Electro-sorption/-desorption with bio-sourced granular activated carbon electrode for phenols recovery and combination with advanced electro-oxidation for residual olive mill wastewater treatment

To face the releasing of hazardous solid and liquid wastes into the environment from the olive oil production industry, it is newly proposed a circular economy approach by implementing electro-sorption of value-added phenolic compounds (PCs) followed by electro-desorption using a bio-sourced granular activated carbon (GAC) electrode made of olive pomace waste. The remaining organic compounds present in the real olive mill wastewater (OMWW) were treated by advanced electrooxidation.

The PCs electro-sorption study highlighted efficiency around 72 % in synthetic matrix against 68 % in real effluents, whose electro-sorption capacities could be partly attributed to the high electroactive surface area (7.8 × 10³ cm²), high exchange current intensity (I₀) value (5.5 × 10⁻³ A), and low charge transfer resistance (R_CT) value (4 Ω) compared to the literature. The study further emphasized the fact that the electro-sorption selectivity was not only dependent on pKa of PCs with respect to solution pH, but also on the size of adsorbed molecules relative to the pore size distribution of GAC. The maximal percentage of PCs recovered from GAC after electro-desorption experiments was 34.5 %, while the global chemical oxygen demand (COD) removal efficiency was 92 % of the pre-filtered real effluent at the cost of scaling during advanced electrooxidation of residual OMWW.