Electrochemical Pre-Treatment Combined with Biological Treatment for the Degradation of Methylene Blue Dye: Pb/PbO2 Electrode and Modeling-Optimization through Central Composite Design

Electrochemical pretreatment of wastewater containing methylene blue was studied on an Pb/PbO2 electrode and showed enhancement of the color removal efficiency for increasing current density and decreasing dye concentration. The effect of the temperature was more pronounced at a high initial dye concentration (134 mg L–1) compared to a low initial concentration (12 mg L–1), whereas it was the opposite for the agitation speed. The model obtained by central composite design led to the following optimal conditions for MB degradation: 41 ≤ T ≤ 60 °C, 10.66 ≤ i ≤ 25 mA cm–2, MB0 = 134 mg L–1, and ω = 720 rpm, which gave 95.61% degradation efficiency. Electrolysis improved biodegradability from 0.034 to 0.54 for the BOD5/COD ratio, indicating the feasibility of a biological treatment combined to an electrochemical pretreatment process. The degradation of the generated intermediate compounds was performed using activated sludge and led to 92.03% mineralization (overall DOC removal).