Multifunctional Assessment of Natural and Waste-Derived Reactive Filter Media for Pollutant Removal and Temporal Aqueous Inorganic Carbon Responses in Constructed Wetlands

Constructed wetlands depend strongly on filter-media characteristics to achieve effective pollutant removal and support associated geochemical functions. This study evaluated basalt, dolomite, steel slag, and recycled aggregate for nutrient removal, heavy metal attenuation, and aqueous total inorganic carbon (TIC) responses. Treatment performance was evaluated descriptively using observed pollutant-removal efficiencies and temporal changes in aqueous TIC concentrations. Steel slag exhibited the highest observed total nitrogen (TN) (32.3%) and total phosphorus (TP) (62.0%) removal efficiencies at 120 min. It also showed the highest observed Zn (97.1%) and Cu (66.4%) removal efficiencies among the tested media. Recycled aggregate exhibited a 90.0% increase in effluent TIC concentration between the first and fifth monitoring weeks, while steel slag showed a 63.5% increase. In contrast, basalt and dolomite exhibited decreases of 31.9% and 68.7%, respectively. Principal component analysis (PCA) characterized differences in pollutant-removal profiles among the four media, with the first two principal components explaining 70.9% of the total variance. The integrated descriptive assessment showed that steel slag had the highest numerical average overall pollutant-removal efficiency (62.3%) under the tested conditions, together with a positive temporal aqueous TIC response. These findings suggest that reactive and waste-derived filter media warrant further investigation for multifunctional constructed-wetland applications. However, observed changes in aqueous TIC may reflect mineral–water interactions and atmospheric CO2 exchange and should not be interpreted as direct evidence of carbonate mineralization or permanent carbon sequestration.