Nitrogen Removal Performance of Tidal Flow Constructed Wetlands Based on α-Fe2O3/Volcanic Rock Mixed Substrate
To enhance the adsorption performance of volcanic rock for nitrogen in water, an α-Fe2O3/volcanic rock composite was successfully prepared via ferric citrate impregnation and calcination. Its adsorption characteristics for NH4+-N and NO3−-N and application in tidal flow constructed wetlands (TFCWs) were systematically investigated. Results showed that the adsorption kinetics of both nitrogen forms followed a pseudo-second-order model, indicating chemisorption dominance. Langmuir and Freundlich isotherm models both fitted the data, suggesting coexistence of monolayer and multilayer adsorption. The saturated adsorption capacities of α-Fe2O3/volcanic rock for NH4+-N and NO3−-N were 0.055 mg·g−1 and 0.067 mg·g−1, respectively. In TFCWs using this composite as substrate, average removal efficiencies for NH4+-N and NO3−-N reached 72.51% and 68.13%, respectively. Furthermore, microbial community abundance and diversity in the wetland system significantly increased, indicating that α-Fe2O3 introduction effectively enhanced microbial activity, thereby improving nitrogen removal efficiency.