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Enhanced nitrogen and phosphorus removal and microbial community response in constructed wetlands using iron-manganese bimetallic modified biochar as substrate for rural wastewater treatment
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DOI：10.3389/fenvs.2026.1879204.png)
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Abstract
En 中文
IntroductionConventional constructed wetlands (CWs) often exhibit limited efficacy in removing total nitrogen (TN) and total phosphorus (TP) from rural wastewater with low and fluctuating carbon‐to‐nitrogen (C/N) ratios. This study developed an iron‐manganese (Fe‐Mn) bimetallic modified rice husk biochar (Fe‐Mn‐BC) as an enhanced CW substrate.MethodsFe‐Mn‐BC was synthesized via FeCl3/MnCl2 co‐impregnation; alkali precipitation; and pyrolysis; and applied in four parallel vertical‐flow reactors (CW‐G; CW‐BC; CW‐Fe‐BC; CW‐FeMn‐BC) operated under three sequential C/N regimes (1; 3; 5). Material properties were characterized by XRD; SEM‐EDS; FTIR; and BET; microbial responses were assessed by 16S rRNA sequencing and qPCR.ResultsCharacterization confirmed coexistence of α‐FeOOH; Fe3O4; and δ‐MnO2 phases with Fe and Mn loading of 73.4 and 69.8 mg g‐1. Under the most stringent C/N = 1 condition; CW‐FeMn‐BC achieved TN and TP removal of 62.4% and 92.7%; with a low TN response slope of 4.55% per C/N unit (approximately 55% of CW‐BC). Sequencing and qPCR revealed selective enrichment of ammonia‐oxidizing; iron-oxidizing; and iron‐reducing bacteria; accompanied by marked upregulation of nirS (12.5‐fold); hzsA (21‐fold); cyc2 (15.8‐fold); and phoD (4.2‐fold) functional genes.DiscussionThese findings demonstrate that Fe‐Mn‐BC enables a material‐chemical‐biological tri‐synergy for enhanced N and P removal; offering a sustainable substrate strategy for decentralized rural wastewater treatment under fluctuating low C/N conditions.
Keywords:
constructed wetland
functional gene upregulation
iron-manganese bimetallic biochar
low C/N rural wastewater
microbial community response
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