Experimental and Theoretical Study of Ammonium Nitrogen Adsorption on Natural Zeolite Using Synthetic and Real Reverse Osmosis Pretreated Landfill Leachate

Natural zeolite was investigated for ammonium nitrogen (NH4+–N) removal from both synthetic aqueous solutions and real pretreated landfill leachate using batch and continuous-flow systems. Batch experiments were conducted at initial NH4+–N concentrations ranging between 5 and 35 mg/L and zeolite dosages ranging between 10 and 50 g/L. Additionally, real pretreated landfill leachate (35 mg/L NH4+–N) was treated using zeolite dosages of 10–75 g/L, achieving removal efficiencies up to 94%. Equilibrium and kinetic data were analyzed using Langmuir and Freundlich isotherms and pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. The Freundlich isotherm and PSO model best described the experimental data, indicating heterogeneous, multilayer adsorption governed primarily by chemisorption mechanisms. Continuous fixed-bed column experiments were performed under various flow rates, initial NH4+–N concentrations, and zeolite masses. The resulting breakthrough curves were modeled using the Clark and modified Clark models, with the modified form showing improved predictive performance. The experimental data were further utilized to develop a MATLAB-based global fitting algorithm incorporating shared parameters across operating conditions. The model demonstrated strong predictive capability for fixed-bed breakthrough behavior. Overall, the results highlight the effectiveness of natural zeolite applicability as a low-cost and efficient post-treatment adsorbent for ammonium removal from complex wastewater streams.