Nitrogen Removal Performance of Tidal Flow Constructed Wetlands Based on α-Fe2O3/Volcanic Rock Mixed Substrate

• • α-Fe2O3/volcanic rock composite achieved saturated adsorption capacities of 0.055 mg·g−1 for NH4+-N and 0.067 mg·g−1 for NO3−-N, with kinetics fitting a pseudo-second-order model, confirming chemisorption as the dominant mechanism. • • In tidal flow constructed wetlands, the composite substrate yielded average removal efficiencies of 72.51% for NH4+-N and 68.13% for NO3−-N, outperforming conventional volcanic rock under identical operational conditions. • • Varying the submerged-to-drained ratio significantly impacted performance: NH4+-N removal was highest at 81.75% with a 1:2 ratio, while NO3−-N removal peaked at 83.82% with a 2:1 ratio, demonstrating opposite trends with inundation time. • • Microbial community analysis at a 1:2 ratio revealed highest abundance and diversity, with dominant phyla including Bacteroidota, Proteobacteria, and Chloroflexi, and key families such as PHOS-HE36, Anaerolineaceae, and Gemmatimonadaceae, indicating enhanced biological activity.