Mass-Transfer Measurements by the Limiting-Current Technique

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.

Usability of alloys with different composition as electrode for electrochemical reduction of ferricyanide ion

An experimental work was performed to investigate the usability of 8 metallic alloys with different composition in electrochemical limiting diffusion current technique employing the cathodic reduction of ferricyanide. All the alloys exhibited a limiting current plateau region in their voltage–current behaviour, but not all gave a wide and smooth plateau, except one with almost pure Ni. With the alloys of including more than 50% Ni, as Ni ratio of the metal increased, smoother and wider plateau was attained, and the electrode containing 99% Ni gave the smoothest plateau. The other alloys tested can only be used as electrode in the limiting diffusion current technique in low flow velocities in which the transfer of the active ion to the electrode surface is as slow as that the mass transfer controls the rate of system.

Influence of number of azo bonds and mass transport limitations towards the elimination capacity of continuous electrochemical process for the removal of textile industrial dyes

This study focusses on the electrochemical decomposition of synthetic azo dyes (RO16, RR120 and DR80) using stainless steel electrodes, which is efficient, cost effective and industrially driven process. The experiments were carried out in a continuous electrochemical reactor and the effects of influencing parameters (initial concentration of dye, electrolyte concentration, pH) governing the process efficiency was studied. The interaction between the influencing parameters was investigated using Response Surface Methodology (RSM) and the regression value obtained for the generated model was above 0.9 for all the three dyes. The elimination capacity of electrochemical reactor was studied for the continuous removal of azo dyes with different ranges of concentration (100-400 mg L^-1) and flow rate (0.1-0.5 L h^-1). The maximum elimination capacity was obtained at a flow rate of 0.5 L h^-1 for 300 mg L^-1 of initial concentration of dye for RO16 and RR120 whereas it was 0.5 L h^-1 for 400 mg L^-1 of DR80. Further, a general dimensionless current density relation has been established for stirred tank reactor and allowed characterizing the relationship between kinetics and mass transport contributing to the overall reaction rate. The results quantitatively confirmed that the rate of electrochemical decolorization increased with the increasing initial dye concentration and flow rate due to the mass transport limitation. As newly established, the decolorization is also directly linked to the number of azo bonds.