Tracing the electron transfer behavior driven by hydrophyte-derived carbon materials empowered autotrophic denitrification in iron-based constructed wetlands: Efficacy and enhancement mechanism

Yuanyuan Fan; Shanshan Sun; Xushun Gu; Pan Yan; Yu Zhang; Yuanjun Peng; Shengbing He

doi:10.1016/j.watres.2025.123169

Tracing the electron transfer behavior driven by hydrophyte-derived carbon materials empowered autotrophic denitrification in iron-based constructed wetlands: Efficacy and enhancement mechanism

Water Res. 2025 Jan 21:275:123169. doi: 10.1016/j.watres.2025.123169. Online ahead of print.

Authors

Yuanyuan Fan¹, Shanshan Sun², Xushun Gu¹, Pan Yan¹, Yu Zhang¹, Yuanjun Peng¹, Shengbing He³

Affiliations

¹ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China.
² School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China; Shanghai Jiao Tong University Yunnan Dali Research Institute, PR China.
³ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China. Electronic address: shengbing_he@163.com.

PMID: 39855019
DOI: 10.1016/j.watres.2025.123169

Abstract

Iron-based constructed wetlands (ICWs) displayed great potential in deep nitrogen elimination for low-polluted wastewater. However, the unsatisfactory denitrification performance caused by the limited solubility and sluggish activity of iron substrates needs to be improved in an eco-effective manner. To fill this gap, the bioavailability of iron substrates (iron scraps) affected by wetland biomass-derived carbon materials with potential conductivity were explored. Results indicated that the cumulative removal of TN in biochar-added ICW (BC-ICW) and activated carbon-added ICW (AC-ICW) increased by 29.04 % and 22.96 %, respectively. The carbon matrix of AC played the geo-conductor role to facilitate the rapid release of iron ions, as indicated by the higher TN removal efficiency of AC-ICW (45.36 ± 1.45 %) at the early stage, while the reduced conductivity of AC negatively impacted the nitrogen removal. BC-ICW exhibited intensified denitrification potential, with higher TN removal capacity (52.08 ± 3.04 %) and effluent Fe²⁺ concentration. Electroactive bacteria (EB) (Geobacter, Desulfovibrio, Shewanella, etc.) associated with extracellular electron transfer were enriched in BC-ICW, as well as the expanded niches breadth and improved microbial community diversity. The electron-shuttling effect of BC was mainly attributed to its oxygenated functional groups (quinone/phenolic moieties), which supported the electron transfer from EB to extracellular iron oxides, as evidenced by the increased Fe(III)(hydro)oxides bioavailability. Besides, biochar concurrently up-regulated the gene expression of electron transport chains/mediators and denitrification reductases, suggesting that BC boosted the active iron cycle and iron-mediated autotrophic denitrification in ICWs by accelerating intracellular and extracellular electron transfer. This work explored the electron transfer behavior of biomass-derived carbon materials coupled with ICWs to enhance denitrification, providing insights into the sustainable application of biomass derived carbon-assisted ICWs in tertiary treatment.

Keywords: Activated carbon; Autotrophic denitrification; Biochar; Coupling mechanism; Electron transfer behavior; Iron-based constructed wetlands.