Trade-off between electrochemical and microbial nutrient eliminations in iron anode-assisted constructed wetlands:...

Holistic understanding of electrocatalytic behaviors and microbiological mechanisms respond to voltage level (VL) benefits constructing performance-pathway-community linkages in iron anode-assisted constructed wetlands (IACWs). Herein, five solar-driven IACWs at 0, 1, 5, 10, and 15 V were established to treat secondary effluent for 109 days across moderate to low water temperatures (WTs). Results showed that total nitrogen (TN) (4.87-54.42%) and total phosphorus (TP) (20.66-97.35%) removals both ascended as VL raised, which primarily occurred in the cathodic regions and anodic upstream, respectively. More sustainable nitrogen elimination was achieved at lower VLs (≤ 5 V). Electrochemical contribution quantification revealed that electrochemical denitrogenation strengthened as VL improved (144.3-965.7 mg m^-2 d^-1), whereas severe anodic hardening and cathodic clogging in later operation impaired the dominant electrochemical denitrification at higher VLs (≥ 10 V). In contrast, microbial denitrogenation followed hump-shaped variational pattern with rising VL (peaked at 5 V). Microbial community and function analyses further clarified that despite VL elevation induced denitrifying microbiota evolution and up-regulated functional gene abundance, microbial denitrification function was significantly constrained at higher VLs. Particularly, the highest network complexity (at 1 V) and modularity (at 5 V) bred IACWs to better withstand low WT and high iron concentration. Overall, 5 V balanced electrochemical and microbial denitrogenation to obtain persistently effective TN removal. Additionally, intensified electro-coagulation dephosphorization was verified to remove most TP via adsorption and co-precipitation. This work provided a preferred VL regulation strategy to facilitate in situ sustainable nutrient purification of low-polluted wastewater in IACWs.