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 degrees C, 10.66 <= i <= 25 mA cm(-2), [MB](0) = 134 mg L-1, and omega = 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).