Ammonia recovery and valorization from wastewater via adsorption, regeneration, and refining technologies

Ammonia (NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup>) present in wastewater represents a significant pollutant, contributing to eutrophication, depletion of dissolved oxygen, and increased toxicity within aquatic ecosystems. Simultaneously, ammonia serves as a critical raw material needed for fertilizer production and various industrial processes, which has made it the second most-produced chemical worldwide. Given ammonia's dual role as a wastewater contaminant and a valuable industrial product, the advancement of effective removal and recovery methods has assumed considerable significance. Adsorption-based processes have consequently received attention for their high efficacy in selectively separating and recovering ammonia from wastewater, along with their operational feasibility and simplicity. This review provides a comprehensive assessment of ammonia recovery from wastewater utilizing adsorption-regeneration processes, and explores advanced techniques for refining recovered ammonia into value-added nitrogen compounds, such as ammonium fertilizers, urea, nitric acid, and hydrogen gas. Furthermore, the importance of policy strategy (e.g., source separation) in ammonia recovery was discussed, along with the need for further policy research. This study presents a technological overview of the recovery and valorization of wastewater-derived ammonia into a valuable resource, highlighting sustainable wastewater treatment and nitrogen recovery technologies.