0001] Electrochemical Device for the In-situ Generation of Trivalent Iron and Aluminum Ions for Coagulation in Water Treatment Technical Field The invention relates to water and wastewater treatment. More specifically, it concerns an electrochemical device designed to generate trivalent iron (Fe³⁺) or aluminum (Al³⁺) ions in situ, which are used as coagulants for the removal of colloidal and suspended impurities. Background Art Chemical coagulation is a widely used method in water treatment [1,2]. Traditionally, salts of iron or aluminum are externally dosed into treatment units [3]. However, these approaches increase operational costs, require chemical storage, and can pose handling risks. Electrocoagulation offers an alternative, where coagulants are generated in situ by dissolving metal electrodes through an applied electrical current [4]. Despite significant research, existing devices are often complex, require high voltage, or are inefficient in ion release. There is a need for a simple, safe, and efficient system that can be operated at low voltages and produce sufficient coagulant ions. Electrochemical methods have been effectively used in many studies for the removal of a wide range of pollutants from wastewater, including non-settling suspended solids (colloids) [5]. In this method, several electrodes with specific material and surface area are placed in wastewater and connected to an electric current with certain voltage and amperage. This makes it possible to remove organic pollutants. In electrochemical methods, not only dissolved organic compounds but also suspended particles, color, and harmful bacteria in wastewater are removed [6]. Commonly, three types of electrodes are used in electrochemical treatment: graphite, iron, and aluminum [7,8]. The use of iron and aluminum electrodes, in addition to direct oxidation of organic compounds, can also release trivalent iron or aluminum ions into the wastewater [9,10]. These ions have coagulating properties. They can neutralize the surface charge of colloidal suspended particles in water and create conditions for their aggregation into larger flocs. Part of these flocs usually settle to the bottom, and part of them float on the water surface. In this way, separation from water becomes possible. Therefore, electrochemical methods can easily remove both dissolved organic compounds and suspended solids from wastewater

[0011] . These methods are usually simple and low-cost. However, they are generally combined with other treatment methods to achieve the best results. In some industries, combinations of such methods are applied to achieve complete purification. Although wastewater treatment has been carried out using the above-mentioned methods, by arranging and combining them in a specific order, a powerful treatment plant for different types of industrial wastewater can be designed. Several pathways have been proposed for the oxidation of organic matter using electrochemical methods [12, 13]. The most important ones are: (a) direct oxidation on the anode, (b) indirect oxidation with hydroxyl radicals (^OH) on the inert anode, (c) Electro-Fenton and cathodic Fenton processes, (d) indirect oxidation with active chlorine in the presence of chloride, (e) sulfate electrolysis and generation of sulfate radicals, (f) other indirect oxidation pathways (such as anodic ozonation, peroxynitrite, etc.), and (g) cathodic reduction (cathodic catalysts and reductive decomposition). The sacrificial electrode can be iron or aluminum. If the sacrificial electrode is aluminum, Al³⁺ ions are released in the aqueous medium (Eq.1)

[0014] . If the sacrificial electrode is iron, Fe²⁺ and Fe³⁺ ions are released in the aqueous medium (Eq. 2)

[0015] . Using the following equations, it is possible to calculate howmany moles of metal ions are released in water per mole of electrode consumed.^^^^ → ^^^^ଷା ^ 3^^ି ^^^^^.1^^^^^ → ^^^^ଶା ^ 2^^ି ^^^^^.2^The Al³⁺ and Fe³⁺ ions in water undergo hydrolysis according to equations 3 and 4. The solid metal hydroxides (Al(OH)₃ or Fe(OH)₃) form flocs that capture colloids and suspended solids

[0016] . In the design, the balance of pH and alkalinity must beconsidered, since the hydrolysis process depends on pH.^^^^ଷା ^ 3^^ ^^ ^ ^ ାଶ → ^^^^^^^^^^ଷ ^^ ^ 3^^ ^^^^^.3^^^^^ଷା ^ 3^^ଶ^^ → ^^^^^^^^^^ଷ ^^^^ ^ 3^^ା ^^^^^.4^One of the important reactions in electrochemical treatment is the cathodic reduction of oxygen to hydrogen peroxide, which serves as a precursor for the electro-Fenton process (see Equation 5)

[0017] .^^ ^ 2^ ା ିଶ ^ ^ 2^^ → ^^ଶ^^ଶ ^^^^^.5^This reaction is used to produce hydrogen peroxide in situ. When combined with Fe²⁺ions, hydroxyl radicals are generated (as shown in the Equation 6).^^^^ଶା ^ ^^ଶ^^ଶ → ^^^^ଷା^. ^^^^ ^ ^^^^ି ^^^^^.6^The hydroxyl radical (^OH) is a very strong oxidant that attacks refractory organic compounds and mineralizes them

[0018] . In the electro-Fenton process, Fe²⁺ ions are electrochemically regenerated at the cathode

[0019] . The direct production of ^OH radicals on inactive anodes is another phenomenon that can occur during electrochemical wastewater treatment. The oxidation of water on the surface of an“inactive” anode takes place according to the following equation.^^ ^^ →. ^^^^ ^ ^ ା ିଶ ^ ^ ^^ ^^^^^.7^^^^^^. ^^^^ →. ^^ ^ ^^ଶ^^ → ^^^^ଶ ^ ^^ଶ^^ ^^^^^.8^Boron-doped diamond (BDD) and some metal oxide anodes enhance this indirect oxidation pathway

[0020] . This method is suitable for deep mineralization. Using Faraday’s law, the mass of dissolved metal or the number of moles of generated species can be calculated. To determine the number of moles of metal released into the water during the electrolysis process (n), Equation 9 is used, and to calculate the mass of metal released by the electrolysis process (m), Equation 10 is applied.^^^^^^ ൌ^^^^ ^^^^^.9^ ^^ ൌ ^^^^^^^^^^ ^^^^^.10^Where I is the current (A), t is the time (s), z is the number of electrons transferred per atom of metal (3 for Al³⁺, 2 for Fe²⁺), F is the Faraday constant (approximately 96,485 C^mol⁻¹), and M is the molar mass (g^mol⁻¹). These equations are applied to determine the electrode dimensions and to estimate the electrical charge required to generate the target coagulant dose. The input current density applied to the electrodes can also be calculated using Equation (11). ^^^^ ൌ^^ ^^^^^.11^ where j is the current density (amperes per square meter), I is the current (amperes), and A is the anode surface area (square meters). The treatment rate and electrode dissolution increase proportionally with the current density. Therefore, j should be selected to balance the production rate and the electrode’s service life. When chloride ions (Cl−) are present in the solution, during electrochemical reactions, these ions are first converted to molecular chlorine (Cl2) (Equation 12), and then water is hydrolyzed to produce HOCl / OCl⁻ (Equation 13)

[0021] . This process is called theindirect chlorination pathway.2^^^^ି → ^^^^ଶ ^ 2^^ି ^^^^^.12^^^^^ ା ିଶ ^ ^^ଶ^^ ↔ ^^^^^^^^ ^ ^^ ^ ^^^^ ^^^^^.13^ HOCl / OCl⁻ ions are oxidizers that remove organic compounds, but they can also form chlorinated by-products. If the feedwater contains chloride, this should be taken into account. The production of sulfate radicals through anodic persulfate is another oxidation pathway that occurs during the electrochemical treatment of wastewater(see Equations 14 and 15).2^^^^ଶି → ^ ଶ଼ି ିସ ^ଶ^^ ^ 2^^ ^^^^^.14^^^ ଶ଼ି .ିଶ^^ → 2^^^^ସ ^^^^^.15^The sulfate radical ^^^^ସ.ିis a strong oxidizer used for the decomposition of resistant organic compounds

[0022] . This pathway can be applied in advanced electrochemical oxidation. Reviewing various oxidation methods, especially when combined with electrochemical processes, shows that an efficient system can be achieved for removing persistent pollutants in industrial wastewater. This approach not only improves the quality of the treated effluent but also enables the reuse of water. Summary of Invention The present invention provides a compact electrochemical unit consisting of four metallic plates (iron or aluminum) arranged inside a cylindrical housing. The plates are connected to a low-voltage power supply (maximum 40 V for safety). Water is pumped into the chamber through an inlet pipe, passes between the electrodes, and exits through an outlet. During operation, the electrodes release Fe³^or Al³^ions, depending on the electrode material. These ions induce coagulation of colloidal and suspended matter, thereby clarifying the treated water. The configuration allows for efficient ion release at low energy consumption, avoids chemical storage, and provides an easily scalable solution for both emergency and industrial water treatment. Description 1. Device Structure A cylindrical chamber made of a non-corrosive material. Four metallic electrodes (iron or aluminum plates) are fixed within the chamber (see Figure 1). Electrodes connected to a transformer providing up to 40 V DC. Inlet and outlet pipes for continuous water flow. 2. Operating Principle When current flows, anodic dissolution occurs: Fe → Fe³⁺ + 3e⁻ or Al → Al³⁺ + 3e⁻ These trivalent ions hydrolyze in water to form metal hydroxides: Fe³⁺ + 3H₂O → Fe(OH)₃ + 3H⁺ Al³⁺ + 3H₂O → Al(OH)₃ + 3H⁺ The hydroxides aggregate to form flocs, which capture colloidal and suspended impurities. 3. Advantages ^ Safe low-voltage operation (≤40 V). ^ In-situ generation of coagulant reduces chemical handling. ^ Compact cylindrical design enables portable or modular use. ^ Increased efficiency in clarification due to uniform electrode arrangement. Brief Description of Drawings Figure 1: Rod electrodes in a cylinder electrocoagulation unit

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Claims

Claims 1. An electrochemical device for water treatment, comprising: a cylindrical housing; four iron or aluminum plate electrodes arranged within the housing; an inlet pipe for raw water and an outlet for treated water; an electrical transformer providing ≤40 V DC connected to the electrodes; wherein the electrodes, when energized, generate Fe³⁺ or Al³⁺ ions in situ for water coagulation.

2. The device of claim 1, wherein the electrodes are configured as parallel plates ensuring uniform current distribution.

3. The device of claim 1 or 2, wherein the cylindrical housing is designed to promote continuous water flow across the electrodes.

4. The device of claim 1–3, wherein the Fe³⁺ or Al³⁺ ions hydrolyze to form hydroxide flocs that aggregate colloids and suspended solids.

5. The device of any preceding claim, wherein the system is designed for safe operation at voltages not exceeding 40 V to minimize electrical hazards.

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