Optimizing calculation method for zeolite unit thickness of a permeable reactive barrier coupling adsorption with simultaneous nitrification-denitrification for landfill leachate polluted groundwater

Ammonium-nitrogen (NH₄ ⁺-N) can be efficiently removed by permeable reactive barrier (PRB) technology for landfill leachate polluted groundwater. The thickness of zeolite unit plays a critical role in defining the operational longevity of zeolite-based PRB. It is vital to calculate the zeolite unit thickness and predict changes in its saturated state. Nonetheless, few studies have conducted to ascertain the zeolite unit thickness by combining the biological nitrification rate constant with the equilibrium adsorption capacity of zeolite. To treat NH₄ ⁺ -N-contaminated groundwater and predict the change of zeolite unit, sequential column experiments were performed. Besides, an optimized calculation method for the zeolite unit thickness was provided in this study. Nano-aeration for oxygenation and the addition of external carbon sources were adopted in Aerobic Column and Denitrification Column, respectively. The results of column experiment indicated that the removal rate of NH₄ ⁺ -N and total nitrogen could reach 99 % during the 123 pore volumes (PVs) operation cycle. Moreover, denitrification occurred in Aerobic Column due to the localized low oxygen environment and the enhanced ratio of COD to total nitrogen. The first-order rate constants of zeolite adsorption, nitrification and denitrification in Aerobic Column were 0.5213–0.7693, 0.0384–0.0858 and 0.1376–0.2233 h^-1, respectively. Moreover, the calculation of zeolite unit thickness was optimized based on the nitrogen mass balance between influent and effluent, which combined the biological nitrification rate constant and the equilibrium adsorption capacity of zeolite. This optimized method for calculating zeolite unit thickness not only predicts saturated zeolite unit thickness over operating time, but also reduces the cost of PRB.