Tannery wastewater treatment by electro-Fenton and electro-persulfate processes using graphite from used batteries as free-cost electrode materials

Treatment of wastewater originated from tannery in Cameroon by electro-Fenton (EF) and electro-persulfate (EP) processes using graphite as free-cost electrodes was investigated in this study. Graphite obtained from recycled spent lithium ion batteries and used as anode and cathode in an electrochemical device for degradation studies. Degradation study was evaluated based on the COD removal. Effect of current density, electrolysis time and the concentration of the electrolyte investigated, to evaluate the most suitable process and least energy consumption. Using the electro-Fenton process, the treatment reached a maximum reduction of 67.25% for COD removal under the following conditions: pH (3), I = 300mA, [Fe 2+ ] = 0.1 mM, time = 6 h, meanwhile electro-persulfate process led to the removal of COD up to 95.62% under the following conditions: pH = 3, I = 300mA, [S 2 O 8 2− ] = 0.6mM and time 6 h. The energy consumption for high removal of COD showed that EF and EP have a cost of 8.357 and 6.867 kwh/gCOD respectively. EP was found to be the most efficient method for the degradation of tannery wastewater, since this technic has the lowest cost of operation. Thus, EP proved to be an appropriate technique for the removal of organic load from tannery wastewater. • First report of electro-persulfate process in the treatment of tannery wastewater. • Valorization of graphite material as free-cost electrode in the degradation of tannery wastewater. • Electro-persulfate led to high COD removal (95.62%) after 6 h of electrolysis. • Total cost of EF process (8.357 kwh/gCOD) was found to be higher than that of EP process (6.867 kwh/gCOD).