Electrosorption of phenolic compounds from olive mill wastewater: Mass transport consideration under a transient regime through an alginate-activated carbon fixed-bed electrode.

Olive mill wastewater (OMWW) is an environmentally critical effluent, specifically due to its high content of phenolic compounds (PCs), which are hazardous due to their antimicrobial activities in water. However, their properties have good health effects at suitable doses. For the first time, the electrosorption of PCs from actual OMWW has been proposed for their possible recovery as value-added compounds, while decontaminating OMWW. A bio-sourced alginate-activated carbon (AC) fixed-bed electrode was prepared based on the reuse of olive pomace solid waste as powdered AC. At the optimal AC content (1% w/v), the internal ohmic drop voltage was lower (2.26 V) and the mass transport coefficient was higher (9.7 10−5 m s−1) along with the diffusivity (7.3 10−9 m2 s−1), which led to enhanced electrosorption rates. Afterward, an optimal electrode potential was obtained (−1.1 V vs. Ag/AgCl), while higher voltages led to faradaic reactions. Moreover, the adsorption capacity was lower (123 mg g−1) than that of electrosorption (170 mg g−1) and was even higher (307 mg g−1) with actual effluents. This was probably due to the influence of electromigration, which was confirmed by new models that could predict the electrosorption kinetics well considering mass transport and acid dissociation constants. [Display omitted] • Electrosorption of phenolic compounds with real olive mill effluents for the first time. • New model of phenol electrosorption kinetics including transport in transient regime. • Electro-migration was added to diffusion in electrosorption model of real effluent. • Mass transport was correlated with the activated carbon content in alginate beads. • Electrosorption occurred mainly within the beads and not at the electrode interface. [ABSTRACT FROM AUTHOR]