## 2 Materials and Methods  
Tartrazine Yellow (TY) (chemical formulae C\({}_{16}\)H\({}_{10}\)Na\({}_{2}\)O\({}_{7}\)S\({}_{2}\)N\({}_{2}\)), obtained from Glentham Life Sciences, Chorsham, UK, was used to prepare a test solution with a concentration of 0.05 mmol L\({}^{-1}\) (26.72 mg L\({}^{-1}\)). Sodium chloride (Kemika, Zagreb, Croatia) was used as a supporting electrolyte in a concentration of 1 g L\({}^{-1}\). Hydrochloric acid and sodium hydroxide (Kemika, Zagreb, Croatia) were used to adjust the pH. All chemicals were analytical-reagent grade and were used without further purification. A 600 mL of solution was placed in a glass reactor for the EC process. The anode and cathode were made of aluminium alloy AA 2007 (surface area of 47 cm\({}^{2}\)) with the composition shown in Table 1.  
Before each measurement, the rectangle-shaped electrodes were ground with sandpaper grades from P280 to P800, cleaned ultrasonically with ethanol and deionised water, dried, weighed on the analytical balance, and then immersed in the test solution at a mutual distance of 3 cm. Electrodes were connected to the Wamptek DPS605U digital rectifier (60 V, 5 A) (Wamptek Electronic Co., Shenzhen, China), used for current adjustment. The solution was mixed with the Dlab MS-H-Pro+ magnetic stirrer (Dlab Scientific Co., Ltd., Beijing, China) at a constant speed of 150 rpm. The influence of current density (0.008, 0.016, and 0.024 A cm\({}^{-2}\)) on the efficiency of TY dye removal was measured. The duration of the EC process varied between 10 and 50 min, while the initial pH value of the solution ranged from 3.0 to 7.0. The experimental study was conducted through 20 separate EC processes, following a predetermined experimental plan presented in Table 2 using the Design-Expert 13 software (State-Ease. Inc., Minneapolis, MN, USA). During the EC process, changes in pH value, temperature (\(T\)), and concentration (\(c\)) of the TY solution were monitored. The pH value of the TY solution was measured every 5 min using a Mettler Toledo Seven Multi pH meter (Mettler Toledo, Greifensee, Switzerland). The temperature was measured using a Testo 925 thermometer (Testo SE & \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Element** & **Al** & **Cu** & **Mg** & **Fe** & **Si** & **Mn** & **Pb** & **Bi** & **Zn** \\ \hline wt.\% & 93.50 & 3.84 & 0.88 & 0.67 & 0.21 & 0.67 & 0.11 & 0.07 & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of alloy AA2007. Co. KGaA, Titisee-Neustadt, Germany) at 5 min intervals, with an accuracy of 0.1 \({}^{\circ}\)C. The dye concentration in the solution was determined spectrophotometrically using a Perkin Elmer Lambda 25 UV/VIS spectrophotometer (PerkinElmer U.S. LLC, Shelton, CT, USA) at 426.28 nm. Samples (10 mL) for concentration determination were taken at the beginning of the measurement (initial solution) and after 5, 10, 15, 30, 40, and 50 min, depending on the measurement duration. The change in the mass of the anode was determined by weighing it before and after the EC process using a Kern ALJ 160-4 NM analytical balance (Kern & Sohn GmbH, Balingen, Germany). The surface condition of the aluminium anode after the EC processes was examined using an MXFMS-BD optical microscope (Ningbo Sunny Instruments Co., (Yuyao City, Zhejiang Province, China) at a magnification of 200\(\times\). Also, after the electrocoagulation, the settling ability of the suspensions was determined by settling the suspension in a 500 mL cylinder and measuring the supernatant height at set time intervals. The solution was then filtered, and the sludge was dried and weighed. Electrogenerated sludge was characterised using a scanning electron microscope, Thermo Scientific Quatto F (FEG SEM, Hillsboro, OR, USA), with an EDS SDD detector Ultim(r)Max, Oxford Instruments (Abingdon, Oxfordshire, UK).