Adsorption and desorption of ammonium from treated wastewater by zeolite filled columns: An experimental study at the water resource recovery facility of Palermo University – Italy

Water scarcity and mineral fertilizer depletion are becoming recognised environmental challenges worldwide. Treated wastewater (TWW) could be a potential resource for reusing water and nutrients, such as nitrogen (N), for fertilizers. This study explores the possibility of adopting columns filled with zeolite to recover ammonium (NH₄⁺) from real TWW. Specifically, this study aimed to evaluate zeolite's adsorption capacity with different particle sizes arranged in columns and various flow rates to determine the most efficient way of NH₄⁺ adsorption from a real wastewater treatment plant's effluent. The same zeolite with two different size diameters (0.5-1.0 mm and 2.0-5.0 mm) was tested using three different flow rates (1.2, 1.6 and 2.4 L h^-1) to evaluate their NH₄⁺ adsorption capacity. After the adsorption test, a desorption trial assessed the zeolite's desorption ability. The results showed that the highest flow rate increased the adsorption capacity of both zeolites by about 29% more than the lowest flow rate. Moreover, the 0.5-1.0 mm zeolite adsorbed approximately 60 mg more NH₄⁺ than the 2.0-5.0 mm zeolite, highlighting the influence of particle size on adsorption capacity. Furthermore, the zeolite was characterised by a rapid NH₄⁺ release since 44-78% of the adsorbed NH₄⁺ was released in the first 30 min. The desorption test with the lowest flow rate achieved the highest amount of desorbed NH₄⁺, up to 123-148% more than the higher flow rates. Results have shown that due to its adsorption capacity, zeolite can be used to recover NH₄⁺ from treated wastewater (TWW) and potentially recycle resources in the agriculture field, contributing to the circular economy.