The challenging removal of emerging pollutants: electrochemical regeneration to recover the adsorption capacity of a caffeine-saturated activated carbon

The treatment of emerging pollutants is challenging due to the very low concentration in which they are found in nature, along with their general recalcitrant characteristic. One way to overcome these limitations is combining a pre-concentration step followed by the degradation of the concentrated pollutant. This can be achieved in a first adsorption step, followed by a second electrochemical carbon regeneration/pollutant degradation. This study applies this principle to caffeine treatment by coupling adsorption on activated carbon (AC) with electrochemical regeneration/caffeine degradation onto a boron-doped diamond (BDD) anode. The AC is morphologically and structurally characterized by N-2 adsorption/desorption experiment (surface area) and scanning electron microscopy (surface morphology). The isoelectric point of the AC is measured to identify the surface charge depending on the pH, and the equilibrium isotherms allow us to estimate the caffeine adsorption capacity. The concept of adsorption/electrochemical regeneration is applied to caffeine treatment, analyzing the influence of operating parameters such as the fluidization of the carbon, the electrolyte, and the applied current. Under AC fluidization, using NaCl as the electrolyte and a current density of 0.5 A, a regeneration efficiency of 87% can be achieved. Furthermore, after 5 adsorption/regeneration cycles, this parameter slightly drops to 80%, demonstrating its capacity to preserve the carbon capacity and effectiveness in recovering the AC. Finally, the intermediates formed during the electrochemical regeneration are also identified.

Automated summary

The study combines activated carbon adsorption and electrochemical regeneration/caffeine degradation and applies it to caffeine treatment. The activated carbon is characterized and the caffeine adsorption capacity is estimated. The influence of operating parameters on caffeine treatment is also analyzed. Under the conditions of activated carbon fluidization, NaCl as the electrolyte, and a current density of 0.5 A, a regeneration efficiency of 87% can be achieved. Intermediates formed during the electrochemical regeneration are also identified.