A kinetic-based zeolite PRB design method for remediating groundwater polluted by high NH₄⁺ MSW leachate considering spatio-temporal concentration evolutions

Albeit the widely-used zeolite permeable reactive barriers (PRBs) in remediating ammonium in groundwater from mining industry and municipal solid waste landfills, the engineering design is primarily based on the traditional maximum adsorption capacity method and the residence time method. Both methods could predict neither the NH₄⁺ saturation versus time evolution, nor the breakthrough behavior of a zeolite PRB. This adds uncertainty to the PRB performance, on top of the conventional clogging and preferential flow problems. In this study, a kinetic-based method was proposed to tackle above challenges. An adsorption kinetic model was obtained based on two-variables batch test results, whereas the rate constant k was 0.1728 L/(min ⋅ mol), and the adsorption exponents with respect to both NH₄⁺ concentration and the zeolite adsorption site molarity were unity. Effective diffusion coefficient D^∗ (1 × 10⁻⁹ m²/s) and mechanical dispersion (α_L=8×10⁻³ m) were calibrated by Cl⁻ tracer tests. Three column tests with inlet NH₄⁺ concentrations of 200, 1000 and 2000 mg/L were performed to obtain the breakthrough curves, which agreed well (R² > 0.93) with those simulated by the proposed method. Indeed, breakthrough curves considering kinetics were also more precise than those with instantaneous adsorption assumption (R²=0.712-0.863). The proposed method was used for calculating the required thickness of a PRB for a municipal solid waste landfill, which was more conservative than those calculated by traditional methods.