Nitrogen pollution diagnosis and targeted nitrate removal in a historic urban moat using a novel Fe-Mn oxide composite

Building upon a diagnostic assessment of nitrogen and phosphorus pollution in the Jingzhou Moat, this work developed a novel Fe-Mn oxide composite for the targeted removal of nitrate. An assessment of the water quality revealed a typical pattern of low phosphorus and high nitrogen pollution, with nitrate being the predominant contaminant. A novel Fe-Mn oxide modified activated carbon (FeMnAC) composite with a well-anchored MnFe 2 O 4 spinel structure was synthesized using a controlled activation, impregnation, and calcination procedure. The composite has an increased point of zero charge (pH 9.6), allowing for excellent nitrate adsorption throughout a wide pH range (2∼10). The adsorption process follows the Langmuir monolayer chemisorption model, with a maximum adsorption capacity of 23.19 mg·g −1 . FeMnAC demonstrated exceptional selectivity in the presence of competing anions like PO 4 3– while achieving highly efficient nitrate removal in real moat water samples in 120 min. After four regeneration cycles using NaCl, the adsorbent showed good reusability, retaining more than 50% of its initial capacity. This work offers a transferable methodological framework for nitrogen pollution control in similar heritage urban water systems by combining pollution diagnosis, targeted material design, and practical validation.