Removal of ammonium from wastewater by zeolite synthetized from volcanic ash: Batch and column tests

Volcanic ash (VA) fallout during explosive activity of Mt. Etna (Sicily, Italy) negatively impacts the economy of local municipalities due to the management and disposal costs. In order to investigate an alternative use of VA in the civil and environmental engineering field, zeolites synthetized from VA were employed to remove ammonium from various aqueous solutions. Specifically, batch adsorption experiments were conducted to assess the effect of different synthesis conditions (e.g., incubation temperature, use of seawater or distilled water, VA particle size) on the adsorption capacity of ammonium on the produced zeolites. Adsorption isotherms were well fitted by Freundlich model and showed that zeolite synthetized at 70 °C using distilled water (C1H70) exhibited the highest adsorption capacity (~18.4 mg g−1). The observed ammonium adsorption capacity is higher or comparable to other natural or synthetized zeolites reported in literature. C1H70 was used in column experiments under different operational conditions, including initial ammonium concentration (10 and 40 mg L−1), empty bed contact time (EBCT, 4 and 8 min) and water quality (deionized water vs. secondary effluent wastewater). The Dose-Response model showed the best fitting in describing the breakthrough curves. Obtained results showed a good removal of ammonium even though the adsorption capacity decreased in presence of competing ions (e.g., calcium) and when tap water or wastewater was used. Moreover, the adsorption capacity of C1H70 regenerated through NaCl solution was found similar to the fresh C1H70. However, the regenerated zeolite was characterized by a slower mass transfer process. Overall, synthetized zeolites from VA can be used to remove ammonium from wastewater, reducing both the landfilling of VA and the extraction of natural zeolite under the circular economy perspective.