A glass reactor with working volume

A glass reactor with working volume of 300 mL was used for thermo-alkaline pretreatment. NaOH solution (5N) was used to adjust pH of sample to a value around 10. After that, sample was homogenized for 24 h at ambient temperature (28°C) and 2 h at 105°C. These conditions were optimized in a previous study [21]. Electro-Fenton pretreatment was carried out in a glass reactor connected to an electric generator ASF type 400/40.10. Two iron electrodes which were positioned approximately 2.5 cm apart from each other were used. The active surface area of electrodes was 0.16 dm2. Electrolysis experiments were operated in batch mode by treating 300 ml of raw WAS. The pH of WAS sample was adjusted to 3 by adding HCl solution (2N). Current density, reaction time, and H2O2 concentration were fixed, respectively, at 2.5 A/ dm2, 1 h, and 1.8 g/l as optimum conditions determined in previous study. During electrolysis treatment, continuous homogenization was maintained to avoid sedimentation of sample.