**6.7. Electro‐Fenton method**

Fenton reaction is a reaction between iron (II) and hydrogen peroxide resulting in the forma‐ tion of hydroxyl radicals (OH**•**), a non‐selective and strong oxidising agent [91]. As a result, this process has been used to oxidise organic pollutants in aqueous solution to carbon dioxide and water. However, Fenton process has the disadvantage of the high cost of procuring the reactants (hydrogen peroxide and iron (II)) and sludge generation. An improved technique, electro‐Fenton process, which is capable of overcoming the above‐mentioned hindrances and permits improved control of hydroxyl radical generation [92], has therefore been devised. Electro‐Fenton process involves cathodic reduction of iron (III) in solution to iron (II) with a potential of *E*<sup>o</sup> = 0.77 V/SHE. This process, often referred to as electrochemical catalysis, pro‐ duces the iron (II) at a faster rate and thus promotes the production of hydroxyl radical for enhanced pollutant oxidation process [92].

Evaluation of the electro‐Fenton process as an appropriate substitute technique for elimina‐ tion of phenol from a phenol simulated wastewater was conducted by Abdelaziz et al. [93]. They used a sacrificial iron anode as the source of iron (II), added hydrogen peroxide to the system externally and used nitrogen gas sparging to stir the batch reactor. They also examined the influence of some factors on the effectiveness of the electro‐Fenton process. Their results revealed 97% overall COD reduction of 50 mg/l pollutant concentration at optimum conditions of pH 3, the superficial gas velocity of 1.18 cm/s, current density (1.7 mA/cm<sup>2</sup> ) and hydrogen peroxide concentration of 1500 mg/l. They observed that COD removal percentage increased with increasing current density, hydrogen peroxide concentration and sodium chloride concen‐ trations but started decreasing, in all cases, beyond their respective optimum values. In addi‐ tion, consumption of energy and iron decreased as the initial pollutant (phenol) and sodium hydroxide concentrations were increased, but increased with an increase in the current density.

In their study, where they investigated the effectiveness of the electron‐Fenton process for removal of COD from paper mill wastewater, Un et al. [94] concluded that electro‐Fenton process is effective for removal of COD from tissue paper waste water. They achieved a COD removal efficiency of 80% within 60 min at 20 mA/cm<sup>2</sup> current density with 0.1 M hydro‐ gen peroxide concentration at pH 2. They noticed that though increasing the current density caused a corresponding increase in the COD removal, it also resulted in increasing energy consumption. Similarly, Rahmani et al. [95] have effectively applied the electro‐Fenton tech‐ nique to degrade phenol from aqueous solution. In this study, they applied a disposable iron anode as the source of ferrous iron and added the hydrogen peroxide manually. Highest degradation efficiency of 100% was obtained within 30 minutes at pH 3, 100 mg/l hydrogen peroxide concentration and 5 mA/cm<sup>2</sup> optimum conditions.
