High-rate ammonium removal and recovery and hydrogen production from wastewater using microbial electrolysis cell

This study presents an integrated approach combining microbial electrolysis cells (MECs) with three external ammonium extraction systems, Gas Diffuser (GD), Stripping Column (SP) and Thermally Assisted Stripping (SP + T), to enhance nitrogen removal and recovery from high-strength wastewater. Among the configurations, MECs operated at 0.75 V and integrated with SP + T achieved the highest performances, with current density of 8.8 A m^-2, ammonium removal and recovery rates reaching 69.8 and 37.9 gN m^-2 d^-1, Faradaic efficiency of 74.9 % and specific energy consumption for ammonium recovery of 3.3 kWh kg^-1N. The SP + T system boosted ammonia volatilization at the catholyte and accelerated ammonium transport across the cation exchange membrane, leading to improved removal and recovery performance. Concurrently, H₂ generation reached 1557.6 L H₂ m^-3 d^-1 with specific energy consumption of 31.4 kWh kg^-1 H₂. These results highlight that coupling MEC and SP + T is a promising configuration for efficient nitrogen recovery and renewable hydrogen generation, while demonstrating MECs as a sustainable technology for wastewater treatment and resource recovery. STRUCTURED ABSTRACT: The study presents a novel approach for enhancing nitrogen recovery from wastewater using MECs integrated with different ammonium stripping systems. By evaluating three configurations, gas diffuser (GD), ambient-temperature stripping (SP) and thermally assisted MEC stripping system (SP + T), this work systematically investigates how operational strategies affect the performance of nitrogen removal and recovery. Key performance indicators such as current density, Faradaic efficiency, specific energy consumption and hydrogen production are quantified and compared as well. Furthermore, organic removal rates, percentage and energy efficiency of organic matter treatment in the anode are also assessed. The findings described highlight the importance of optimizing operational parameters such as temperature and contact surface to maximize ammonium recovery in MECs. The SP + T approach is relevant for bioelectrochemical and wastewater treatment systems aiming to optimize nitrogen management and valorization. Furthermore, the study includes a comprehensive energy analysis and contextualizes the results with respect to conventional ammonia production technologies such as the Haber-Bosch process, among others. Thus, these results are of relevance to the fields of wastewater treatment, nutrient recovery, energy/hydrogen production, environmental biotechnology and circular economy, offering a scalable and energy-efficient solution for nutrient valorization.