Abstract

In this study, the performance of the anodic oxidation (AO) process was first evaluated for treating brewery wastewater using BDD/Graphite as electrodes, then Fe2+ was introduced into the system externally to investigate the combined effect of electro-Fenton (EF) and AO. The AO system showed up to 96% of COD removal with increasing current density yet a current density of 16 mA/cm2 was used for the rest of the analysis as increasing this parameter past this point improved the performance by only 5% yet consumed 51% more electrical energy. The EF-AO system showed a minor improvement in performance which prompted a hypothesis: the threshold catalytic amount of Fe2+ is already present in the brewery sample to initiate the Fenton reaction. Further analysis was performed to support this hypothesis: reactive oxygen species (ROS) and total Fe along with Fe2+ and Fe3+ speciation. The ROS (i.e. H2O2 and •OH) generation showed slight variations in AO and combined EF-AO process and iron speciation study showed significant reduction of Fe2+ over the electrolysis period and the available form of iron is Fe3+ which passivates easily at the experimental condition used, therefore, external addition of Fe2+ showed no improvement in performance. However, the pre-existing concentration of iron (66 µg/L) in brewery wastewater makes the treatment of this type of wastewater using anodic oxidation a dual performing system and therefore, shows satisfactory results. For this dual system, a set of experiments was performed to investigate the removal of COD, TN, and TP at different pH conditions with electrolytes. From these analyses, the removal efficiencies were found to be 94, 86, and 100% for COD, TN, and TP respectively at a pH of 7.