Enhanced co-removal of nutrients and glyphosate from rural sewage in siphon-driven constructed wetlands: Optimization...

Constructed wetlands (CWs) often suffer from limited carbon/oxygen availability and poorly controlled redox conditions, constraining pollutant removal from rural sewage. Hence, siphon-driven CWs (S-CWs) were optimized for the co-removal of the typical rural pollutant glyphosate (N-(phosphonomethyl)glycine, PMG) and typical wastewater pollutants (carbon (C), nitrogen (N), phosphorus (P)). S-CWs exhibited strong PMG resilience, tolerating up to 8 mg/L, and achieved 50.91-92.14%, 50.93-56.82% and 96.19-97.18% for PMG, N and P removal, respectively. These results indicated superior performance compared with unaerated and aerated CWs. Mechanistic analysis showed that PMG removal was dominated by biodegradation in the aerobic, carbon-enriched inlet area of S-CWs. This process was driven by genera such as Alcaligenes and Geobacillus, and enzymes like PhnI, PhnJ via aminomethylphosphonic acid (AMPA) and C-P lyase pathways, as confirmed by metagenomics and AlphaFold 3 predictions. PMG transiently inhibited N removal by suppressing denitrification but not nitrification. However, microbial adaptation over 135 days restored N removal along the first 50% pathway, even under high PMG stress (10 mg/L). In contrast, P removal was more persistently inhibited throughout the system, as the additional PMG-derived P increased total P load and accelerated substrate adsorption saturation. Long-term operation confirmed the robustness of S-CWs, including reduced effluent toxicity, healthier plant growth, lower oxidative stress, and minimal clogging (only 1.40-13.53% porosity decline). These observations highlight the hydraulic stability and long-term suitability of S-CWs for treating PMG-laden rural wastewater.