A Process Model for Leachate Treatment in Adsorbent-Amended Constructed Wetlands

This paper introduces a model of constructed wetlands (CWs) for on-site landfill leachate treatment, emphasizing the efficacy of zeolite and biochar as adsorbent media to enhance pollutant removal. While zeolite improves nitrification, biochar enhances denitrification and organic matter removal. The model employed a series of continuously stirred reactors and was calibrated and validated using data from 2 parallel CW mesocosms. Each mesocosm incorporated a 250-L vertical subsurface flow CW (V-CW) followed by a 440-L horizontal subsurface flow CW (H-CW). One was an unamended control with gravel media and the other was amended with zeolite in V-CW and biochar in H-CW. The model considered hourly changes in water storage, temperature, and transformations of nitrogen species, chemical oxygen demand (COD), and dissolved oxygen. Model robustness was demonstrated by low normalized root mean square error values (<0.3) for effluent ammonium nitrogen and COD concentrations. The model, validated and subject to a sensitivity analysis, accurately predicted pollutant removal efficiency (<13.3% error for unamended, <3% for adsorbent-amended), making it a valuable tool for evaluating full-scale CW dynamic performance under variable conditions.