Degradation of refractory compounds in industrial wastewaters by advanced technologies based on electrochemical and photochemical oxidation

Results are presented of a systematic experimental investigation aiming to eliminate refractory organics from industrial effluents, of high and non-biodegradable organic load, by two Advanced Oxidation Processes (AOPs). Bench scale experiments were performed with real wastewater samples collected from a pesticides manufacturing plant, of varying TOC content (800-1820 mg/L), to investigate the effectiveness of boron-doped diamond (BDD) anodic oxidation (AO), of H2O2 photolysis with UV-C irradiation (H2O2/UV-C), and their combination (i.e. AO/H2O2/UV-C) on the total organic carbon (TOC) removal. The effect of main operating conditions was investigated for both processes, separately and in combination. In the case of AO, TOC and COD were removed at a rate of 36.4 mgC/h and 89.5 mgO2/L, by applying a current density of 100 mA/cm2 and a recirculation flow rate of 1400 mL/min. The H2O2/UV-C process achieved a TOC removal rate of 369 mgC/h and over 98% color removal after 4 h of treatment, when a single dose of 6 g/L H2O2 and 11.8 W/L of UVC irradiation dose were applied. Finally, the combined process (AO/H2O2/UV-C) led to a faster TOC abatement (534 mgC/h) and a higher color removal, after treating the wastewater with 77 mA/cm2 current density, 5.9 W/L UVC irradiation dose and ‘on-line’ dosing 15.7 g/L H2O2.