Electrochemical Methods for Ammonia Separation from Wastewater

The mass production of ammonia fertilizer via the Haber-Bosch process has enhanced agricultural productivity and supported the global population growth, but ammonia discharge from wastewater into natural waters causes eutrophication, harming aquatic ecosystems. Moreover, both ammonia synthesis and removal are highly energy-intensive processes, with Haber-Bosch process consuming approximately 2% of the world’s primary energy. Electrochemical ammonia recovery (ECAmR) has emerged as a promising solution, offering a chemical-free operation with greater energy efficiency compared to conventional methods. This review provides a comprehensive overview of the ECAmR strategies based on their mechanism on ammonia selectivity: (1) pH-shift mediated system water electrolysis (WE), bipolar membrane electrodialysis (BMED), and (2) electrosorption-mediated system (capacitive deionization (CDI), intercalation). The superior performance of these systems was validated with low energy consumption and a high removal rate exceeding 70%, while operations were concentration dependent. Furthermore, we comprehensively examined the contrasting features of each system to evaluate practical challenges for real wastewater applications. For the commercialization of ECAmR, ensuring long-term operation through electrode stability is essential, which requires enhancing structural stability and mitigating side reactions. Furthermore, we provided guidance on future techno-economic analysis (TEA) and life cycle assessment (LCA) frameworks for ECAmR systems to substantiate the practical viability of technology. Ultimately, this research aims to clearly diagnose the current status of ECAmR and provide a future research direction to establish a sustainable nitrogen cycle system.