Reactive black 5 dyeing wastewater treatment by electrolysis-Ce (IV) electrochemical oxidation technology: Influencing factors, synergy and enhancement mechanisms

• Electrolysis-Ce(IV) demonstrated excellent RB5 degradation and removal performance. • There is an obvious synergistic and enhanced effect between direct electrochemical oxidation process and Ce(IV) alone. • Direct electrochemical oxidation (39.5%), Ce(IV) catalytic oxidation (50.5%) and OH (1.6%) contributed much on RB5 removal in electrolysis-Ce(IV). • The background ions of HCO 3 − , PO 4 3− and HA have inhibitory effects, while Cl − has a promoting effect for RB5 removal. • Electrolysis-Ce(IV) has reasonable energy consumption. The intermediate products produced have good biochemical properties and low biological toxicity. Reactive black 5 (RB5) dyeing wastewater poses a serious threat to the water environment safety and biological life health. It is of great significance to use an enhanced type of electrolysis-Ce(IV) electrochemical oxidation technology for the efficient treatment of RB5 dyeing wastewater. In this study, the effects of single-factor experimental conditions such as cerium (Ce) ion concentration, pH, current value, different catalytic systems on RB5 degradation effect in electrolysis-Ce(IV) system were investigated. The experimental results showed a significant synergistic and enhanced effect between the direct electrochemical oxidation process and Ce(IV) treatment alone, and their combination (electrolysis-Ce(IV)) could significantly enhance the RB5 treatment with a removal efficiency up to 91.6%. In addition, the background ions HCO 3 − , Cl − , PO 4 3− and HA had an inhibitory effect on the electrolysis-Ce(IV) system, whereas Cl − had an enhanced effect. Meanwhile, reasonable energy consumption for the removal of RB5 was achieved in electrolysis-Ce(IV) with a maximum electrical energy per order (EE/O) value of 4.89 kWh·m −3 . There are three possible reaction ways for RB5 degradation, and the generated organic intermediates with low molecular weight and biotoxicity, which facilitates further mineralization of the product and biodegradation. In the electrolysis-Ce(IV) system, the driving force for the oxidative removal of RB5 were direct electrochemical oxidation function, Ce(IV) ions and hydroxyl radicals, where direct electrochemical oxidation function and Ce(IV) ions were the key and dominant effect for RB5 removal. Compared with the direct electrochemical oxidation system alone, the Ce(IV) in the electrolysis-Ce(IV) system contributes much to enhancing and improving the RB5 degradation and is the key and core active degradation substance.