Performance of an Fe/Mn-modified substrate–micro-aeration bioelectrochemical constructed wetland for treating real food industry wastewater

Traditional constructed wetlands (CWs) generally lack effective regulation of redox conditions and electron-transfer processes, which limits the stable conversion of NH 4 + –N and further removal of total nitrogen (TN). In this study, a bioelectrochemical constructed wetland (BES-CW) integrating electrode enhancement, Fe/Mn-modified substrates, and intermittent micro-aeration was constructed to treat real industrial wastewater from a food industrial park and was evaluated in terms of treatment performance, potential nitrogen-transformation processes, and engineering applicability. During the intermittent micro-aeration stage with an applied voltage of 4 V and an air-to-water ratio of 0.5:1, the BES-CW achieved removal efficiencies of 83.88%, 81.12%, 82.26%, and 88.91% for NH 4 + –N, TN, chemical oxygen demand (COD), and total phosphorus (TP), respectively, showing overall higher treatment performance than the two simultaneously operated control configurations. X-ray photoelectron spectroscopy (XPS) results showed that Fe 2+ /Fe 3+ and Mn 2+ /Mn 3+ /Mn 4+ remained in coexisting multivalent states after operation, indicating the potential of Fe/Mn components to participate in redox transformations and electron transfer. Microbial community composition and functional gene profiles further indicated functional potentials associated with denitrification, heterotrophic nitrogen transformation, and Fe/Mn-related electron transfer, providing indirect evidence for multiple potential nitrogen-transformation pathways. The engineering economic analysis showed that, under the same nitrogen-removal target, the major construction cost of the BES-CW was approximately 17.8% lower than that of a conventional CW, while the operating cost was 0.167 USD/m 3 , indicating promising engineering applicability of the BES-CW.