Regeneration of Rhodamine B saturated activated carbon by an electro-peroxone process

Abstract

Due to the lack of feasible regeneration methods, spent powdered activated carbon (PAC) is conventionally disposed of by incineration or landfill after its adsorption capacity is exhausted in adsorption applications. In this study, an electro-peroxone (EP) process (a combined process of conventional ozonation and in situ cathodic hydrogen peroxide (H2O2) production) was proposed to regenerate PAC saturated with Rhodamine B (RhB) dye. Results show that the adsorption of RhB onto PAC involved primarily irreversible chemisorption. Therefore, the RhB-saturated PAC could not be regenerated upon dilution by water washing. In contrast, by oxidatively converting irreversibly sorbed RhB to more desorbable oxidation by-products (e.g., carboxylic acids), both ozonation and the EP regenerations could restore >90% of the adsorption capacity of the PAC for RhB reloading. However, ozonation regeneration could not effectively mineralize the desorbed pollutants due to the selective oxidation characteristics of ozone (O3). In contrast, due to the substantial generation of hydroxyl radicals (OH) from the reaction of bubbled O3 with electro-produced H2O2, the EP regeneration was capable of completely mineralizing the desorbed pollutants. During the EP regeneration, PAC was oxidized to some extents, thus gradually losing its adsorption capacity. By optimizing the applied current, ozone dose, and regeneration time, ∼76% of the adsorption capacity of the virgin PAC could still be retained after five cycles of RhB adsorption and the EP regeneration. The results of this study indicate that the EP process may provide an environmentally-friendly and sustainable way to regenerate spent PAC for reuse.