## 1 Introduction  
The deficiency of fresh water has become a significant concern worldwide, as its quality and supply for domestic and industrial purposes are constantly deteriorating due to pollution. Numerous sources cause the above, including almost all industries, agricultural and mining activities, and municipal wastewater [1; 2; 3]. However, despite their well-documented hazardous effects on aquatic life and people, dyes are essential substrates in the textile, printing and food industries. The annual production of all commercially available dyes reaches a staggering amount of over 800,000 tons [4; 5]. Among the various textile dyes, the most commonly used synthetic pigments are substances known as azo dyes, making up approximately 70% of the world's dye production. azo dyes are characterized by the appearance of one or more azo group(s) (-N=N-) in their molecular structure [6; 7; 8]. Over the past several years, numerous attempts have been made to find the most suitable and safe methods for dye removal, including physical, chemical and biological techniques. Among these methods, biological processes are often favored due to their low impact on the environment and cost-effectiveness [9; 10]. However, the high concentration of azo dyes and the presence of other chemicals (salts or surfactants) in the textile effluent repeatedly inhibited the process of azo dye biodegradation [1; 9; 10; 11; 12]. Hence, to improve the degradation of dyes, researchers have focused on integrating biological treatment and advanced oxidation processes (AOPs) [9; 13; 14]. The characteristic feature of AOPs is the production of highly active radicals, which could be generated through a series of complex physical and chemical processes, including ozonation [15], photocatalysis [16], photo-Fenton [17] and electrochemical oxidation [18]. One of the most extensively researched AOPs is the electrochemical degradation technique due to its simplicity, fast reaction rate, and high oxidation efficiency. Additionally, it can mineralize the dye without the necessity of using additional chemicals [19]. Moreover, the operational cost can be reduced by employing a renewable energy source to power the process. The electrochemical oxidation of the pollutant can be proceed either by direct oxidation of the dye on the anode's surface or by the indirect oxidation caused by hydroxyl radicals (-OH) formed during the process. Such oxidant spices are capable of oxidizing a wide variety of inorganic and organic pollutants [20; 21]. However, the Faradic efficiency of -OH production is inefficient compared to other more thermodynamically favorable water oxidation reactions occurring on the electrode-solution interface [22; 23; 24; 25; 26]. The above-mentioned reaction with their overpotential values is presented by Equations (1)-(3) below:  
\[\mathrm{H_{2}O}\rightarrow\ \mathrm{\cdot OH+H^{+}+e^{-}}\ \ \ \left(\mathrm{E^{0}}=2.74\ \mathrm{V}\right) \tag{1}\]  
\[2\mathrm{H_{2}O}\rightarrow\mathrm{H_{2}O_{2}+2H^{+}+2e^{-}}\ \ \left(\mathrm{E^{0}}=1.74\ \mathrm{V}\right) \tag{2}\]  
\[2\mathrm{H_{2}O}\rightarrow\mathrm{O_{2}+4H^{+}+4e^{-}}\ \ \ \left(\mathrm{E^{0}}=1.23\ \mathrm{V}\right) \tag{3}\]  
Nevertheless, most of the azo dyes are directly oxidized in lower potentials [27]; thus, electrodeposition methods are still a viable way to remove those pollutants. Moreover, electrochemical oxidation is characterized by the pollutant's rapid degradation rate (in the initial stage of the process), with decolorization efficiency ranging from 60 to over 90% depending on various conditions, such as current density or electrodes used [10; 18; 23; 28; 29]. Nonetheless, despite the high efficiency of such DC-powered systems, they still suffer from high electrical energy consumption, making them a relatively non-profitable method for dye removal. The above-mentioned issue could be resolved by applying an appropriately designed galvanic cell (cathode/anode) reactor.