**2.4 Colour removal efficiency**

The ultraviolet–visible spectrophotometer (Jasco V-670 spectrophotometer) was used to measure the wavelength (542 nm) of dye. The calculation of color removal efficiencies (CRE %) after electrocoagulation treatment was performed using the formula, as it is given in Eq. (1).

$$\text{Color removal efficiency} \left( \text{CRE@} \right) = \text{100} \ast \left( \mathbf{A}\_{\text{i}} - \mathbf{A}\_{\text{f}} \right) / \mathbf{A}\_{\text{i}} \tag{1}$$

Where Ai and Af were the absorbance of the dye in solution afore electrocoagulation and at the time *t*, respectively. Using a conductivity metre (Elico CM180) and a pH metre (Eutech), the electrical conductivity and pH of different dye concentrations were measured.
