Spontaneous Oxidation of Organic Matter and Ammonium Uptake from Manure Wastewater by Redox-Active Materials

Spontaneous NH4+ uptake using solid-state redox-active materials, driven by the oxidation of organic matter in manure wastewater, provides a sustainable and energy-friendly method for nutrient recovery. However, the mechanisms of electron transfer and accompanying ion transport are poorly understood. Here, we investigated the electron transfer pathway and NH4+ uptake mechanism by analyzing the composition changes in manure wastewater via NMR and the corresponding electrochemical results. We found that the spontaneous NH4+ uptake involves a direct electron transfer process without redox mediators, with the co-occurrence of ion intercalation and adsorption. Based on the elucidated mechanisms, a core–shell Prussian blue analogue redox material with improved stability in manure wastewater and enhanced NH4+ recovery compared to previously reported electrode materials was developed. Such a fundamental understanding of the oxidation of organic compounds and spontaneous NH4+ uptake by redox-active materials can guide the design of redox materials for effective resource recovery and environmental applications.